When you removed the chip did any of the plated through holes loose the plating? I think the board is up to six layers. You may have lost an internal connection to the chip.


Tom

----- Original Message -----
From: nielsentelecom@...
To: TekScopes@...
Sent: Tuesday, February 19, 2013 12:10 PM
Subject: [TekScopes] Re: 2246 Mod A - no trace



Priya,

Wow, I didn't know it was all channels! Check your trigger setting, try a single shot too. maybe your focus is so far out you can't see it. Look at it in the dark too. Check the rejection section in the trigger area, set it for DC. Use the menu to set things to default just in case you got into unfamiliar territory. I don't see how putting in that socket would have done anything else barring you accidently damaged something in the process or zapped something that is static sensitive.

Pull back for a second. Hopefully you just overlooked something!

Nick Nielsen

--- In TekScopes@..., "Mover" wrote:
>
> Hi Nick,
>
> There is currently no trace on any of the channels after installing the IC socket at U174. However, the beam finder works as do all the menus and also the vertical time base cursors and readouts. I suspect something with the motherboard now at or near U174. Using your plan, I will apply an identical calibration signal to Ch2 and Ch3 and compare what happens to the signal using my R7704 as a test scope. More to come on this ...
>
> Yes, I will be careful as you say to not blow up something else along the way!
>
> Priya.
>
> --- In TekScopes@..., "nielsentelecom@" wrote:
> >
> > Priya,
> >
> > You could probably use ch3 to probe for the comparisons as a last resort on the following.
> >
> > I would set up identical conditions on both ch2 and ch1. then on ch 2 compare signal traces starting at the input. Place the same signal on both leads(channels). Check the U175 relay driver on ch2 and find out if any are high. You can also check the U171/U172 if your input to the U174/U175 does not match. But they appear to do different jobs on given pins. Probably best to test at the inputs of U174 & U175. Then go forward till you lose identical signal. Since you don't have U174 installed, just the socket instead, U171 may be calling for one of the relays in the Ch1 circuit to be pulled in or activated if you prefer. Then jumper where U174 should be on the affected driver. If as you say the relays are all operating as they should, you should expect the ch1 and ch2 relays to all align identically. It is possible one of the relays just isn't pulled in correctly. You can also check test point 1A (AT117 pin 7) in the ch1 circuit, and At127 pin 7 to ensure the they match once you get both attenuators aligned the same.
> >
> > Don't forget, BE CAREFUL! Don't blow up ch2!!
> >
> > Nick Nielsen
> >
> >
> > --- In TekScopes@..., "Mover" wrote:
> > >
> > > Update: I soldered an IC socket in U174 thinking that I would connect leads to it externally to diagnose the Ch1 issue and now the trace has completely disappeared! The beam finder works, but when I release the beam finder button, there is nothing on the screen other than the vert and hor selection displays. The menus are all fine and the time cursors work fine too - just no signal trace. Checked all the voltages and they are fine.
> > >
> > > I assume that I have to use another scope to trace the vertical amplifier area, but would appreciate any tips here - if the vertical amplifier was bad, would it not also affect the beam finder, displays and menus?
> > >
> > > Priya Jakatdar.
> > >
> > > --- In TekScopes@..., "Mover" wrote:
> > > >
> > > > I put the scope back together and it runs fine on Ch2, Ch3 and Ch4 including time & frequency measurements. All secondary voltages are well within the spec range (7.48V, -7.47V, 5.2V, -5.2V, 15.1V, -15.9V etc), so I have not made any adjustment to the 44VDC rail to avoid calibrating the scope from scratch. Will use it this way for now and let it run for some time to be sure nothing else is wrong or will fail before attempting further repair.
> > > >
> > > > The issue with Ch1 and voltage measurements is a charred U174 transistor relay driver IC (Intersil 3082) that appears to have caused the SMPS to fail in the first place. I have not replaced the chip thinking there may be a larger issue with or around U174. The Ch1 individual relays are all working fine (tested with a Kikusui constant-voltage constant-current supply) and drawing 25 mA or 12 mA according to their spec. When I do get some time later, I am thinking about validating the Shift Register output pins of U171 that drives U174 first and then maybe installing an IC socket rather than soldering a new U174.
> > > >
> > > > I have searched the archives and not found anything specific with respect to U174. Any thoughts or previous experience with this will be greatly appreciated.
> > > >
> > > > I want to thank everyone's help in getting my scope back into working condition. I have learned a lot about my 2246 and it is mainly because of you guys.
> > > >
> > > > Priya.
> > > >
> > > > --- In TekScopes@..., "Mover" wrote:
> > > > >
> > > > > Tom,
> > > > >
> > > > > I was only able to get enough time to assemble the SMPS into the chassis with just the main board and it runs fine - without the 40W series bulb:). The voltages are a bit off (5.28V, 7.46V etc) but I won't adjust anything till the proc board and the pot boards are in and providing normal operating load.
> > > > >
> > > > > That's for the weekend. More to come.
> > > > >
> > > > > Thanks for taking the time to make resistance measurements - very similar to mine.
> > > > >
> > > > > Priya.
> > > > >
> > > > > --- In TekScopes@..., "Tom Jobe" wrote:
> > > > > >
> > > > > > Hi Priya,
> > > > > > Resistances were taken on a nice working 2246 with a Fluke 110 which does not have enough voltage to forward bias the diodes.
