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

From: Chris

To: TekScopes@...

Sent: Saturday, February 23, 2013 3:20 AM

Subject: [TekScopes] Re: Tektronix 2465 capacitors etc. - Going deeper!

?

Looking through the schematics, it seems there's not much the 87v supply runs - mostly listed to capacitors/resistors here and there, but I found that it also supplies and runs the infamous U800. Now I can't help but worry about the fact that they go hand in hand may allude to incredibly bad luck at losing the U800 chip within 3-4 hours of purchasing the scope. Or maybe I'm just disappointed and all doom and gloom.. heh It's just looking like a pretty good coincidence!

Chris

--- In TekScopes@..., "Chris" wrote:
>
> Ok, I think it's time to dig deeper!
>
> Thank you Tom for your suggestions. Since I wasn't having any luck with the board, I replaced all of the 2N5551 transistors for the 87 volt supply. The old ones tested OK so I didn't hold my breath for much to change - which it didn't. So the next thing I did was lift Q1223 and power it up - Progress! (sort of) The front panel did not lock up with all of the LED's on as I was having, and I could get all 4 traces to show up on the screen and move their vertical positions around. I could not however get any horizontal trace movement or even horizontal position adjustment. The readout at the bottom was also compressed into just a fuzzy vertical little line.
>
> I replaced Q1223 with another new transistor, as well as diode CR1244 (tested good as well) and I verified the values of R1222 and R1223 for the current overload transistor.
>
> So, it would now appear I've been chasing my tail with a regulator problem, where in fact I must have a problem somewhere else that's overloading supply? The fact that I couldn't get any horizontal adjustment or reading on the scope leads me to believe it's a function of the horizontal aspect of the scope. This ties in with the failure mode I had of the scope when in use - my display compressed horizontally and the readout at the bottom was just a fuzzy line. When I powered it off and back on it went to the locked up boot up I've been diagnosing.
>
> So now I feel like I'm right back at the beginning with nothing gained but a new set of caps and a bit of knowledge (not a bad thing).
>
> As a side note, I've always had a tabletop fan pointed at the scope's main board during tests. So it shouldn't have overheated during testing, and I've never had it on for more than 5 minutes at a crack to check voltages etc. Where do I go from here?
>
> Chris
>
>
>
> --- In TekScopes@..., "Tom Miller" wrote:
> >
> > Change Q1222. It should be full off and the collector should be up around 90 volts or so. However, Q1223 could also be pulling that line down so change it also. You could lift the collector of Q1223 and see if the supply comes up just to rule that out. Also (2), is R1212 ok? If it were open, the same issue would be there.
> >
> > Tom
> >
> >
> >
> >
> > ----- 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
> >
> >
>

After installing the socket, I did an ohmmeter test on all connections to the socket from other chips and they are all fine. By default (no voltage applied), the input selection relay selects GND, so it should still show the trace. Ch2, Ch3 and Ch4 were working before I installed the socket, so it is baffling.

It does show "Self check Volts Cal error" (this is new) and also complains about the battery not working correctly (this error was there before).

With the beam finder on, it shows a very bright horizontal line display with some vertical deflection at the center of the screen. Believe that is how it is supposed to work.

I will pull back and see if somehow the front panel controls are far off somehow, though that would not result in a Volts Cal error. Something is not good with the motherboard near the repair - the same something that caused the failure to begin with.

Priya.


--- In TekScopes@..., "Tom Miller" <tmiller11147@> wrote:

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.
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>

Thanks for that Mark. Another tool in the box.

Dave

Sent from my iPhone



On Feb 22, 2013, at 10:46 AM, "mark101234" <mhb55@...> wrote:

I am not sure how many people are aware of Oil of Wintergreen penetrating properties, so I though I would point it out. Oil of wintergreen is very wet,it will creep into very close fits.

I have used it to free up stuck set screws in knobs, a few drops down the hole and let it sit for an hour and the screw will come right out.

Some pots when new had damping grease applied to the shaft/bushing area, as they age they become very difficult to turn. Two or three drops of Oil of Wintergreen in the shaft/bushing area and let it sit over night, positioned to let the oil run down the shaft and the pot will turn like new.

Synthetic Oil of Wintergreen does not seem to work as well as the real stuff. The real stuff is not cheep, .5 fl.oz. is about $7.00. It can be had at Drug stores and good cooking stores. A bottle lasts me about 10 years.

