EEVblog Electronics Community Forum

Electronics => Repair => Topic started by: jonpaul on January 29, 2017, 12:44:03 pm

Title: TEK 2467B Odd failure
Post by: jonpaul on January 29, 2017, 12:44:03 pm
Hello all: Just got a TEK 2465B, SN>B050...., seems to be in good condition, and works for about 2 minutes.   

Then, even with no input, the relays click, it displays 50 Ohm Overload and the display becomes unstable and then fades off, regardless of intensity setting.   

It is consistent every time it is started. No errors on the startup self test.

I suspect a power supply issue or perhaps a failing tantalum cap causing power overload or short after it warms up.

Anyone ever seen such behavior? Any troubleshooting tips?

MANY THANKS

Jon
Title: Re: TEK 2467B Odd failure
Post by: tggzzz on January 29, 2017, 01:39:28 pm
Is it a 2465b or 2467b?

Anyway, look at the caps and other components on the control board near the DAC; there are many guides to this, so I won't repeat them poorly.

Also look at the mains X/Y rated filter caps; replace them if they are crazed before they detonate a series resistor and the PCB prepreg. Again, there is an extremely explicit pdf of how to do that.

Don't forget that if operating out of the case, you will need to arrange for external airflow over the hybrids and other ICs.
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on January 29, 2017, 03:40:46 pm
Hi there many thanks for the fast response.

Yes 2467B.

The readouts seem stable issue affects  only the trace intensity. Each time it blanks out, moving the intensity control up a bit brings the traces back for a few seconds, then they fade out again. The 50 Ohm Overload /relays clicking has not occured again.

I have opened it up and checked for the A5 SMD caps failure, they seem undamaged. The HV board visually seems OK.

I now suspect either the intensity pot/FP mux or a fault in the Z-axis circuit.

Next stop: Pull off PSU cover and see if any caps are leaking, and check all LV PSU voltages.

Any further input is appreciated.

With Kind Regards,



Jon

Title: Re: TEK 2467B Odd failure
Post by: tggzzz on January 29, 2017, 04:19:20 pm
Always check the voltages for value and ripple; ripple indicates higher ESR, which can be independent of capacitance.

If it is like the 2445/2465, then you can look at the output of the single DAC directly, and also the caps used to store the demultiplexed voltage.
If those voltages are stable, then consider the LT version of the Z-axis voltage waveform, and whether the DC restorer is working correctly.

Without checking, I would assume that the overload relay threshold is directly or indirectly dependent on the DAC output.

The LT Z axis waveforms are relatively "safe". The action of the DC restorer is to translate the voltage changes up to the CRT cathode's voltage, i.e. 2.5-2kV => less safe :)

I have, on a 465 and with a great deal of care, managed to use a DC voltmeter to measure the mean DC and mean AC value of  Vgk directly. First test was to check that the mean  DC Vgk was suitable for ensuring blanking and brightness.  Next I noted that changing the mean AC value of the LT Z axis waveform by 10% changed the mean AC value of Vgk by 10%, implying that the DC restorer was working OK. In my case the problem was a detached wire inside the CRT itself.
Title: Re: TEK 2467B Odd failure
Post by: WaveyDipole on January 29, 2017, 06:12:41 pm
I have something like this on my old Tek 465. It would run for a couple of minutes and then the display would fade away. Turn it off, and then back on a again and the trace would be back for a while and then disappear again.

It turned out to be a faulty metal can capacitor on on the -8v line. It would seem that the cap was shorting internally upon warming up. There was no external sign of a problem. The line would go from -8v to zero which affected all circuits dependent on it. I did also find a shorted tantalum cap, but this appeared to be unrelated. Replacement of the can resolved the problem but only for a short while until the rectifier bridge failed. Evidently the fault on the old cap had taken its toll on the rectifier as well. With both replaced, the scope has been fine so far.

I know we are dealing with a different and more modern scope here so the problem may be entirely different, but I thought I'd mention it for what its worth.
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on January 29, 2017, 08:19:20 pm
Hello again:

1, PSU volatge and ripple are fine, I checked at the main board PS 14 pin header, J119, everything is within spec.

2, At the Z Azis test point, I can see the upper waveform peaks unstable and jumping as the trace brightness fluctuates.

3, Any intensity control setting lasts for just a few seconds, then the traces fade out.

4, Readout intensity is not affected.

It is either an input to U950 the Z axis hybrid, or the hybrid itself.

Again, any assistance is appreciated!

Kind Regards,

Jon
Title: Re: TEK 2467B Odd failure
Post by: tggzzz on January 29, 2017, 09:25:49 pm
The manual will describe how the intensity is controlled.

Look at any relevant DAC output voltages. Follow them through the circuit.

The correct readout intensity makes it likely that u950 is ok.
Title: Re: TEK 2467B Odd failure
Post by: MarkL on January 30, 2017, 07:32:14 pm
Does the trace appear momentarily no matter if you turn the intensity up or down?

The DAC output for the display intensity is on U2630 pin 7 ("DIA"), as tggzzz suggests.

If that isn't behaving, you could check that the display intensity ("DI") signal into the ADC is ok.  That's on U2501 pin 2 and should vary smoothly from 0 to 1.36V as you turn the intensity knob.

All the DAC output holding capacitors are being refreshed continuously, so it's odd that the intensity fades only after a change.