> > > > > > I tried this Fluke meter on some standard diodes and some Schottky diodes and there was not much of a connection either way, just a little leakage depending on the polarity
> > > > > > There is not much difference from your readings, and no obvious indication of a problem on any of the voltages.
> > > > > > I will add my readings on to the end of your list.
> > > > > >
> > > > > > > +5:100 ?? - mine is 99 ohm - 106 ohm
> > > > > > > -5:50 ?? - mine is 41 ohm - 53 ohm
> > > > > > > -15:500 ?? - mine is 750 ohm - 590 ohm
> > > > > > > +15:400 ?? - mine is 583 ohm - 483 ohm
> > > > > > > +7.5:150 ?? - mine is 134 ohm - 152 ohm
> > > > > > > -7.5:180 ?? - mine is 143 ohm - 150 ohm
> > > > > > > +58: 7500 ?? - mine is almost open ( 8M ohm) - 2.5 M ohm? impossible to get a good reading
> > > > > > > +130: 9000 ?? - mine is 10,000 - 9000 ohm
> > > > > >
> > > > > > I guess the next step is to see what happens when you put the scope back together tonight.
> > > > > > tom jobe...
> > > > > >
> > > > > >
> > > > > >
> > > > > > ----- Original Message -----
> > > > > > From: Mover
> > > > > > To: TekScopes@...
> > > > > > Sent: Friday, January 04, 2013 12:20 PM
> > > > > > Subject: [TekScopes] Re: 2246 Mod A main board overloading the SMPS
> > > > > >
> > > > > >
> > > > > >
> > > > > > Tom & Francis,
> > > > > >
> > > > > > I discovered what it is - the ultra cautious in me had left a 40W light bulb in series with the isolation transformer secondary providing AC line power to the scope. It was there originally to prevent further collateral damage to the scope through my repair and testing. With any load exceeding the load provided by the fan, the SMPS pulls enough current through the light bulb that the AC line power to the scope drops below the 80V required to keep the SMPS running. This shuts down the SMPS and the 40W bulb comes on as the SMPS restarts - absolutely normal behavior. I had completely forgotten about the light bulb till this afternoon when I chanced to glance at it cycling with the SMPS and then I had an AHA moment!
> > > > > >
> > > > > > Regardless, I did measure resistances (with a Fluke 116 - don't own a meter recommended by TEK) and here they are:
> > > > > > > +5:100 ?? - mine is 99 ohm
> > > > > > > -5:50 ?? - mine is 41 ohm
> > > > > > > -15:500 ?? - mine is 750 ohm
> > > > > > > +15:400 ?? - mine is 583 ohm
> > > > > > > +7.5:150 ?? - mine is 134 ohm
> > > > > > > -7.5:180 ?? - mine is 143 ohm
> > > > > > > +58: 7500 ?? - mine is almost open ( 8M ohm)
> > > > > > > +130: 9000 ?? - mine is 10,000
> > > > > >
> > > > > > Other than the 58V resistance probably becuase my meter can't drive the diodes, my measurements looks fine.
> > > > > >
> > > > > > I ran it without the series light bulb and it happily drives a 10 ohm resistor from the 5V and regulation is excellent at 5.05 VDC. With the light bulb in series, it won't run anything more than the fan. Indeed, the fan is not sufficient load to test the SMPS.
> > > > > >
> > > > > > Believe I am ready to put the SMPS back into the scope tonight. I apologize to everyone who I misled with my earlier post on this and thanks as always for quick and thoughtful responses. You guys are great!
> > > > > >
> > > > > > Priya.
> > > > > >
> > > > > > --- In TekScopes@..., "Francis" wrote:
> > > > > > >
> > > > > > > Hi,
> > > > > > >
> > > > > > > several things:
> > > > > > >
> > > > > > > as Tom Jobe suggested, you can do the following:
> > > > > > > with the scope disconnected from the mains, check the resistances
> > > > > > > between ground and each supply. As Tek says, use an ohmeter that is able to forward bias diodes, usually a low range.
> > > > > > >
> > > > > > > Values are
> > > > > > > +5:100 ??
> > > > > > > -5:50 ??
> > > > > > > -15:500 ??
> > > > > > > +15:400 ??
> > > > > > > +7.5:150 ??
> > > > > > > -7.5:180 ??
> > > > > > > +58: 7500 ??
> > > > > > > +130: 9000 ??
> > > > > > >
> > > > > > > these values are taken from a 2245A manual, but should not be
> > > > > > > very different on your scope. If one is significantly lower,
> > > > > > > check the related circuitry.
> > > > > > >
> > > > > > > The fan is not a sufficient load for the SMPS. When I make
> > > > > > > my trials, I use 2 4.7 ?? paralleled on the +5v.
> > > > > > > If the supply still ticks, try to disconnect the crowbar protection,
> > > > > > > or tie together the gate and the cathode of the SCR. Maybe some
> > > > > > > overvoltage due to a dying cap can fire it. Same recommendation
> > > > > > > about Q2208 (base tied to ground).
> > > > > > >
> > > > > > > --- In TekScopes@..., "Mover" wrote:
> > > > > > > >
> > > > > > > > Alas - if only it were that simple ...
> > > > > > > >
> > > > > > > > I finally fixed my SMPS and put it back into the chassis with only the main board. It runs in chirp mode - about every 1 sec there is a clicking sound - the secondary voltages rise and then something gets overloaded and the SMPS shuts down and then cycles again.
> > > > > > > >
> > > > > > > > I quickly disconnected power, isolated the SMPS and again verified that the SMPS is fine on its own with just the cooling fan load with a steady internal 44 VDC. No new or collateral damage thankfully.
> > > > > > > >
> > > > > > > > There are no obvious shorts on any of the supply lines on the main board. The issue may still very well be with the SMPS being unable to handle load even though the fan runs fine and the other voltages are fine.
> > > > > > > >
> > > > > > > > I assume that chirp mode is a common issue with these SMPS supplies. What have others done to (1) find whether the issue is with the SMPS or with the main board and if the latter, (2) which supply line or lines is drawing too much current and how to isolate the problem further?
> > > > > > > >
> > > > > > > > Thanks in advance.
> > > > > > > >
> > > > > > > > Priya.
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>

