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" <tmiller11147@> 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

> >
> > 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?
> >
>

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: Don Black

To: TekScopes@...

Sent: Monday, February 18, 2013 10:35 PM

Subject: Re: [TekScopes] T935A seized pots help

?

I have a T912 which had tight controls on the brightness and something else (focus?). I managed to free them up a bit but they need more TLC. These pots are located back inside the scope with plastic shafts running from the knobs to the pots. I'm not sure if it's the pots are tight or the shafts in the front panel bushings. These bushes release with a snap action by pulling the shaft forward; it's detailed in the manual which warns considerable force may be required. I'm worried about aging plastic breaking if I try to remove them. I intend to try some lubricant as a first step. I hadn't considered deoxit, have you found that effective on plastic? I was going to try isopropyl alcohol first, then perhaps some oil. I've had success with silicon lubricant on plastic if you can get it into the bearing. Are the pots you're dealing with mounted on the front panel or remotely like mine. Please keep posting on your progress. I have also considered the plastic might have swollen slightly, any thoughts?
The T912 is a storage scope and a in a brief trial I couldn't seem to get it to store, but I may not have been holding my mouth right. Have to read the instructions again. Nice little scope.

Don Black.

On 19-Feb-13 8:11 AM, Tom Miller wrote:

?

I would try to put a little thin oil down the shaft. Take the knobs off and just apply a drop or two to the shaft and allow it to soak in for a while. It may take a few applications to break it free.

?

?

Tom

?

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

From: Andrew

To: TekScopes@...

Sent: Monday, February 18, 2013 3:44 PM

Subject: [TekScopes] T935A seized pots help

?

Hi,

First posting on this group, hope someone can help....

I have a T935A scope which has developed a problem and I'd like to try and fix it as its a very useful portable scope.

Basically two of the front panel variable pots, the Y2 axis variable and the X axis variable have seized solid. Y1 seems okay.

So before I strip the scope down, which looks to be quite a job to get the relevant pcbs out, has anybody come across this before?

Is there much hope that I can fix the existing pots or do they need to be replaced (any suggestions for good suppliers that will ship to the UK?).

Many thanks,

Andrew

?

I would try to put a little thin oil down the shaft. Take the knobs off and just apply a drop or two to the shaft and allow it to soak in for a while. It may take a few applications to break it free.

?

?

Tom

?

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

From: Andrew

To: TekScopes@...

Sent: Monday, February 18, 2013 3:44 PM

Subject: [TekScopes] T935A seized pots help

?

Hi,

First posting on this group, hope someone can help....

I have a T935A scope which has developed a problem and I'd like to try and fix it as its a very useful portable scope.

Basically two of the front panel variable pots, the Y2 axis variable and the X axis variable have seized solid. Y1 seems okay.

So before I strip the scope down, which looks to be quite a job to get the relevant pcbs out, has anybody come across this before?

Is there much hope that I can fix the existing pots or do they need to be replaced (any suggestions for good suppliers that will ship to the UK?).

Many thanks,

Andrew

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

640 ohms ought to be enough for anyone.

--- In TekScopes@... <mailto:TekScopes%40yahoogroups.com>, "Philip" 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?

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

No virus found in this message.
Checked by AVG - www.avg.com <>
Version: 10.0.1430 / Virus Database: 2639/5614 - Release Date: 02/18/13

?

?

While the comments are valid for 454, the 454A (as listed in the subject) does have a larger screen and FET input circuitry.?? So, if Frank truly has a 454A available its more of a level playing field to compare.
??
Having lived and carried a 453 for many??years, my first encounter with a 465 was to always adjust the Focus and Astigmatism controls to get a sharp trace; until I went on line and learned what TEK had done to the CRT.??????
??
To Paul's point, indeed it is very handy (sometimes mandatory) to have a second scope to use when the first gets into problem.??. . .?? but indeed [BE Warned] it does tend to get out of hand very very quickly! I started with a non TEK scope, found a 453 at St Vincent's thrift, eBayed 465s, 453A, 454A, 464. . . .
??Denis
??


________________________________
From: "wa2mze@..." <wa2mze@...>
To: TekScopes@...
Sent: Monday, February 18, 2013 12:28 PM
Subject: [TekScopes] Re: 454A vs 465B Recommendation

??
I also own both a 465 and a 454. The 454 has a smaller screen and 50% greater BW. However in tests I very recently made, both scopes would display and (barely) trigger on a 200mhz signal from a GDO. The 465 series does not focus as sharp as the 454/453, this is a CRT design issue, Tek sacrificed spot size for brightness, screen size, and writing speed on the newer tubes. The difference is small IMHO and not worth fussing over.

The 454/453 may use common parts, though the Nuvistor triodes in the front end are becoming as expensive and hard to find as 1L6's for Trans-Oceanics. (TV 13CW4's *might* sub). They ARE harder to fix, in some cases you have to completely disassemble the things to get at the area you need to work on. I recently fixed the channel 1 variable pot which had become "ganged" with the V/D switch due to gunk between the shafts. I was able to reach the Allan screw to loosen the inner shaft at the pot with a long hex key. To reach the same on channel two might have required pulling the CRT and shield!

453/454 scopes rarely needed replacement CRT's compared to the 465 series. The techs working in the Metrology lab at Gould CSD where I used to work told me they had purchased spare CRT's for all the 454 and 465/475 scopes they owned. They nearly used up all of the spares for the 465/475 scopes, but still had almost all of the spares in unopened boxes for the 454's. This was years later when they were finally selling off these scopes to buy newer ones. BTW I bought my 454 from Gould when they auctioned them off to the employees. I also got a set of probes and a cart out of the deal. (The idiots threw out the spare tubes before I could get my hands on one!).

If you need to use the scope in XY mode (like for a curve tracer such as the Heath IT-1121) the 465 is a better choice with a "sane" xy mode and larger screen. The 465 is a little lighter and easier to carry than the 454 if that matters.

--- In mailto:TekScopes%40yahoogroups.com, Paul Amaranth wrote:

I have both a 465 and a 453.

The trace might be a little crisper on the 454 and the controls might be a little larger.

But from using both, I'd get the 465b and look for a parts mule for the day when repair is needed.

BTW, since you're looking at that genre of instruments, you'll also need a second scope to
fix the first one when it breaks. In the FWIW department, it's OK to stop at 2, you don't
have to become like us. Or is it 3 with the parts mule? And so the slippery slope starts ...

On Mon, Feb 18, 2013 at 04:25:44PM -0000, Frank Edwards wrote:

I have an opportunity to get either a 454 or 465. Spec wise, either will meet my need, both are working and there is no difference in cost. From what I have read, the 454 contains no proprietary parts and can therefore be repaired using common off-the-shelf parts, vs the 465 which has some proprietary parts but is newer. It seems to me there are many more 465s available, but I have not been looking for any particular part. My intent is to get a scope that will not become economically unrepairable because of availability of repair parts. In summary, from a reliability and repairability perspective, which should be the better option?

--
Paul Amaranth, GCIH | Rochester MI, USA
Aurora Group, Inc. | Security, Systems & Software
paul@ | Unix & Windows

?

?

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.
> >
>

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?