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2465B SN 55xxx with TEST 05 FAIL 40

tekscopegroup@...
 

Error comes up after power up. Also lots of jitter on traces that eventually end up moving downwards off the screen.

From what I read elsewhere might be related to well known leaking capacitor problem on the A5 board affecting the DAC ref voltage area just bellow the offending caps? (I hope!)

Any opinions? BTW rear label indicates only Option 49 installed, but so far cant find any reference to this particular option number.
Maybe this indicated several individual combined options where installed?

Any pointers appreciated.

tekscopegroup@...
 

On Tue, Oct 9, 2018 at 01:08 PM, <tekscopegroup@...> wrote:

BTW rear label indicates only Option 49 installed, but so far
cant find any reference to this particular option number.
Maybe this indicated several individual combined options where installed?

Any pointers appreciated.
CORRECTION: Option 46 is the correct number.

Chuck Harris
 

Among possibly other things, you need to clean up your A5
card, replace the SMD electrolytic capacitors, replace the
two 10K SMD resistors that are in the DAC reference circuit,
and maybe repair a few etched through traces.

You can prove out my hypothesis by looking at the solder joints
on the various parts of the A5 board (component side). They
should be shiny like little mirrors. If any are dull looking,
possibly milky white, there is electrolyte damage.

First clean in soapy water, use a tooth brush to scrub, and
then dry.

Next mechanically remove (scrape) any corrosion build up on the
4 SMD electrolytic capacitor's solder joints... down to fresh
solder.

If you don't do this, the joints will have to be overheated
to get the solder to melt, and the pads will break free
of the board... They may anyway, but this is your best hope.


Now the tricky stuff. If you over heat the joints, they
will come free of the board. If you apply *any* mechanical
pressure when hot, the pads will tear free of the board.

My preferred method is to use an IR under board preheater set
for about 100C, and use a pair of desoldering tweezers to
remove the capacitors whole. Keep the tweezer's temperature
low, about 320C at most. Test by sliding, not lifting the
capacitor. When the solder melts, you will feel it give way
under the tweezer points, then just slide the capacitor off
the pads. BE GENTLE!

If you use a preheater, please remove the plastic standoffs
from the bottom side of the board... no need to risk melting
them.

A secondary method for the tool deficient, is to use a pair
of sharp diagonal cutters, and cut the capacitors at their
case crimp. Don't allow the cutters to put much, if any, force
on the board. Then pick off the remains of the capacitor until
you have nothing left but two little "L" shaped wires that are
the capacitor's leads. BE GENTLE!

Use a tweezer and a soldering iron to remove the "L" shaped wires,
one at a time, and re tin the pads. 300C to 320C soldering iron.
BE GENTLE!

After the board is free of bad parts, and the pads are tinned,
wash it again with warm water and dish soap, and a tooth brush.

Dry in a convection oven at 50C for a couple of hours, and the
solder on the new parts. Don't skip this wash, electrolyte will
be under the old parts, and you don't want to trap it under the
new.

I solder in new SMD capacitors, but using a soldering iron. The
capacitors today are good... as were the old... the leaky electrolyte
problem was caused by overheating when the boards were in the
reflow oven... Some say it was caused by using the wrong solvent
to clean up flux... It could be either. I vote for over heating.

Any questions, just ask.

If you want the work done for you, contact me off list.

-Chuck Harris

tekscopegroup@... wrote:

Error comes up after power up. Also lots of jitter on traces that eventually end up moving downwards off the screen.

From what I read elsewhere might be related to well known leaking capacitor problem on the A5 board affecting the DAC ref voltage area just bellow the offending caps? (I hope!)
Any opinions? BTW rear label indicates only Option 49 installed, but so far cant find any reference to this particular option number.
Maybe this indicated several individual combined options where installed?

Any pointers appreciated.



tekscopegroup@...
 

Hi Chuck,

Thank you for the very detailed input on the procedures. I've been reading up on this A5 board bad caps situation and have found similar good tips and information. In any case I hope the corrosion will not be that severe, but who knows given the symptoms. Guess I'll find out once the scope gets to me in what I hope will be about 2 weeks if all goes well. In any case I feel confident and have experience with SMD soldering using a fine tip conventional iron, which in this case would have been my choice as well to solder the new caps in to keep it simple. Also, if I am not wrong its really 5 SMD capacitors that need to be replaced on the A5 board, 4 on one side of the board, and another one on of the opposite corners I think?