----- Original Message -----

From: nielsentelecom@...

To: TekScopes@...

Sent: Tuesday, February 19, 2013 12:10 PM

Subject: [TekScopes] Re: 2246 Mod A - no trace

?

Priya,

Wow, I didn't know it was all channels! Check your trigger setting, try a single shot too. maybe your focus is so far out you can't see it. Look at it in the dark too. Check the rejection section in the trigger area, set it for DC. Use the menu to set things to default just in case you got into unfamiliar territory. I don't see how putting in that socket would have done anything else barring you accidently damaged something in the process or zapped something that is static sensitive.

Pull back for a second. Hopefully you just overlooked something!

Nick Nielsen

--- In TekScopes@..., "Mover" wrote:
>
> Hi Nick,
>
> There is currently no trace on any of the channels after installing the IC socket at U174. However, the beam finder works as do all the menus and also the vertical time base cursors and readouts. I suspect something with the motherboard now at or near U174. Using your plan, I will apply an identical calibration signal to Ch2 and Ch3 and compare what happens to the signal using my R7704 as a test scope. More to come on this ...
>
> Yes, I will be careful as you say to not blow up something else along the way!
>
> Priya.
>
> --- In TekScopes@..., "nielsentelecom@" wrote:
> >
> > Priya,
> >
> > You could probably use ch3 to probe for the comparisons as a last resort on the following.
> >
> > I would set up identical conditions on both ch2 and ch1. then on ch 2 compare signal traces starting at the input. Place the same signal on both leads(channels). Check the U175 relay driver on ch2 and find out if any are high. You can also check the U171/U172 if your input to the U174/U175 does not match. But they appear to do different jobs on given pins. Probably best to test at the inputs of U174 & U175. Then go forward till you lose identical signal. Since you don't have U174 installed, just the socket instead, U171 may be calling for one of the relays in the Ch1 circuit to be pulled in or activated if you prefer. Then jumper where U174 should be on the affected driver. If as you say the relays are all operating as they should, you should expect the ch1 and ch2 relays to all align identically. It is possible one of the relays just isn't pulled in correctly. You can also check test point 1A (AT117 pin 7) in the ch1 circuit, and At127 pin 7 to ensure the they match once you get both attenuators aligned the same.
> >
> > Don't forget, BE CAREFUL! Don't blow up ch2!!
> >
> > Nick Nielsen
> >
> >
> > --- In TekScopes@..., "Mover" wrote:
> > >
> > > Update: I soldered an IC socket in U174 thinking that I would connect leads to it externally to diagnose the Ch1 issue and now the trace has completely disappeared! The beam finder works, but when I release the beam finder button, there is nothing on the screen other than the vert and hor selection displays. The menus are all fine and the time cursors work fine too - just no signal trace. Checked all the voltages and they are fine.
> > >
> > > I assume that I have to use another scope to trace the vertical amplifier area, but would appreciate any tips here - if the vertical amplifier was bad, would it not also affect the beam finder, displays and menus?
> > >
> > > Priya Jakatdar.
> > >
> > > --- In TekScopes@..., "Mover" wrote:
> > > >
> > > > I put the scope back together and it runs fine on Ch2, Ch3 and Ch4 including time & frequency measurements. All secondary voltages are well within the spec range (7.48V, -7.47V, 5.2V, -5.2V, 15.1V, -15.9V etc), so I have not made any adjustment to the 44VDC rail to avoid calibrating the scope from scratch. Will use it this way for now and let it run for some time to be sure nothing else is wrong or will fail before attempting further repair.
> > > >
> > > > The issue with Ch1 and voltage measurements is a charred U174 transistor relay driver IC (Intersil 3082) that appears to have caused the SMPS to fail in the first place. I have not replaced the chip thinking there may be a larger issue with or around U174. The Ch1 individual relays are all working fine (tested with a Kikusui constant-voltage constant-current supply) and drawing 25 mA or 12 mA according to their spec. When I do get some time later, I am thinking about validating the Shift Register output pins of U171 that drives U174 first and then maybe installing an IC socket rather than soldering a new U174.
> > > >
> > > > I have searched the archives and not found anything specific with respect to U174. Any thoughts or previous experience with this will be greatly appreciated.
> > > >
> > > > I want to thank everyone's help in getting my scope back into working condition. I have learned a lot about my 2246 and it is mainly because of you guys.
> > > >
> > > > Priya.
> > > >
> > > > --- In TekScopes@..., "Mover" wrote:
> > > > >
> > > > > Tom,
> > > > >
> > > > > I was only able to get enough time to assemble the SMPS into the chassis with just the main board and it runs fine - without the 40W series bulb:). The voltages are a bit off (5.28V, 7.46V etc) but I won't adjust anything till the proc board and the pot boards are in and providing normal operating load.
> > > > >
> > > > > That's for the weekend. More to come.
> > > > >
> > > > > Thanks for taking the time to make resistance measurements - very similar to mine.
> > > > >
> > > > > Priya.
> > > > >
> > > > > --- In TekScopes@..., "Tom Jobe" wrote:
> > > > > >
> > > > > > Hi Priya,
> > > > > > Resistances were taken on a nice working 2246 with a Fluke 110 which does not have enough voltage to forward bias the diodes.
> > > > > > I tried this Fluke meter on some standard diodes and some Schottky diodes and there was not much of a connection either way, just a little leakage depending on the polarity
> > > > > > There is not much difference from your readings, and no obvious indication of a problem on any of the voltages.
> > > > > > I will add my readings on to the end of your list.
> > > > > >
> > > > > > > +5:100 ?? - mine is 99 ohm - 106 ohm
> > > > > > > -5:50 ?? - mine is 41 ohm - 53 ohm
> > > > > > > -15:500 ?? - mine is 750 ohm - 590 ohm
> > > > > > > +15:400 ?? - mine is 583 ohm - 483 ohm
> > > > > > > +7.5:150 ?? - mine is 134 ohm - 152 ohm
> > > > > > > -7.5:180 ?? - mine is 143 ohm - 150 ohm
> > > > > > > +58: 7500 ?? - mine is almost open ( 8M ohm) - 2.5 M ohm? impossible to get a good reading
> > > > > > > +130: 9000 ?? - mine is 10,000 - 9000 ohm
> > > > > >
> > > > > > I guess the next step is to see what happens when you put the scope back together tonight.
> > > > > > tom jobe...
> > > > > >
> > > > > >
> > > > > >
> > > > > > ----- Original Message -----
> > > > > > From: Mover
> > > > > > To: TekScopes@...
> > > > > > Sent: Friday, January 04, 2013 12:20 PM
> > > > > > Subject: [TekScopes] Re: 2246 Mod A main board overloading the SMPS
> > > > > >
> > > > > >
> > > > > >
> > > > > > Tom & Francis,
> > > > > >
> > > > > > I discovered what it is - the ultra cautious in me had left a 40W light bulb in series with the isolation transformer secondary providing AC line power to the scope. It was there originally to prevent further collateral damage to the scope through my repair and testing. With any load exceeding the load provided by the fan, the SMPS pulls enough current through the light bulb that the AC line power to the scope drops below the 80V required to keep the SMPS running. This shuts down the SMPS and the 40W bulb comes on as the SMPS restarts - absolutely normal behavior. I had completely forgotten about the light bulb till this afternoon when I chanced to glance at it cycling with the SMPS and then I had an AHA moment!
> > > > > >
> > > > > > Regardless, I did measure resistances (with a Fluke 116 - don't own a meter recommended by TEK) and here they are:
> > > > > > > +5:100 ?? - mine is 99 ohm
> > > > > > > -5:50 ?? - mine is 41 ohm
> > > > > > > -15:500 ?? - mine is 750 ohm
> > > > > > > +15:400 ?? - mine is 583 ohm
> > > > > > > +7.5:150 ?? - mine is 134 ohm
> > > > > > > -7.5:180 ?? - mine is 143 ohm
> > > > > > > +58: 7500 ?? - mine is almost open ( 8M ohm)
> > > > > > > +130: 9000 ?? - mine is 10,000
> > > > > >
> > > > > > Other than the 58V resistance probably becuase my meter can't drive the diodes, my measurements looks fine.
> > > > > >
> > > > > > I ran it without the series light bulb and it happily drives a 10 ohm resistor from the 5V and regulation is excellent at 5.05 VDC. With the light bulb in series, it won't run anything more than the fan. Indeed, the fan is not sufficient load to test the SMPS.
> > > > > >
> > > > > > Believe I am ready to put the SMPS back into the scope tonight. I apologize to everyone who I misled with my earlier post on this and thanks as always for quick and thoughtful responses. You guys are great!
> > > > > >
> > > > > > Priya.
> > > > > >
> > > > > > --- In TekScopes@..., "Francis" wrote:
> > > > > > >
> > > > > > > Hi,
> > > > > > >
> > > > > > > several things:
> > > > > > >
> > > > > > > as Tom Jobe suggested, you can do the following:
> > > > > > > with the scope disconnected from the mains, check the resistances
> > > > > > > between ground and each supply. As Tek says, use an ohmeter that is able to forward bias diodes, usually a low range.
> > > > > > >
> > > > > > > Values are
> > > > > > > +5:100 ??
> > > > > > > -5:50 ??
> > > > > > > -15:500 ??
> > > > > > > +15:400 ??
> > > > > > > +7.5:150 ??
> > > > > > > -7.5:180 ??
> > > > > > > +58: 7500 ??
> > > > > > > +130: 9000 ??
> > > > > > >
> > > > > > > these values are taken from a 2245A manual, but should not be
> > > > > > > very different on your scope. If one is significantly lower,
> > > > > > > check the related circuitry.
> > > > > > >
> > > > > > > The fan is not a sufficient load for the SMPS. When I make
> > > > > > > my trials, I use 2 4.7 ?? paralleled on the +5v.
> > > > > > > If the supply still ticks, try to disconnect the crowbar protection,
> > > > > > > or tie together the gate and the cathode of the SCR. Maybe some
> > > > > > > overvoltage due to a dying cap can fire it. Same recommendation
> > > > > > > about Q2208 (base tied to ground).
> > > > > > >
> > > > > > > --- In TekScopes@..., "Mover" wrote:
> > > > > > > >
> > > > > > > > Alas - if only it were that simple ...
> > > > > > > >
> > > > > > > > I finally fixed my SMPS and put it back into the chassis with only the main board. It runs in chirp mode - about every 1 sec there is a clicking sound - the secondary voltages rise and then something gets overloaded and the SMPS shuts down and then cycles again.
> > > > > > > >
> > > > > > > > I quickly disconnected power, isolated the SMPS and again verified that the SMPS is fine on its own with just the cooling fan load with a steady internal 44 VDC. No new or collateral damage thankfully.
> > > > > > > >
> > > > > > > > There are no obvious shorts on any of the supply lines on the main board. The issue may still very well be with the SMPS being unable to handle load even though the fan runs fine and the other voltages are fine.
> > > > > > > >
> > > > > > > > I assume that chirp mode is a common issue with these SMPS supplies. What have others done to (1) find whether the issue is with the SMPS or with the main board and if the latter, (2) which supply line or lines is drawing too much current and how to isolate the problem further?
> > > > > > > >
> > > > > > > > Thanks in advance.
> > > > > > > >
> > > > > > > > Priya.
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>