Maybe a 10 second video of the problem would help.
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on January 30, 2017, 07:39:52 pm
Hi there: The DIA and DI signals are indeed affected. To clarify, the intensiy is normal for a few seconds, then either fades out OR entire display becomes unstable. After the fade out, if you move the front panel control to a new setting the sequence repeats.

With the entire display becoming unstable, and occasionally getting the 50 Ohm Input Overload message (with no inputs) I stared to check all power more carefully. Yet all power voltage and ripple seem to be normal. I inspected for any leaky tantalum SMD power bypass caps, all seem intact and none overheating as failed tants often do.



Finally I have the QService 2465B/2467B manual, for SN > B050.

BUT the A5 control board seems different so I cannot even trace the signals further.

Any assistance will be appreciated.

I will try to make a video of the issue. 


Many thanks again!

Jon
Title: Re: TEK 2467B Odd failure
Post by: tautech on January 30, 2017, 07:46:48 pm
You might find this can offer some guidance:
http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf (http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf)
Title: Re: TEK 2467B Odd failure
Post by: MarkL on January 30, 2017, 08:52:05 pm
Hi there: The DIA and DI signals are indeed affected. To clarify, the intensiy is normal for a few seconds, then either fades out OR entire display becomes unstable. After the fade out, if you move the front panel control to a new setting the sequence repeats.

With the entire display becoming unstable, and occasionally getting the 50 Ohm Input Overload message (with no inputs) I stared to check all power more carefully. Yet all power voltage and ripple seem to be normal. I inspected for any leaky tantalum SMD power bypass caps, all seem intact and none overheating as failed tants often do.
The DI and 50ohm overload circuits all come into the ADC.  It could be that the input multiplexing is having issues.

We should first confirm the signals coming into the ADC are stable.

DI comes into one side of R2702 before it goes to U2501 pin 2.  Is the DI signal stable on the other side of R702?  You can also use P512 pin 29 if you can't get to R2702.

If you look at the Ch1 and Ch2 overload signal inputs on U2601 pins 15 and 12, are those unstable also?  How about on P511 pins 5 and 2 which is before their ADC input resistors?


When you say the display is "unstable", what do you mean?

I'm looking at schematics for SN > B050.  If you think there's a mismatch for your serial number, a picture of your board could be helpful.
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on January 31, 2017, 02:36:04 pm
Hello again:

Attached are photos: The A5 board, the display first seconds, afterwards and same sequence if intensity pot is changed.

The BIG issue: The A5 boards are not as in the QService and all other 2465B/2467B manuals for SN over B050! Mine is B050878,


Mine has NO separate backup battery, the Dallas NV RAM, and uses almost all 74HC logic rather than 4051, etc! So the A5 schematics and board layout are totally different! I have another with the exact same A5 board type.

So rather hard to continuer troubleshooting.

Does anyone have the A5 sch and PCB placement for this version?

Again, any assistance is appreciated!

With Kind Regards,

Jon


Title: Re: TEK 2467B Odd failure
Post by: MarkL on January 31, 2017, 04:09:38 pm
Does anyone have the A5 sch and PCB placement for this version?
I've been looking at "Tek 2465B 2467B service OCR with schematics":

  http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=Tektronix/Tektronix_-_2465B_Oscilloscope (http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=Tektronix/Tektronix_-_2465B_Oscilloscope)

There are two of them, named slightly different.  They're identical.

There are separate pages for SN >= B050000, and SN < B049999.  You're board certainly looks like SN >= B050000.  A spot check on a few chips also matches.

The scan isn't the greatest, but it's readable.  If you want a really good version, you could buy a PDF copy from artekmanuals.com.  Their manuals are professionally scanned, and inexpensive for what you get.
Title: Re: TEK 2467B Odd failure
Post by: MarkL on January 31, 2017, 04:20:50 pm
Hi there: The DIA and DI signals are indeed affected. To clarify, the intensiy is normal for a few seconds, then either fades out OR entire display becomes unstable. After the fade out, if you move the front panel control to a new setting the sequence repeats.
I just re-read this.

To clarify:  When you say "affected", do you mean that DI and/or DIA smoothly tracks the intensity control when you turn it, or does the voltage drop over a few seconds by itself (or possibly appear erratic)?

We should try to find the earliest point where we can observe a correlation with the fading.  And not forgetting about the overtemp and relay clicking.  It's very likely something in common to all.
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on January 31, 2017, 04:29:52 pm
Hi there MarkL: WOW! Great link,

Perfect, YES in the REVISIONS at the end IS the exact board and schematic I have for A5.  I had somehow assume the QService Greece printed manual I had was perfect. But it has NO revisions at all!

This is a big help. The scans are fine.

Notes: 1. Check intensity pot at FP, perfect 0 - 1.36VDC. It seems to go from the FP connector on the main board A1 across to the connectors linking to A5 Control.

2, When "unstable" I get a fading trace, it moves vertically and comes back if I move the intensity pot.

I will try to take more photos, after I dig into the schematics.

Affected: The DI seem to be very odd, with pulses and the baseline jumping about. BUT I am not 100% sure I was probing the correct resistors and IC pins. I will check more carefully and try to get more photos.

The entire thing is so odd, as the PSU seems fine but 3 symptoms happen at one, always with a few seconds delay. A real mystery.