Oil of Wintergreen appears to be very inert I have not had it affect rubber or any plastics,unlike some commercial products. I am not sure about it's long term lubrication properties, it may be a good idea to follow it up with an oil.

I hope this proves as useful to others as it has been to me, besides the gear smells nice afterward.
Mark Bradley K6TAF

?

> It is all in the 067-0645-02 Extender Cable Document which can be found on
> the Ebaman site. 17/20 AWG and 28/34 AWG are the Wire Gauges. In case
> you don't want to subscribe I can send you the pdf-document. Please
> respond directly.

I've searched ebaman for this - but draw a blank for the p/no or extender as
search terms.

Craig

I am not sure how many people are aware of Oil of Wintergreen penetrating properties, so I though I would point it out. Oil of wintergreen is very wet,it will creep into very close fits.

I have used it to free up stuck set screws in knobs, a few drops down the hole and let it sit for an hour and the screw will come right out.

Some pots when new had damping grease applied to the shaft/bushing area, as they age they become very difficult to turn. Two or three drops of Oil of Wintergreen in the shaft/bushing area and let it sit over night, positioned to let the oil run down the shaft and the pot will turn like new.

Synthetic Oil of Wintergreen does not seem to work as well as the real stuff. The real stuff is not cheep, .5 fl.oz. is about $7.00. It can be had at Drug stores and good cooking stores. A bottle lasts me about 10 years.

Oil of Wintergreen appears to be very inert I have not had it affect rubber or any plastics,unlike some commercial products. I am not sure about it's long term lubrication properties, it may be a good idea to follow it up with an oil.

I hope this proves as useful to others as it has been to me, besides the gear smells nice afterward.

Mark Bradley K6TAF

Good point! I wasn't really thinking. They likely are mostly silver

since they tarnished black. Nickel will probably go greenish (or

perhaps that's from the copper underneath that oxidize on a couple

connectors I have).

If the concern with the Tarnex is removing it, at least on the

adaptors I can sonicate them in warm water and that should be

effective in removing the solution after a couple rinses.

Dan

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

*From:* "bonddaleena@ aol.com" bonddaleena@ aol.com>

*To:* TekScopes@yahoogrou ps.com

*Sent:* Friday, February 22, 2013 3:42 PM

*Subject:* Re: [TekScopes] Cleaning nickel-plated adapters and input

connectors? Magic formula?

Hi Dan. On all the TE I have, the connectors appear to be Silver

plated. You could (!) carefully clean them with "Tarnex" liquid. Then

clean off that stuff with Windex, etc.

Most of the time, I simply give then a quick brushing with a stainless

steel detail brush, which looks like a toothbrush.

ron

N4UE

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

From: Daniel Koller kaboomdk@yahoo. com>

To: TekScopes TekScopes@yahoogrou ps.com>

Sent: Fri, Feb 22, 2013 3:33 pm

Subject: [TekScopes] Cleaning nickel-plated adapters and input

connectors? Magic formula?

Hi folks,

I am sure this has been asked before, so please point me to the

correct links if so. A quick search of the archives didn't find

anything easily.

How does one clean t he nickel-plated adapters and input connectors

of old scopes? I am thinking of two situations here. The first is

the BNC or UHF connectors on the panels of the scopes, that cannot be

easily removed. The second case is things like BNC T's and BNC to UHF

adapters and the like which are small and can be completely dipped in

some cleaning solution.

I have a number of adapters and connectors where the nickel is

getting black, and they are filthy. I would Ideally like to deoxidize

them so they come out shiny and new. Some sort of chemical dip or a

series of washes would be preferred, where I can keep the amount of

physical scrubbing required to a minimum. I envision perhaps

scrubbing once with a toothbrush (maybe with tooth paste?), wrinsing

in an ultrasonic bath, then dipping them in some magic formula that

shines them up. Connectors on the scope would have to be brushed and

washed in-situ.

The question is, what is the magic formula?

Thanks.

Dan

I just received a 2465b and it seemed fine on my initial check. However, after leaving it on for several minutes, the readout and display started to drift up and down. At times, the top of the readout was off the screen.

I spent a few minutes searching but didn't find any other posts describing a similar issue. I'll keep looking.

I'm going to open it and check all the voltage rails and look for leaky caps.

Does this problem ring a bell with anyone? Any hints or pointers?