Hi Nick,

There is currently no trace on any of the channels after installing the IC socket at U174. However, the beam finder works as do all the menus and also the vertical time base cursors and readouts. I suspect something with the motherboard now at or near U174. Using your plan, I will apply an identical calibration signal to Ch2 and Ch3 and compare what happens to the signal using my R7704 as a test scope. More to come on this ...

Yes, I will be careful as you say to not blow up something else along the way!

Priya.

--- In TekScopes@..., "nielsentelecom@" <nielsentelecom@> wrote:

Priya,

You could probably use ch3 to probe for the comparisons as a last resort on the following.

I would set up identical conditions on both ch2 and ch1. then on ch 2 compare signal traces starting at the input. Place the same signal on both leads(channels). Check the U175 relay driver on ch2 and find out if any are high. You can also check the U171/U172 if your input to the U174/U175 does not match. But they appear to do different jobs on given pins. Probably best to test at the inputs of U174 & U175. Then go forward till you lose identical signal. Since you don't have U174 installed, just the socket instead, U171 may be calling for one of the relays in the Ch1 circuit to be pulled in or activated if you prefer. Then jumper where U174 should be on the affected driver. If as you say the relays are all operating as they should, you should expect the ch1 and ch2 relays to all align identically. It is possible one of the relays just isn't pulled in correctly. You can also check test point 1A (AT117 pin 7) in the ch1 circuit, and At127 pin 7 to ensure the they match once you get both attenuators aligned the same.

Don't forget, BE CAREFUL! Don't blow up ch2!!

Nick Nielsen


--- In TekScopes@..., "Mover" <priya_jakatdar@> wrote:

Update: I soldered an IC socket in U174 thinking that I would connect leads to it externally to diagnose the Ch1 issue and now the trace has completely disappeared! The beam finder works, but when I release the beam finder button, there is nothing on the screen other than the vert and hor selection displays. The menus are all fine and the time cursors work fine too - just no signal trace. Checked all the voltages and they are fine.