Many thanks again! Back to work!

Cheers,

Jon


Title: Re: TEK 2467B Odd failure
Post by: jonpaul on January 31, 2017, 06:15:39 pm
Hello again MarkL!

Many thanks for these better schematics, you have linked me to,


Now I can see that intensity controld from FP,  RDI and DI are fine, exactly as expected DC controlled by the FP pots.

 These signals flow thru R2701 and R2702, and appear at the MUX, pins 2,5 of U2501.

Looking at the MUX output, again all is normal, I see the MUX signal, and the levels at the corresponding time slots vary as you move the pots.

Thus the problem lies after the MUX but before the Z axis circuity.

I think that board A5 is OK.

Again any further clews are appreciated.

Kind Regards,

Jon
Title: Re: TEK 2467B Odd failure
Post by: MarkL on January 31, 2017, 10:06:24 pm
...
Looking at the MUX output, again all is normal, I see the MUX signal, and the levels at the corresponding time slots vary as you move the pots.

Thus the problem lies after the MUX but before the Z axis circuity.

I think that board A5 is OK.
...
Well, I wouldn't go that far yet.  I'm assuming you're saying the problem is continuing to happen while DI looks fine.

There's a lot between the ADC MUX output and the Z-axis drive.  Such as the ADC, the processor, and the DAC, for starters.  The processor reads the position of the intensity knob, alters the value as needed, and spits it back out via the DAC.

Are you ready to take a look at DIA: U2630 pin 1?  This is the intensity output from the DAC after the processor is done with it.  (Note: I said pin 7 before; I guess I wasn't zoomed in enough.  Sorry about that...)

Actually, before you look at that, start up the Exerciser Routine #1 (on page 6-15) and poke around with it a bit.  This is reads the various pots on the front panel and prints out their value after conversion by the ADC.  It also includes the DAC output value.  See if you see anything of interest there while turning the intensity pot.
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on February 01, 2017, 03:06:04 pm
Hello again MarkL! Many thanks again for your expert assistance!

Before I follow-up on your very fine suggestions, a few  more clews:

0. Both RO and min intensity pots have correct voltages measured at the pot terminals.

1, Readouts are rock solid and intensity is behaving normally as you turn the FP knob.
Since both readout intensity and display intensity follow parallel paths, its odd this affects one but not the other.

2, The symptom happens regardless of use of SWP A, SWP B or both.

3, There seems to be a loss of beam current control, as you can turn intensity way up before it fades out to zero.

Perhaps some clews here?

I will continue later today,

Cheers,

Jon

Title: Re: TEK 2467B Odd failure
Post by: jonpaul on February 01, 2017, 04:35:08 pm
Dear MarkL: I just checked:

1/ Exer 01: Yes perfect in intensity, the hex codes vary as expected and are stable. All other controls operate normally in this test.

2/ DIA: U2630 pin 1: Sure, the  DAC intensity signal is bad:

About 5..6 V DC (with mux noise) when intensity is set to be visible. Varies with control setting.

After the few seconds and the trace fades out, it lowers to 3V, with no mux noise. As soon as you move the control and get a trace again, the exact same behavior at U2630 pin 1.

The similar signal for readout intensity is fine.

Best,


Jon
Title: Re: TEK 2467B Odd failure
Post by: MarkL on February 01, 2017, 10:34:48 pm
I'm beginning to wonder about one of the the DAC muxes, U2530, or the control inputs to it.  The reason is that you said the trace moves vertically when the fade problem is happening.  U2530, among other things, is responsible for the trace vertical position.

So, you first could take a look at U2630 pin 3 (connected to U2530 pin 2).  This is the input to the opamp from the holding cap which eventually is output on U2630 pin 1.  If U2630 is ok, you should see this input tracking the problem too.

Does the vertical movement happen at the same time as the fade on all the channels?  Or just a particular channel or subset of channels?  Can you confirm that the voltage change is happening on U2530 pins 12, 13, 14, and/or 15?  These are the vertical position outputs for Ch4, Ch1, Ch2, Ch3, respectively.

U2530 has control input signals that are in common to the other DAC mux, U2521.  Take a look at U2521 pin 2.  See if this is moving with the fade problem.  Probably not, but interesting if it is.

You could also take a look at U2530 pin 6.  This is the mux inhibit signal.  It probably has some periodicity to it, but for now just check to make sure the logic levels are sane (<0.7 V or >2.1V).  You should also check the select inputs U2530 pins 9, 10, 11 to see if they're sane too.

Also check TP2420 (+1.36V) and TP2421 (-1.25V).  These control the DAC reference voltage.  From your other observations these should be stable, but let's make sure.
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on February 01, 2017, 11:29:05 pm
WOW! Yes I did notice the vertical trace position wandering when the traces start to fade!

I will follow up on your great suggestion later tonight or Thursday!


Again, many thanks!


Jon
Title: Re: TEK 2467B Odd failure
Post by: james_s on February 01, 2017, 11:49:39 pm
What about the DAC reference voltage? Is it external to the DAC?
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on February 02, 2017, 12:06:19 am
 U2630 pin 3 (connected to U2530 pin 2).