Much appreciate the tips on heating cautions on the corroded pads, and definitively the sliding and not lifting the caps seems to make a lot of sense to further protect the board from heat delamination. Always a good thing to heed to the voice of experience, specially on Tek equipment this nice that would be a shame to ruin just because of a bad soldering technique.

One question comes to mind: when you say "wash it again with warm water and dish soap, and a tooth brush", once all the affected pads are clean and tinned, do you mean to wash the whole affected area and then just rinse off with water? Guess there are no parts nearby that can be damaged by the water. In other situations sometimes I had good results cleaning up residual corrosion on a board by using 70% alcohol and a soft toothbrush. I had to redo the cleaning/scrubbing process several times. Advantage of alcohol is that it will evaporate quickly, and much less water will be left behind in comparison to using dish soap and plain water throughout the cleaning process. But then of course this was a very different kind of board, only two layers, low density, etc. So if you could please elaborate a bit about the washing/rinsing procedure.

I've worked so far on three other Tek scopes, a 2247A, a 222, and a 2213A. The 2213A was my first scope repairing experience back around 2004-ish (power supply issues/bad T948 against all odds). Back then it took a me a while to troubleshoot that devilish inverter power supply, but with quite a bit of help from the amazing Dennis Cobley, and Dean Smith fedexing me a donated almost complete main board with the needed transformer, in the end that humble scope came back to life. But when it comes to a 2465B, which is a classic and must have, I consider myself a rookie at best. But I digress...

Thanks again.
-Alex

Chuck Harris
 

Hi Alex,

No, it is only 4 electrolytic capacitors. There are
a couple of tantalums, but leave them alone.

I mean put the board in the kitchen sink, put an inch
of warm to hot water in the sink, and a good squirt of
Dawn, or other detergent, and scrub the area around the
capacitors with a toothbrush. That is the only way I
have found that will really clean up the leaked electrolyte.

The electrolyte goes everywhere, and spreads as fumes, so
it will be both above and below the capacitors when they
are in the position they were in when the leak occurred.

If you must use alcohol, the 70% is best, though 50% would
be better. The electrolyte is a polar compound, and will
only dissolve in a polar solvent, like water. It will not
dissolve at all in 99% IPA, as there is no water, and alcohol
is not polar enough.

If you are worried about water infiltration into the pots,
you can put a piece of electrical tape over them, but I
haven't found that to be necessary. Shake the board dry,
and them put it in a convection oven. Nothing else will
be bothered by the water in the least bit.

Do not try to remove the capacitors as complete units if you
are going to use a single point soldering iron. That is
virtually guaranteed to destroy the board. Cut them apart.

-Chuck Harris


tekscopegroup@... wrote:

Hi Chuck,

Thank you for the very detailed input on the procedures. I've been reading up on this A5 board bad caps situation and have found similar good tips and information. In any case I hope the corrosion will not be that severe, but who knows given the symptoms. Guess I'll find out once the scope gets to me in what I hope will be about 2 weeks if all goes well. In any case I feel confident and have experience with SMD soldering using a fine tip conventional iron, which in this case would have been my choice as well to solder the new caps in to keep it simple. Also, if I am not wrong its really 5 SMD capacitors that need to be replaced on the A5 board, 4 on one side of the board, and another one on of the opposite corners I think?

Much appreciate the tips on heating cautions on the corroded pads, and definitively the sliding and not lifting the caps seems to make a lot of sense to further protect the board from heat delamination. Always a good thing to heed to the voice of experience, specially on Tek equipment this nice that would be a shame to ruin just because of a bad soldering technique.

One question comes to mind: when you say "wash it again with warm water and dish soap, and a tooth brush", once all the affected pads are clean and tinned, do you mean to wash the whole affected area and then just rinse off with water? Guess there are no parts nearby that can be damaged by the water. In other situations sometimes I had good results cleaning up residual corrosion on a board by using 70% alcohol and a soft toothbrush. I had to redo the cleaning/scrubbing process several times. Advantage of alcohol is that it will evaporate quickly, and much less water will be left behind in comparison to using dish soap and plain water throughout the cleaning process. But then of course this was a very different kind of board, only two layers, low density, etc. So if you could please elaborate a bit about the washing/rinsing procedure.

I've worked so far on three other Tek scopes, a 2247A, a 222, and a 2213A. The 2213A was my first scope repairing experience back around 2004-ish (power supply issues/bad T948 against all odds). Back then it took a me a while to troubleshoot that devilish inverter power supply, but with quite a bit of help from the amazing Dennis Cobley, and Dean Smith fedexing me a donated almost complete main board with the needed transformer, in the end that humble scope came back to life. But when it comes to a 2465B, which is a classic and must have, I consider myself a rookie at best. But I digress...