I assume that I have to use another scope to trace the vertical amplifier area, but would appreciate any tips here - if the vertical amplifier was bad, would it not also affect the beam finder, displays and menus?

Priya Jakatdar.

--- In TekScopes@..., "Mover" <priya_jakatdar@> wrote:

I put the scope back together and it runs fine on Ch2, Ch3 and Ch4 including time & frequency measurements. All secondary voltages are well within the spec range (7.48V, -7.47V, 5.2V, -5.2V, 15.1V, -15.9V etc), so I have not made any adjustment to the 44VDC rail to avoid calibrating the scope from scratch. Will use it this way for now and let it run for some time to be sure nothing else is wrong or will fail before attempting further repair.

The issue with Ch1 and voltage measurements is a charred U174 transistor relay driver IC (Intersil 3082) that appears to have caused the SMPS to fail in the first place. I have not replaced the chip thinking there may be a larger issue with or around U174. The Ch1 individual relays are all working fine (tested with a Kikusui constant-voltage constant-current supply) and drawing 25 mA or 12 mA according to their spec. When I do get some time later, I am thinking about validating the Shift Register output pins of U171 that drives U174 first and then maybe installing an IC socket rather than soldering a new U174.

I have searched the archives and not found anything specific with respect to U174. Any thoughts or previous experience with this will be greatly appreciated.

I want to thank everyone's help in getting my scope back into working condition. I have learned a lot about my 2246 and it is mainly because of you guys.

Priya.

--- In TekScopes@..., "Mover" wrote:

Tom,

I was only able to get enough time to assemble the SMPS into the chassis with just the main board and it runs fine - without the 40W series bulb:). The voltages are a bit off (5.28V, 7.46V etc) but I won't adjust anything till the proc board and the pot boards are in and providing normal operating load.

That's for the weekend. More to come.

Thanks for taking the time to make resistance measurements - very similar to mine.

Priya.

--- In TekScopes@..., "Tom Jobe" wrote:

Hi Priya,
Resistances were taken on a nice working 2246 with a Fluke 110 which does not have enough voltage to forward bias the diodes.
I tried this Fluke meter on some standard diodes and some Schottky diodes and there was not much of a connection either way, just a little leakage depending on the polarity
There is not much difference from your readings, and no obvious indication of a problem on any of the voltages.
I will add my readings on to the end of your list.

+5:100 ?? - mine is 99 ohm - 106 ohm
-5:50 ?? - mine is 41 ohm - 53 ohm
-15:500 ?? - mine is 750 ohm - 590 ohm
+15:400 ?? - mine is 583 ohm - 483 ohm
+7.5:150 ?? - mine is 134 ohm - 152 ohm
-7.5:180 ?? - mine is 143 ohm - 150 ohm
+58: 7500 ?? - mine is almost open ( 8M ohm) - 2.5 M ohm? impossible to get a good reading
+130: 9000 ?? - mine is 10,000 - 9000 ohm

I guess the next step is to see what happens when you put the scope back together tonight.
tom jobe...



----- Original Message -----
From: Mover
To: TekScopes@...
Sent: Friday, January 04, 2013 12:20 PM
Subject: [TekScopes] Re: 2246 Mod A main board overloading the SMPS



Tom & Francis,

I discovered what it is - the ultra cautious in me had left a 40W light bulb in series with the isolation transformer secondary providing AC line power to the scope. It was there originally to prevent further collateral damage to the scope through my repair and testing. With any load exceeding the load provided by the fan, the SMPS pulls enough current through the light bulb that the AC line power to the scope drops below the 80V required to keep the SMPS running. This shuts down the SMPS and the 40W bulb comes on as the SMPS restarts - absolutely normal behavior. I had completely forgotten about the light bulb till this afternoon when I chanced to glance at it cycling with the SMPS and then I had an AHA moment!

Regardless, I did measure resistances (with a Fluke 116 - don't own a meter recommended by TEK) and here they are:
> +5:100 ?? - mine is 99 ohm
> -5:50 ?? - mine is 41 ohm
> -15:500 ?? - mine is 750 ohm
> +15:400 ?? - mine is 583 ohm
> +7.5:150 ?? - mine is 134 ohm
> -7.5:180 ?? - mine is 143 ohm
> +58: 7500 ?? - mine is almost open ( 8M ohm)
> +130: 9000 ?? - mine is 10,000

Other than the 58V resistance probably becuase my meter can't drive the diodes, my measurements looks fine.

I ran it without the series light bulb and it happily drives a 10 ohm resistor from the 5V and regulation is excellent at 5.05 VDC. With the light bulb in series, it won't run anything more than the fan. Indeed, the fan is not sufficient load to test the SMPS.

Believe I am ready to put the SMPS back into the scope tonight. I apologize to everyone who I misled with my earlier post on this and thanks as always for quick and thoughtful responses. You guys are great!

Priya.

--- In TekScopes@..., "Francis" wrote:
>
> Hi,
>
> several things:
>
> as Tom Jobe suggested, you can do the following:
> with the scope disconnected from the mains, check the resistances
> between ground and each supply. As Tek says, use an ohmeter that is able to forward bias diodes, usually a low range.
>
> Values are
> +5:100 ??
> -5:50 ??
> -15:500 ??
> +15:400 ??
> +7.5:150 ??
> -7.5:180 ??
> +58: 7500 ??
> +130: 9000 ??
>
> these values are taken from a 2245A manual, but should not be
> very different on your scope. If one is significantly lower,
> check the related circuitry.
>
> The fan is not a sufficient load for the SMPS. When I make
> my trials, I use 2 4.7 ?? paralleled on the +5v.
> If the supply still ticks, try to disconnect the crowbar protection,
> or tie together the gate and the cathode of the SCR. Maybe some
> overvoltage due to a dying cap can fire it. Same recommendation
> about Q2208 (base tied to ground).
>
> --- In TekScopes@..., "Mover" wrote:
> >
> > Alas - if only it were that simple ...
> >
> > I finally fixed my SMPS and put it back into the chassis with only the main board. It runs in chirp mode - about every 1 sec there is a clicking sound - the secondary voltages rise and then something gets overloaded and the SMPS shuts down and then cycles again.
> >
> > I quickly disconnected power, isolated the SMPS and again verified that the SMPS is fine on its own with just the cooling fan load with a steady internal 44 VDC. No new or collateral damage thankfully.
> >
> > There are no obvious shorts on any of the supply lines on the main board. The issue may still very well be with the SMPS being unable to handle load even though the fan runs fine and the other voltages are fine.
> >
> > I assume that chirp mode is a common issue with these SMPS supplies. What have others done to (1) find whether the issue is with the SMPS or with the main board and if the latter, (2) which supply line or lines is drawing too much current and how to isolate the problem further?
> >
> > Thanks in advance.
> >
> > Priya.
> >
>

Hi Victor,

Yes, I was referring specifically to a 2456B.