YES I see the  input tracking the problem 


  U2530 pins 12, 13, 14, and/or 15?  vertical position outputs for Ch4, Ch1, Ch2, Ch3,

YES I see the instability on these pins

U2530 has control input signals that are in common to the other DAC mux, U2521.  Take a look at U2521 pin 2.  See if this is moving with the fade problem. 


IT IS OK

You could also take a look at U2530 pin 6.  This is the mux inhibit signal. 


OK 

 U2530 pins 9, 10, 11 to see if they're sane too.


OK

Also check TP2420 (+1.36V) and TP2421 (-1.25V).  Cannot find these! On parts list but not on schematic or PCB layout.


Whats next?


Thanks Again!

Jon
Title: Re: TEK 2467B Odd failure
Post by: MarkL on February 02, 2017, 01:54:32 am
...
Also check TP2420 (+1.36V) and TP2421 (-1.25V).  Cannot find these! On parts list but not on schematic or PCB layout.
I must have flipped over to the SN < 49999 schematic for a second.  The TP's on that page.  But you can pick up +1.36V on J511 pin 24, and -1.25V on J511 pin 15.  They should be ok, but it's good to check.

If you want to check the Vref for the DAC as james_s mentions that's on pin 14 and 15 of U2101.  Just check for stability.  All other indications say they should be fine too, but I'm never against being sure.  When troubleshooting it's always an ordered list of probabilities and never absolutes.

Quote
Whats next?
We need to figure out if U2530 is working.

I assume you have another scope you've been using to look at things.  What kind of equipment do you have?

To take a first pass at this, I would trigger the scope on the rising edge of the inhibit input on U2530 pin 6.  Then probe any of the outputs DI or CHx position that are unstable during the problem and look at pin 6 and any of those outputs at the same time.

No outputs should be moving during inhibit high (all the mux output switches should be disconnected).  If any of the outputs moves during inhibit high, U2530 is dead.  I suppose you should also verify it has power on pins 8 (Gnd) and 16 (+5V).

The converse is not necessarily true.  If nothing moves, it doesn't mean it's ok.  We can still test for that, but it's going to need fancier triggering (pattern trigger).

The 50ohm overload problem is still a concern.  The DAC in this unit is also the ADC when combined with comparator U2510.  It's a very busy DAC.  If one of the DAC muxes is misbehaving it could affect the ADC.  Just a theory at this point.
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on February 02, 2017, 12:30:46 pm
Hello Mark:

Yes I have a very extensive lab, TEK 2465B, 2467B, 2467, 7104, 7704, etc plus about 100 plugins including some rare ones. Also 2 pcs Yokogawa DL7704 with logic probes. ( a 40 yrs collection of stuff!)

So I can do a pattern trigger test and save it.

1, Will follow-up today on all your new suggestions.

2, The 50 Ohm OV symptom happened only occasionally, with no inputs, you get the warning as relays click. Only happens during the intensity fault.

More news soon!

Enjoy,


Jon


Title: Re: TEK 2467B Odd failure
Post by: jonpaul on February 02, 2017, 02:04:28 pm
Hello Mark: Indeed the refs at 14 and 15 of U2101 are unstable, fluctuating ~ 0.124....0.136V.

The Refs are also fluctuating, the  +1.36V on J511 pin 24, and -1.25V on J511 pin 15.

Finally there is a 10V REF  bus nearby U2101, bypassed by SMD tant, C2010.



Q+WOW! VERY unstable ~ 7.5..8.15V with dips much lower!

The plot thickens. Perhaps a failing SMD tant, overloading this critical reference?

Cheers,

Jon
Title: Re: TEK 2467B Odd failure
Post by: MarkL on February 02, 2017, 02:53:09 pm
Ok, let's chase that.  All bets are off if we have the power supply bouncing around.  Is it jumping on its own without turning the intensity knob?

Previously you had checked the output of the intensity pot and saw no instability there.  That is simply a wiper between the +1.36V rail and ground.  Which should have said the +1.36V supply was ok (it's the same +1.36V that you're looking at on J511 pin 24).  But I'll bet that's not stable now too.

Could be a failing cap, but let's track this backwards and see what we can find.

You had already checked the power supply voltages.  Are any of those unstable at J119 (as per table 5-1)?  It includes the +10V supply.  (Note: Table 5-1 is in the cal section.  I wouldn't try to adjust anything at this point.)
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on February 02, 2017, 03:03:41 pm
Hello Mark: Indeed the refs at 14 and 15 of U2101 are unstable, fluctuating ~ 0.124....0.136V.

The Refs are also fluctuating, the  +1.36V on J511 pin 24, and -1.25V on J511 pin 15.

Finally there is a 10V REF  bus nearby U2101, bypassed by SMD tant, C2010.



Q+WOW! VERY unstable ~ 7.5..8.15V with dips much lower!

The plot thickens. Perhaps a failing SMD tant, overloading this critical reference? How to distinguish a problem in the 10V ref loads and bypasses vs at the 10V Ref power ckt?

Cheers,

Jon
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on February 02, 2017, 04:26:38 pm
Mark! WELL......

at J119, all bulk power seems OK, BUT -1.25 and + 1.25 are fluctuating around the normal values.

The 10.00 REF is fine there, BUT I still see it lower and fluctuation on A5 at C2010! Clews are accumuclationg! How can it be good at J119 and bad at the A5 board?

YIKES!