Thanks,

-Scott

I would start looking on schematic 6 since the vertical drift affects

everything. If it is a failure in U600 or U400 then there is not much

to be done but there are other possible.

The channel switch digital inputs which select what to display, VS1

through VS4, might not be switching all of the way.

The vertical centering signal into pin 39 of U600 might be drifting. I

would disconnect the dynamic centering and then adjust the vertical

and horizontal centering adjustment and see how that changes things.

Do all 4 input channels work over the full vertical range of the CRT

without any non-linearity?

On Fri, 22 Feb 2013 14:34:35 -0700, Scott Harris

scottrharris@ gmail.com> wrote:

I just received a 2465b and it seemed fine on my initial check. However, after leaving it on for several minutes, the readout and display started to drift up and down. At times, the top of the readout was off the screen.

I spent a few minutes searching but didn't find any other posts describing a similar issue. I'll keep looking.

I'm going to open it and check all the voltage rails and look for leaky caps.

Does this problem ring a bell with anyone? Any hints or pointers?

Thanks,

-Scott

My trusty 2465B now has a vertically offset display on the CRT. The bottom of the normal display is now at mid-point. Has anyone seen and solved this problem? Where do I look for the source of this problem?

Thanks, AL

?

Hi to All,

It is all in the 067-0645-02 Extender Cable Document which can be found on the Ebaman site. 17/20 AWG and 28/34 AWG are the Wire Gauges. In case you don't want to subscribe I can send you the pdf-document. Please respond directly.

Greetings,

Egge Siert

Interesting.
Does it say "WARNING 80V on Center Conductor" above the SMA like it does on the GR874 ones?
Does it look like there was a larger hole for a GR874 where the SMA is?

Dennis

Mine has an SMA for the charge line. But that is in addition to an internal charge line.

Craig

Ok, I think it's time to dig deeper!

Thank you Tom for your suggestions. Since I wasn't having any luck with the board, I replaced all of the 2N5551 transistors for the 87 volt supply. The old ones tested OK so I didn't hold my breath for much to change - which it didn't. So the next thing I did was lift Q1223 and power it up - Progress! (sort of) The front panel did not lock up with all of the LED's on as I was having, and I could get all 4 traces to show up on the screen and move their vertical positions around. I could not however get any horizontal trace movement or even horizontal position adjustment. The readout at the bottom was also compressed into just a fuzzy vertical little line.

I replaced Q1223 with another new transistor, as well as diode CR1244 (tested good as well) and I verified the values of R1222 and R1223 for the current overload transistor.

So, it would now appear I've been chasing my tail with a regulator problem, where in fact I must have a problem somewhere else that's overloading supply? The fact that I couldn't get any horizontal adjustment or reading on the scope leads me to believe it's a function of the horizontal aspect of the scope. This ties in with the failure mode I had of the scope when in use - my display compressed horizontally and the readout at the bottom was just a fuzzy line. When I powered it off and back on it went to the locked up boot up I've been diagnosing.

So now I feel like I'm right back at the beginning with nothing gained but a new set of caps and a bit of knowledge (not a bad thing).

As a side note, I've always had a tabletop fan pointed at the scope's main board during tests. So it shouldn't have overheated during testing, and I've never had it on for more than 5 minutes at a crack to check voltages etc. Where do I go from here?

Chris



--- In TekScopes@..., "Tom Miller" <tmiller11147@> wrote:

Change Q1222. It should be full off and the collector should be up around 90 volts or so. However, Q1223 could also be pulling that line down so change it also. You could lift the collector of Q1223 and see if the supply comes up just to rule that out. Also (2), is R1212 ok? If it were open, the same issue would be there.

Tom




----- 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

Change Q1222. It should be full off and the collector should be up around 90 volts or so. However, Q1223 could also be pulling that line down so change it also. You could lift the collector of Q1223 and see if the supply comes up just to rule that out. Also (2), is R1212 ok? If it were open, the same issue would be there.

Tom




----- 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

?

I¡¯m looking for a solution to cleaning up and restoring to usable condition printed circuit boards and their electronic components that were subjected to the electrolyte from a leaking NiCd battery.

?

One person suggested the supermarket product ¡°CLR¡± (Calcium/Lime/Rust manufactured by Jelmar). It does seem to clean off some of the corrosion but I have no idea what the long term effects of the CLR are on the electronics.

?

Dennis