TEK specifications indicate that the automatic voltage reading is good
up to 1MHz. Interesting that you are seeing it function up to 200MHz.

Thanks.

Steve

On 2/18/2013 10:33 PM, victor_j_silva wrote:

I assume you mean a 2445A/65A/67 and 2445B/65B/67B.

I know the 24xx Digital Scopes have no such limit.

I just tried using a 1.2V sine wave and was able to measure pk-pk accurately to over 200MHz.

Maybe it depends on the signal amplitude.

--Victor

--- In TekScopes@..., Steve <steve65@> wrote:

Looking for confirmation of my understanding of the Tek specs for
automatic voltage measurement in the 2400 series scopes.

Am I right in understanding that automatic voltage measurement is
spec'ed to 1MHz? And that it is not spec'ed to function accurately above
1MHz?

That's what I get from my reading of the the catalog pages and the
service manual. Am I reading those documents correctly?

Thanks.

Steve

------------------------------------

Yahoo! Groups Links

Hi Mark,

I have not seen any Xeltec programmer over many years.

However, if I am allowed to make a recommendation: I can honestly recommend the products from batronix.com. I have their BX40, and it works like a charm.
Oh, I can see that they are a Distributor of Xeltec - interestingly enough...

Cheers,

Magnus

--- In TekScopes@..., "Mark Wendt (Contractor)" <mark.wendt@...> wrote:

Anybody familiar with the Xeltec line of programmers? Good, bad,
indifferent? I see a batch of 'em all the time on Ebay, some going for
seemingly high prices.

Thanks,
Mark

---

From: HankC
To: No Reply ; "TekScopes@..."
Sent: Tuesday, February 19, 2013 8:52 AM
Subject: [TekScopes] Re:DC504 counter display

I wasn't clear in describing my symptom.

5 of the 7 digits are OK; they display an "8" when you hold the reset button.

One digit has a bad center horiz segment; another digit has a bad top horiz segment.

Does that change anyone's diagnosis?

HankC

Anybody familiar with the Xeltec line of programmers? Good, bad,
indifferent? I see a batch of 'em all the time on Ebay, some going for
seemingly high prices.

Thanks,
Mark

Priya,

You could probably use ch3 to probe for the comparisons as a last resort on the following.

I would set up identical conditions on both ch2 and ch1. then on ch 2 compare signal traces starting at the input. Place the same signal on both leads(channels). Check the U175 relay driver on ch2 and find out if any are high. You can also check the U171/U172 if your input to the U174/U175 does not match. But they appear to do different jobs on given pins. Probably best to test at the inputs of U174 & U175. Then go forward till you lose identical signal. Since you don't have U174 installed, just the socket instead, U171 may be calling for one of the relays in the Ch1 circuit to be pulled in or activated if you prefer. Then jumper where U174 should be on the affected driver. If as you say the relays are all operating as they should, you should expect the ch1 and ch2 relays to all align identically. It is possible one of the relays just isn't pulled in correctly. You can also check test point 1A (AT117 pin 7) in the ch1 circuit, and At127 pin 7 to ensure the they match once you get both attenuators aligned the same.

Don't forget, BE CAREFUL! Don't blow up ch2!!

Nick Nielsen


--- In TekScopes@..., "Mover" <priya_jakatdar@> wrote:

Update: I soldered an IC socket in U174 thinking that I would connect leads to it externally to diagnose the Ch1 issue and now the trace has completely disappeared! The beam finder works, but when I release the beam finder button, there is nothing on the screen other than the vert and hor selection displays. The menus are all fine and the time cursors work fine too - just no signal trace. Checked all the voltages and they are fine.

I assume that I have to use another scope to trace the vertical amplifier area, but would appreciate any tips here - if the vertical amplifier was bad, would it not also affect the beam finder, displays and menus?

Priya Jakatdar.

--- In TekScopes@..., "Mover" <priya_jakatdar@> wrote:

I put the scope back together and it runs fine on Ch2, Ch3 and Ch4 including time & frequency measurements. All secondary voltages are well within the spec range (7.48V, -7.47V, 5.2V, -5.2V, 15.1V, -15.9V etc), so I have not made any adjustment to the 44VDC rail to avoid calibrating the scope from scratch. Will use it this way for now and let it run for some time to be sure nothing else is wrong or will fail before attempting further repair.

The issue with Ch1 and voltage measurements is a charred U174 transistor relay driver IC (Intersil 3082) that appears to have caused the SMPS to fail in the first place. I have not replaced the chip thinking there may be a larger issue with or around U174. The Ch1 individual relays are all working fine (tested with a Kikusui constant-voltage constant-current supply) and drawing 25 mA or 12 mA according to their spec. When I do get some time later, I am thinking about validating the Shift Register output pins of U171 that drives U174 first and then maybe installing an IC socket rather than soldering a new U174.

I have searched the archives and not found anything specific with respect to U174. Any thoughts or previous experience with this will be greatly appreciated.

I want to thank everyone's help in getting my scope back into working condition. I have learned a lot about my 2246 and it is mainly because of you guys.

Priya.

--- In TekScopes@..., "Mover" wrote:

Tom,

I was only able to get enough time to assemble the SMPS into the chassis with just the main board and it runs fine - without the 40W series bulb:). The voltages are a bit off (5.28V, 7.46V etc) but I won't adjust anything till the proc board and the pot boards are in and providing normal operating load.

That's for the weekend. More to come.

Thanks for taking the time to make resistance measurements - very similar to mine.

Priya.