Enjoy,


Jon
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on February 02, 2017, 04:28:01 pm
Forgot: YES the unstable levels occur regardless of intensity control.
j
Title: Re: TEK 2467B Odd failure
Post by: MarkL on February 02, 2017, 04:55:09 pm
Mark! WELL......

at J119, all bulk power seems OK, BUT -1.25 and + 1.25 are fluctuating around the normal values.

The 10.00 REF is fine there, BUT I still see it lower and fluctuation on A5 at C2010! Clews are accumuclationg! How can it be good at J119 and bad at the A5 board?

YIKES!

Perhaps you have a bad connection on J251?  It's rather convoluted, but according to diagram #13 it comes right from the regulator board (also shown on schematic #12, location 4B).  The 10V ref is on pins 15 and 16 for the A5 board. 

The J119 +10V ref is it's own connection from the regulator board.

EDIT/ADD: J119 is on schematic #11.  I really hate these schematics with separate power distribution diagrams.  It's really obfuscated.

EDIT/MORE: The +10V ref makes its way onto the A1 board via J121 pin 3 (diagram #10, location 1N).  From there it goes to the J119 test connector.  (If anything, I'm posting this so I don't have to figure out the path again.)
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on February 02, 2017, 05:16:53 pm
Hi Mark: I pulled and reseated J251, no easy way to probe it. Looking at the 10V ref at C2010, and flexing the cable at both ends, no effect. The voltage fluctuates about 8.5V. Yes at J119 on main board, I get a solid 9.99V!

Really confusing.

Jon

Title: Re: TEK 2467B Odd failure
Post by: MarkL on February 02, 2017, 05:19:38 pm
You could try a temporary jumper between J119 where the +10V ref is good, and the purported +10V ref connection on C2010.

With the unit off you could also check the resistance between those two points.
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on February 02, 2017, 05:37:51 pm
Hi: It seems to have a stable 1.113 K between J119 pin 4 and C2010 + side. Again very odd!

Jon
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on February 02, 2017, 05:54:16 pm
Mark!

I checked from J119 pin 4 in A1 to the pins of the ribbon cable and connector P251 pins 15, 16: Perfect connection.

BUT probing from the plug on the board at J251 pins 15 and 16, to C2010, Voila!

One is open and the other about 1.8K and unstable.

So the open is on board A5!

 Perhaps a bad solder joint or a leaky SMD tant has affected the trace.

Next step is to connect the 2 points (will use a R sub box!)

Jon
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on February 02, 2017, 06:21:31 pm
Hello again Mark! Well something is up:

Connecting a 1K...50 Ohm between J119 pin 4 and C2010 +

a, I can pullup to 9.99V as resistance lowers.

b. there is a huge effect on intensity and stability, it DOES seem to fix it!

c. BUT if I remove the jumper, the scope seems to  no longer shows the fading and instability symptom!

You see the traces,  just at a lower intensity with the 8.85V ref, but it is not fading out every few seconds.  So we are VERY close.

The resistance between the 2 points is a stable 1.275 ohms.

If I probe at J251, pins 15, 16, one is open and at the other pin I get the same R to C2010.

Time to pull out the board?

Best,

Jon
Title: Re: TEK 2467B Odd failure
Post by: tautech on February 02, 2017, 06:25:58 pm
Hello Mark: Indeed the refs at 14 and 15 of U2101 are unstable, fluctuating ~ 0.124....0.136V.

The Refs are also fluctuating, the  +1.36V on J511 pin 24, and -1.25V on J511 pin 15.

Finally there is a 10V REF  bus nearby U2101, bypassed by SMD tant, C2010.



Q+WOW! VERY unstable ~ 7.5..8.15V with dips much lower!

The plot thickens. Perhaps a failing SMD tant, overloading this critical reference? How to distinguish a problem in the 10V ref loads and bypasses vs at the 10V Ref power ckt?

Cheers,

Jon
A known failure mode of Tantalum caps is internal shorts that self heal and they can be a nightmare to diagnose.
Some small mention of it here:
https://en.wikipedia.org/wiki/Tantalum_capacitor#Failure_modes_and_self-healing_mechanism

Google 'tantalum cap failure modes' for more.
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on February 02, 2017, 06:33:19 pm
VOILA! Mark, 

Looking very carefully , I see that there is corrosion around C2520 -15V bypass 0.1 mf and it is JUST near a round can SMD tant, C2113 15 MF SMD -15V bypass

I now think the C2113 is failing, partially, the leakage creept out towards C2520, and has eroded the +10V ref trace!

I needed very bright light and an optiovisor to spot this!

Perhaps a trace for the 10V ref is running under C2520 on the top layer!


(I am very familiar with the tant failures especially on these TEK with SMD tants. )

Time to pull A5 and recap, I think!

FINALLY the end is in sight!

Enjoy,


Jon

Title: Re: TEK 2467B Odd failure
Post by: MarkL on February 02, 2017, 06:48:43 pm
VOILA! Mark, 

Looking very carefully , I see that there is corrosion around C2520 -15V bypass 0.1 mf and it is JUST near a round can SMD tant, C2113 15 MF SMD -15V bypass

I now think the C2113 is failing, partially, the leakage creept out towards C2520, and has eroded the +10V ref trace!

I needed very bright light and an optiovisor to spot this!