Thanks again.
-Alex

Siggi
 

On Tue, 9 Oct 2018 at 22:20 <tekscopegroup@...> wrote:

I've been reading up on this A5 board bad caps situation and have found
similar good tips and information.
You should probably just change those SMD caps on sight. If you want to
conclusively trace the wandering traces to the DAC reference, you can do
that by measuring the 1.36 and -1.25 reference voltages on the A5 board.
Those should be spot-on and pure DC, if they wobble around as the traces
move, then you know the DAC reference is compromised.
If you don't see those wobble around with the traces, it means you have
other and/or additional problems.

It's also useful to measure those voltages after your repair to validate
that you've brought the DAC in spec.

tekscopegroup@...
 

Right you are, only 4 SMD problem caps total. I need to have the board in front of me for facts to start falling in place. Definitively will carefully chop apart the caps before attempting removal. I did not intend to disturb any tantalums, unless really necessary. I've also read that the 20K trimmer pot near the DAC sometimes gets also damaged and needs to be replaced before the ref voltages are correct again. Maybe just order it too along the caps, just in case.

Your cleaning procedure makes a lot of sense, something I've not seen explained in detail anywhere else. Usually one would cringe at the idea of splashing water on a board like this, but now I am reassured it will be the best thing to do, even if corrosion damage appears to be light (due to fumes spreading on all nearby surfaces) its worth doing it right.

Do you by any chance know what Option 46 would be for this scope? Its the only field on the rear panel that has a punched hole in it.

Thanks.

Tom Gardner
 

My technique, which I used to replace the capacitors and one SMD resistor in the middle of the others, was:

* play a soldering station's hot air gun over the relevant component until the
solder melts and it blows away (do a few experiments to see which
temperature/velocity works best, and use a narrow nozzle)
* protect the surrounding components by loosely covering them with
kapton/polyimide adhesive tape, to deflect the hot air away
* clean the pads etc by any means you choose; I used IPA
* dab solder paste on the pads
* place replacement components, using solder paste as an "adhesive"
* use hot air gun to reflow that component
* remove polyimide tape

On 10/10/18 17:02, tekscopegroup@... wrote:
Right you are, only 4 SMD problem caps total. I need to have the board in front of me for facts to start falling in place. Definitively will carefully chop apart the caps before attempting removal. I did not intend to disturb any tantalums, unless really necessary. I've also read that the 20K trimmer pot near the DAC sometimes gets also damaged and needs to be replaced before the ref voltages are correct again. Maybe just order it too along the caps, just in case.

Your cleaning procedure makes a lot of sense, something I've not seen explained in detail anywhere else. Usually one would cringe at the idea of splashing water on a board like this, but now I am reassured it will be the best thing to do, even if corrosion damage appears to be light (due to fumes spreading on all nearby surfaces) its worth doing it right.

Do you by any chance know what Option 46 would be for this scope? Its the only field on the rear panel that has a punched hole in it.

Thanks.

Chuck Harris
 

Tektronix wrote high option numbers, like OPT46, to show things,
like including 4 probes, when they usually only included 2, or
including a carry pouch, or adding a Japanese mains power cord,
..., stuff like that.

Other options were mnemonic to what the option provided, like
OPT14 being for P14 phosphor on some scopes.

However, I don't see 46 listed in any of the literature I have.

-Chuck Harris

tekscopegroup@... wrote:

Right you are, only 4 SMD problem caps total. I need to have the board in front of me for facts to start falling in place. Definitively will carefully chop apart the caps before attempting removal. I did not intend to disturb any tantalums, unless really necessary. I've also read that the 20K trimmer pot near the DAC sometimes gets also damaged and needs to be replaced before the ref voltages are correct again. Maybe just order it too along the caps, just in case.

Your cleaning procedure makes a lot of sense, something I've not seen explained in detail anywhere else. Usually one would cringe at the idea of splashing water on a board like this, but now I am reassured it will be the best thing to do, even if corrosion damage appears to be light (due to fumes spreading on all nearby surfaces) its worth doing it right.

Do you by any chance know what Option 46 would be for this scope? Its the only field on the rear panel that has a punched hole in it.

Thanks.



 

Option 46 is the designation for the military version of the scope (OS-288/G) that included option 10 IEEE-488 interface and 2 probes.

Manuel