--- In TekScopes@..., "Tom Jobe" wrote:

Hi Priya,
Resistances were taken on a nice working 2246 with a Fluke 110 which does not have enough voltage to forward bias the diodes.
I tried this Fluke meter on some standard diodes and some Schottky diodes and there was not much of a connection either way, just a little leakage depending on the polarity
There is not much difference from your readings, and no obvious indication of a problem on any of the voltages.
I will add my readings on to the end of your list.

+5:100 ?? - mine is 99 ohm - 106 ohm
-5:50 ?? - mine is 41 ohm - 53 ohm
-15:500 ?? - mine is 750 ohm - 590 ohm
+15:400 ?? - mine is 583 ohm - 483 ohm
+7.5:150 ?? - mine is 134 ohm - 152 ohm
-7.5:180 ?? - mine is 143 ohm - 150 ohm
+58: 7500 ?? - mine is almost open ( 8M ohm) - 2.5 M ohm? impossible to get a good reading
+130: 9000 ?? - mine is 10,000 - 9000 ohm

I guess the next step is to see what happens when you put the scope back together tonight.
tom jobe...



----- Original Message -----
From: Mover
To: TekScopes@...
Sent: Friday, January 04, 2013 12:20 PM
Subject: [TekScopes] Re: 2246 Mod A main board overloading the SMPS



Tom & Francis,

I discovered what it is - the ultra cautious in me had left a 40W light bulb in series with the isolation transformer secondary providing AC line power to the scope. It was there originally to prevent further collateral damage to the scope through my repair and testing. With any load exceeding the load provided by the fan, the SMPS pulls enough current through the light bulb that the AC line power to the scope drops below the 80V required to keep the SMPS running. This shuts down the SMPS and the 40W bulb comes on as the SMPS restarts - absolutely normal behavior. I had completely forgotten about the light bulb till this afternoon when I chanced to glance at it cycling with the SMPS and then I had an AHA moment!

Regardless, I did measure resistances (with a Fluke 116 - don't own a meter recommended by TEK) and here they are:
> +5:100 ?? - mine is 99 ohm
> -5:50 ?? - mine is 41 ohm
> -15:500 ?? - mine is 750 ohm
> +15:400 ?? - mine is 583 ohm
> +7.5:150 ?? - mine is 134 ohm
> -7.5:180 ?? - mine is 143 ohm
> +58: 7500 ?? - mine is almost open ( 8M ohm)
> +130: 9000 ?? - mine is 10,000

Other than the 58V resistance probably becuase my meter can't drive the diodes, my measurements looks fine.

I ran it without the series light bulb and it happily drives a 10 ohm resistor from the 5V and regulation is excellent at 5.05 VDC. With the light bulb in series, it won't run anything more than the fan. Indeed, the fan is not sufficient load to test the SMPS.

Believe I am ready to put the SMPS back into the scope tonight. I apologize to everyone who I misled with my earlier post on this and thanks as always for quick and thoughtful responses. You guys are great!

Priya.

--- In TekScopes@..., "Francis" wrote:
>
> Hi,
>
> several things:
>
> as Tom Jobe suggested, you can do the following:
> with the scope disconnected from the mains, check the resistances
> between ground and each supply. As Tek says, use an ohmeter that is able to forward bias diodes, usually a low range.
>
> Values are
> +5:100 ??
> -5:50 ??
> -15:500 ??
> +15:400 ??
> +7.5:150 ??
> -7.5:180 ??
> +58: 7500 ??
> +130: 9000 ??
>
> these values are taken from a 2245A manual, but should not be
> very different on your scope. If one is significantly lower,
> check the related circuitry.
>
> The fan is not a sufficient load for the SMPS. When I make
> my trials, I use 2 4.7 ?? paralleled on the +5v.
> If the supply still ticks, try to disconnect the crowbar protection,
> or tie together the gate and the cathode of the SCR. Maybe some
> overvoltage due to a dying cap can fire it. Same recommendation
> about Q2208 (base tied to ground).
>
> --- In TekScopes@..., "Mover" wrote:
> >
> > Alas - if only it were that simple ...
> >
> > I finally fixed my SMPS and put it back into the chassis with only the main board. It runs in chirp mode - about every 1 sec there is a clicking sound - the secondary voltages rise and then something gets overloaded and the SMPS shuts down and then cycles again.
> >
> > I quickly disconnected power, isolated the SMPS and again verified that the SMPS is fine on its own with just the cooling fan load with a steady internal 44 VDC. No new or collateral damage thankfully.
> >
> > There are no obvious shorts on any of the supply lines on the main board. The issue may still very well be with the SMPS being unable to handle load even though the fan runs fine and the other voltages are fine.
> >
> > I assume that chirp mode is a common issue with these SMPS supplies. What have others done to (1) find whether the issue is with the SMPS or with the main board and if the latter, (2) which supply line or lines is drawing too much current and how to isolate the problem further?
> >
> > Thanks in advance.
> >
> > Priya.
> >
>

----- Original Message -----

From: Chris

To: TekScopes@...

Sent: Tuesday, February 19, 2013 4:52 AM

Subject: [TekScopes] Re: Tektronix 2465 capacitors etc.

?

I had sent a response earlier but it didn't appear to have made it.

I checked some of the voltages on the board, but can't say I entirely know what to make of all of them (newb alert again hah)

Ok, I've got 94v on the unregulated rail
On the op-amp, pin 1 vref is 10.00v Pin 2 from the voltage divider is reading as ~1v or just under. Pin 1 is reading 15.19v.

Q1222: Emitter 8v, base is grounded of course, and 11.6v on the collector.

Q1220: (sorry, not sure which is emitter/base/collector, I'd have to look up a datasheet - more newb showing through). So looking down on the power supply as it's mounted in the chassis: 11.3v on the left pin, 94.7v on the middle pin (must be the collector) and 11.8v on the right pin.

Q1221: 94v on the collector, 11.1v on the base and 10.6v on the emitter.

I didn't measure Q1223 - hard to reach that one.

R1212: 94v on the unregulated rail side, 10.5v on the other side of it.
R1220: 94v on the unregulated rail side, 9v on the other side.