Perhaps a trace for the 10V ref is running under C2520 on the top layer!


(I am very familiar with the tant failures especially on these TEK with SMD tants. )

Time to pull A5 and recap, I think!

FINALLY the end is in sight!

Enjoy,


Jon
Excellent!  Sounds like you got it!

Definitely time to recap if you're planning on hanging onto this unit.  But I would fix the trace and replace that one leaky one first to verify it's fixed before starting the recap operation.

Have fun and let us know the final outcome!
Title: Re: TEK 2467B Odd failure
Post by: MarkL on February 02, 2017, 06:53:33 pm
I had already typed up an answer to your question just before you discovered the discrepancy between the two +10V points.

Obviously informational at this point...

...
How to distinguish a problem in the 10V ref loads and bypasses vs at the 10V Ref power ckt?
...

The usual method is to isloate (unplug) the power supply outputs, put them under load, and measure them.  For this unit it's described in the "Regulator Troubleshooting Procedure" (pdf page 474).  Since you only care about the +10V ref, you might be able to get away without loading the other outputs.

The +10V ref is driven by an LM324 (see schematic #10), so it doesn't supply much current and is short circuit protected (max current is 60mA).  One thing you could try is to connect an external power supply to the +10V reference as-is, set the current limit to say 100mA, and try to supply the reference yourself.  This isn't 100% though, since you might end up masking the problem or fighting with an issue in the output stage of the LM324.

If it turns out not to be the supply, finding an intermittent short in a bunch of parallel connected components can be difficult.  It involves isolating branches of the suspect circuit.  For the first foray, this would be disconnecting the various connectors where the +10V ref flows to at least get it down to the board.

Another approach is to use one of these PCB current probes:

  http://www.aimtti.com/product-category/current-probes/aim-i-prober-520 (http://www.aimtti.com/product-category/current-probes/aim-i-prober-520)

It's an investment if you want to expand your collection.  Another option is the old HP 547A current tracer probe.

Thermal cameras can sometimes find a short, but in this case we're talking about a small amount of power which wouldn't generate much heat.

Then there's always the shotgun approach of starting with the most likely failures (like those tantalums you mentioned), and start removing them until you find it.  More drastic measures can also include cutting traces and lifting component legs.
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on February 02, 2017, 08:07:34 pm
Hello MarkL: I now think the 10V ref fluctuations (it was dipping to a few V at times) were causing all the symptoms including the 50 Ohm overload fault. With the jumper in place it works 100%!

What is your thought?

PIX: In these macro photos, we see  the leaky  tant looks OK,C2113  but you can see the leakage at the adjacent 0.1 MF  C2520.

I should replace ALL the SMD lytics!  I wonder if anyone has the best DK or Mouser part numbers to recap A5 in this 2467B?

Again many thanks for all your great assistance!

Enjoy!


Jon

PS: You are Engineer? Ham? Tech? In US or overseas?
 




Title: Re: TEK 2467B Odd failure
Post by: MarkL on February 02, 2017, 09:12:04 pm
Hello MarkL: I now think the 10V ref fluctuations (it was dipping to a few V at times) were causing all the symptoms including the 50 Ohm overload fault. With the jumper in place it works 100%!

What is your thought?
Great!  Can't argue with something that's working now.

I suppose you should do the recap since you already have PCB damage.  Perhaps someone lurking on this thread can chime in with a Digikey/Mouser/etc. parts list.  There's also this thread:

  https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/ (https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/)

which has attracted a myriad of topics on the 246x series.  You could ask over there for a recap parts if no response here, or try the forum's search page.

If you read the thread you will also learn that the Dallas NVRAM in these scopes are at or beyond their EOL.  There's instructions there on reading out its contents and replacing that as well.

Quote
PS: You are Engineer? Ham? Tech? In US or overseas?
An engineer in the US.  I mostly do embedded HW and SW design which doesn't really intersect much with these old scopes.  I have a 2465 and I just enjoy working on them because they're so well documented and repairable.
Title: Re: TEK 2467B Odd failure
Post by: james_s on February 02, 2017, 09:45:32 pm
Those SMD electrolytics are awful, I don't even know why they're as bad as they are but I've replaced thousands of them, usually tantalum or ceramic chip capacitors work well. It was a big problem in older camcorders back when those were worth fixing, and I've repaired a lot of vintage Mac computers that used piles of them. The electrolyte that leaks out is corrosive and damages the board if it isn't caught, as well as it's conductive so it causes malfunctions so it needs to be cleaned off. It causes a chemical change in solder it gets on and seems to raise the melting point. I find the easiest way to replace the caps is usually snip them as close to the base as you can get with a pair of diagonal cutters (watch for flying parts!) and then pick off the remains and remove the pins one at a time with a soldering iron.
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on February 03, 2017, 12:13:29 pm

Hello Mark and James:

In general the 2465B/2467B are the ones worth keeping, the earlier versions are not nearly as desirable.
They are real workhorses and the LAST "real" analog CRT scopes from Tektronix.
The 2467B with microchannel plate intensifier can display very low rep rate or one shot fast transients. But the CRT area is a bit smaller than 2465B.