Curious how I got 15.19v on pin 1 of U1281A with a 10v ref and a 1v comparison from the voltage divider off the regulated line - looking at the datasheet it looks like it should be operating as two separate op-amps with one half regulating the 87v line and the other the 42v line, so I fired it up again and checked the voltage on all of it's pins:

pin 1: 15.57v
pin 2: 1.05v
pin 3: 10.00v
pin 4: -6.86v
pin 5: 10.00v
pin 6: 1.58v
pin 7: 15.58v
pin 8: 16.42

So thinking about it for a bit, the schematic shows a voltage of -1.53v for pin 1 (a far cry from the 15v I'm getting)which I assume is the voltage I should see when the line is regulated to 82v. And I assume then that the 16.42v is the positive power for U1281, and the -6.86v is the supply that lets it pull Q1222 low when the voltage from the voltage divider feeding pin 2 = the 10v ref from pin 3.

So I guess I learned something, but as far as using the voltages to give me an indication as to what's gone wrong I'm not sure. That will take a better man (or woman) that's more educated than I! I would have to resort to the shotgun repair method at this point - replace all the components :) (certainly not to the point of wanting to shoot the scope yet lol)

As a note, when reading these voltages they can vary a bit while checking them. Sometimes it's not uncommon to see some of the voltages vary ~0.5v it seems, so that accounts for some of the variance in the first vs 2nd measurements in areas. Earlier I was reading ~9.5v on the 87v regulated line, but tonight it was just under 9v.

Thanks!
Chris

--- In TekScopes@..., "John Snyder" wrote:
>
> Chris
>
> The CR1244 is across the B-E junction of the transistor, so in circuit it
> would not measure Open like a diode out of the circuit would.
>
> I have my board out waiting for the inverter board to dry from it's
> cleaning, and I measure .706V forward (of the diode) and .581V reverse
> (instead of open, which is forward for the transistor junction.)
>
> You could measure all the voltages Q1220, Q1221, Q1222, and Q1224 E,B and C
> along with U1281A pin 1, 2 and 3 CR1220 anode to see what is out of wack
>
> John
>
>
>
> -----Original Message-----
> From: TekScopes@... [mailto:TekScopes@...] On Behalf
> Of Chris
> Sent: Monday, February 18, 2013 8:37 PM
> To: TekScopes@...
> Subject: [TekScopes] Re: Tektronix 2465 capacitors etc.
>
> John,
> A HUGE thank you on checking that and giving me your value! I was hoping
> the short wasn't in the main board somewhere as that doesn't look like fun
> to pull in the least.
>
> I just checked the resistance from the pin 7 (blue 87v wire) on the
> connector (power supply still out and on the bench) and I got a value of
> 25.55Kohm, so it would appear I should be OK to go at that (assuming that
> powering something else up on the main board doesn't cause it to
> short/overload the supply). I was testing the diodes on the power supply
> and diode CR1244 is giving me 0.538V forward and 0.630v reverse. I think I
> might pull it and check it out of the board later tonight after I eat etc.
>
> Thanks for the help!
> Chris
>
> --- In TekScopes@..., "John Snyder" wrote:
> >
> > Chris
> >
> > The problem could be in the 87V regulator
> >
> > Or
> >
> > Their could be a short/low Resistance some where in the load
> >
> > I have a 2465B open and I measured a load resistance of 25.3K to ground on
> > Pin 7 of J121 (87V, the blue wire) with the power supply unplugged from
> the J121 connector
> > unit
> >
> > John
> >
> > -----Original Message-----
> > From: TekScopes@... [mailto:TekScopes@...] On
> Behalf
> > Of Chris
> > Sent: Sunday, February 17, 2013 5:40 PM
> > To: TekScopes@...
> > Subject: [TekScopes] Re: Tektronix 2465 capacitors etc.
> >
> > All voltages measured in the scope with everything hooked up. I just got
> > done checking the voltages pre-regulator.
> >
> > At J233A I get:
> > pin 5 (87v unregulated) 97.6v
> > Pin 3 (42v unregulated) 49.0v
> >
> > And at J234A I get:
> > pin 5 (15v unregulated) 18.94v
> > Pin 4 (5v unregulated) 6.64
> > Pin 2 (-5v unregulated) -6.92v
> > Pin 1 (-15v unregulated) -18.54v
> >
> > Based on the unregulated values, I believe the issue must lie in the
> > regulator portions, and since I'm getting the 97.6v pre-regulated it would
> > seem to me the voltage doubler is working. I also double checked and
> > verified the 10v reference voltage at the test point on the main board as
> > well as the J121 connector that feeds the main board. (I figured this was
> > important to double check as the regulators all are based off the 10v
> > reference as I read it). Of course this is where I wish to learn more - I
> > understand what the individual components do but I still somewhat struggle
> > to see what the assembly as a whole is doing, which is why I'm trying to
> get
> > into all this, so maybe my understanding is skewed. :)
> >
> > At any rate, it would seem to me that with the unregulated voltages where
> > they're at, that the issue would have to lie within the follow area:
> >
> >
> > Yes? No? I mean I have the correct voltages on the left side of those
> three
> > groups, and the wrong voltages on the right side, so it would seem that's
> > where I should look next?
> >
> > Thanks for helping this newb out!
> >
> > Chris
> >
> >
> > --- In TekScopes@..., "Tom Miller" wrote:
> > >
> > > The +87 is from a doubler and added to the +42. I would take a close
> look
> > at the three 10 uF caps and all the diodes in that area. Be sure to only
> use
> > fast diodes for any replacements.
> > >
> > > Since you recapped this unit, don't overlook the fact that bad
> capacitors
> > can come from the factory new. Did you measure all these voltages in the
> > scope or on an external load?
> > >
> > >
> > >
> > >
> > > Regards,
> > > Tom
> > >
> > >
> >
> >
> >
> > ------------------------------------
> >
> > Yahoo! Groups Links
> >
>
>
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>

640 ohms ought to be enough for anyone.

--- In TekScopes@..., "Philip" <ndpmcintosh@...> wrote:

I recently obtained a batch of old and diverse probes. Many are junk but a few are rather interesting. Out of a number of old 1x Tek probes I should be able to put together 2 nice ones (as soon as a get a hex wrench small enough).

Another I have studied is an old Fairchild that is in good condition that has a resistance of 640 ohms end to end on the center conductor. To what use could one put to such a probe?