Having worked with 2465X since 1990s, I am well aware of the infamous SMD lytic leakage and Dallas NV RAM issues.
Of several here, just one has the NV RAM failure and this unit is the first I have seen affected by cap leakage.
It is only with this particular unit, that I have seen the very tiny corroded SMD cap pads, and small visible leakage.
Since most lytics have a 2000 hr life at rated  ripple current and temp, its possible they begin to fail in very high hours units.
Indeed this one shows 1000 starts and 18K hours! The recapping on A5 is easy, on PSU and other boards, its more involved.
Yes the cap replacements are on the other forums. To James, points well taken, I have the Metcal soldering iron (I designed it in 1990s!) for really good SMD work.

For NVRAM, the drill seems to be desolder the old one, add a  socket, and program a new chip. Or do a complete recalibration. Beyond my level of work, but I may find a friend who can do it.

I will post a final note after its finished.

Again many thanks for the very fine troubleshooting from Mark!

Cheers,

Jon
Title: Re: TEK 2467B Odd failure
Post by: MarkL on February 03, 2017, 03:32:29 pm
You're most welcome!  Fun for me too since there's always something to learn.  Good luck on the recap!
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on February 04, 2017, 02:07:01 pm
Hello again: Anyone had experience with QService Greece lately for TEK parts?

Need the Dallas NV RAM and an odd knob shaft etc.
377-0512-03 INSERT,KNOB


156-2991-00 Dallas NV RAM DS-1225Y-200 64K Programmable NV-SRAM


They seem to have no stock on the NV RAM: Looking for one programmed....and with a fresh not 20yrs old date code!

Any tips?


Cheers,

Jon

Title: Re: TEK 2467B Odd failure
Post by: cheeseit on February 04, 2017, 02:42:22 pm
I'm sure someone in the US can help you with the NVRAM but I've used QService a few times and would definitely do so again. They/he provided excellent and helpful service and replied very quickly every time.
Ordered one screw less than I needed last time and when I asked if I could somehow order and pay for one more and have him include it in the first order so I didn't have to pay shipping for a single screw he replied that no order was necessary and he would give me one more. Only a €2-3 screw but still really nice of him. Only problem is that parcel T&T ends when it leaves Greece but he makes a note of this.
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on February 04, 2017, 03:10:59 pm
Actually, the NVRAMS are avail in USA BUT very old date codes and unprogrammed. Seems that QService used to provide them preprogrammed at extra cost.

About the knob insert, its not the insert, the the Intensity 5K pot whouse extra long shaft is bent, that I need, it is

311-2313-01 Potentiometer 5K


With intl post, etc I prefer to find a USA source.

Anyone have a cache of parts or a 2465B/2467B junker or parts unit?


Cheers,

Jon
Title: Re: TEK 2467B Odd failure
Post by: tautech on February 04, 2017, 05:33:01 pm
Hello again: Anyone had experience with QService Greece lately for TEK parts?

Need the Dallas NV RAM and an odd knob shaft etc.
377-0512-03 INSERT,KNOB


156-2991-00 Dallas NV RAM DS-1225Y-200 64K Programmable NV-SRAM


They seem to have no stock on the NV RAM: Looking for one programmed....and with a fresh not 20yrs old date code!

Any tips?


Cheers,

Jon
There's mention of them available from Digikey in this post:
https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg1026013/#msg1026013 (https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg1026013/#msg1026013)
Title: Re: TEK 2467B Odd failure
Post by: james_s on February 04, 2017, 06:59:47 pm
Just cut the old battery out and replace it with a standard CR2032 holder. Then you won't have to source a whole new chip ever again. The battery is on the top under a thin layer of epoxy.
Title: Re: TEK 2467B Odd failure
Post by: FlyingHacker on February 04, 2017, 07:31:37 pm
I believe the unit specific calibration constants are stored in each chip. So you really need to read the old values and copy them, or do a full recal.

I like this idea of replacing the battery with an external one. Got any pics/videos of this?
Title: Re: TEK 2467B Odd failure
Post by: james_s on February 04, 2017, 07:53:46 pm
I don't remember where I originally saw it, on a forum for older Sun workstations I think. I've done it on the NVRAM chip they use since there is a peculiarity that prevents the supposedly equivalent modern replacements from working. If you put the chip in a vice and file into the top you will find the battery, but read the contents out first since removing the battery will cause them to be lost.

Youtube to the rescue:

https://www.youtube.com/watch?v=VV2GHgwrbGU (https://www.youtube.com/watch?v=VV2GHgwrbGU)

https://www.youtube.com/watch?v=NdlSfqto_0o (https://www.youtube.com/watch?v=NdlSfqto_0o)

https://www.youtube.com/watch?v=dqdIfFVXw3c (https://www.youtube.com/watch?v=dqdIfFVXw3c)

https://www.youtube.com/watch?v=2t-hVz8l2e0 (https://www.youtube.com/watch?v=2t-hVz8l2e0)
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on February 06, 2017, 01:15:39 pm
Hello all:

Looking deeper on A5 I found other corrosion damage near the SMD electrolytics, and 3 SMD tantalum caps known to fail

Here is a good link on Groups.io about recapping the PSU and A5 with part nos:
https://groups.io/g/TekScopes/topic/2465b_power_supply_sprague/974763?p=Created,,,20,1,20,0::RecentPostDate%2FSticky,,,20,2,900,974763 (https://groups.io/g/TekScopes/topic/2465b_power_supply_sprague/974763?p=Created,,,20,1,20,0::RecentPostDate%2FSticky,,,20,2,900,974763)

scroll to Tothwolf 10/15/15   #121345    On Thu, 15 Oct 2015, vdonisa

1/ It seems A5 underwent several revs and versions of mod, the SN is critical to locate the coprrect doc.

2/ Lytics are 5mm dia and bypass +/-15 and +5, alsong with nearby 100 nF monothlyics.

3/ As A5 has ADC, DAC and demux for FP controls, corrosion on the board can produce very odd symptoms.

4/ A5 is the ONLY SMD board, all others are thru hole.

5/ Replaceing the Dallas NV RAM: Maxim took over Dallas Semi,  and its on DigiKey.
http://datasheets.maximintegrated.com/en/ds/DS1225Y.pdf (http://datasheets.maximintegrated.com/en/ds/DS1225Y.pdf)
As a 28 pin DIP its easy to swap, especially if you add a socket.

My BIG issue: I have NO programmers for NVRAM, and recalibration is a huge deal. Anyone out there have the capability to read and program the NV RAM?

 As I have several with these same NVRAMS, any help is appreciated.

Cheers,

Jon



 

Title: Re: TEK 2467B Odd failure
Post by: jonpaul on February 06, 2017, 07:47:59 pm
WOW! What a great link and work!

http://www.worldphaco.com/uploads/TEKTRONIX_2465b_OSCILLOSCOPE_CALIBRATION___REPOWERING_THE_DS1225.pdf (http://www.worldphaco.com/uploads/TEKTRONIX_2465b_OSCILLOSCOPE_CALIBRATION___REPOWERING_THE_DS1225.pdf)

Enjoy,


Jon
Title: Re: TEK 2467B Odd failure
Post by: james_s on February 06, 2017, 08:26:24 pm
The programmer is not a big deal, I have a TL866 that handles all this sort of stuff, they're cheap enough that it's worth having one around for that odd time you might need to program or dump a memory IC. As an added bonus it will program lots of different PIC and AVR micrcontrollers, and odd stuff like GALs.

http://www.ebay.com/itm/High-Speed-TL866CS-Programmer-USB-EPROM-EEPROM-FLASH-BIOS-AVR-AL-PIC-/191816776888? (http://www.ebay.com/itm/High-Speed-TL866CS-Programmer-USB-EPROM-EEPROM-FLASH-BIOS-AVR-AL-PIC-/191816776888?)
Title: Re: TEK 2467B Odd failure
Post by: jonpaul on April 19, 2017, 08:41:36 pm
Hello all: Just getting to order the programmer. All the TL866 on epay seems the same, and from China:

"High-Speed-TL866CS-Programmer-USB-EPROM-EEPROM"

Anyone have experience with these? Instruction/software in English? Pitfalls to use on the Dallas DS1225?

Any tips are appreciated,


Cheers,

Jon

Title: Re: TEK 2467B Odd failure
Post by: mtdoc on April 19, 2017, 09:17:52 pm
Hello all: Just getting to order the programmer. All the TL866 on epay seems the same, and from China:

"High-Speed-TL866CS-Programmer-USB-EPROM-EEPROM"

Anyone have experience with these? Instruction/software in English? Pitfalls to use on the Dallas DS1225?

Any tips are appreciated,


See this thread (https://www.eevblog.com/forum/blog/eevblog-411-minipro-tl866-universal-programmer-review/)
Title: Re: TEK 2467B Odd failure
Post by: Satbeginner on April 20, 2017, 11:04:02 am
Hello again: Anyone had experience with QService Greece lately for TEK parts?

Need the Dallas NV RAM and an odd knob shaft etc.
377-0512-03 INSERT,KNOB


156-2991-00 Dallas NV RAM DS-1225Y-200 64K Programmable NV-SRAM


They seem to have no stock on the NV RAM: Looking for one programmed....and with a fresh not 20yrs old date code!

Any tips?


Cheers,

Jon

I recently bought a replacement Dallas at Mouser, and I got one with a 1614 timestamp.
But, this is the newer kind with the battery disconnected till the first use, so I should be OK for the next 10-25 years... :-)

Un saludo,

Satbeginner (Leo)
Title: Re: TEK 2467B Odd failure
Post by: Satbeginner on April 20, 2017, 11:09:35 am
Hello all: Just getting to order the programmer. All the TL866 on epay seems the same, and from China:

"High-Speed-TL866CS-Programmer-USB-EPROM-EEPROM"

Anyone have experience with these? Instruction/software in English? Pitfalls to use on the Dallas DS1225?

Any tips are appreciated,


Cheers,

Jon

Hi,

I just finished a repair and general overhaul of a 2465B, and used the TL866 to read/write the Dallas.

Read here: https://www.eevblog.com/forum/repair/2465b-tektronix-repair-missing-a5-smd-version-board/ (https://www.eevblog.com/forum/repair/2465b-tektronix-repair-missing-a5-smd-version-board/)

I found one little thing: choose the right type of Dallas in the MiniPro program! not the "DS1225 TEST", but the "DS1225 R/W"
Any action with the first chiptype will erase your existing chip loosing the calibration... (happened to me..  :--, but, I had to calibrate anyway, because my A5 came from another 2465B )

Succes!!

Satbeginner (Leo)