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Tektronix TDS540 - Burnt Resistor on DRAM Processor BD

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smbroom
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Joined: August 12th, 2018, 3:32 am
Country: United States

Tektronix TDS540 - Burnt Resistor on DRAM Processor BD

Post by smbroom » August 12th, 2018, 4:07 am

Hello,
Brand new to the Forum and would appreciate any help with my scope issue.
I recently purchased a Tektronix TDS540 Oscilloscope and I am aware of the electrolytic capacitor issues with this series. I have the capacitors in hand but have not replaced them yet. I have not powered the unit on yet because I wanted to perform a visual inspection of the boards for capacitor leakage / corrosion, etc. first. It seems to be fairly clean but will check and clean as necessary.

I found a burnt surface mount resistor on the DRAM Processor / Display board. It's difficult to read the reference # but I am fairly confident that it is “R1037”.
I have enclosed - of its location on the board. It is in the front part of the board near U171, U172, C62, C1225

I do have the Service Manual but no schematic and have not performed any troubleshooting at this time other than a visual check.

I would like to replace this resistor, repair the burnt board and replace the electrolytic capacitors, clean board before powering up the unit.
I would think this is a multi layer board and hope other traces are not damaged.

Is it possible to get the schematic or a least the value of this resistor. I have checked it and it is open. It would be awesome to get the schematic so I can verify the traces on the board for connectivity.

DRAM Processor / Display Board - G92-0658-02 (Label # 671-1477-01)

- included in this post

Thanks for the help, Scott
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strick
Posts: 110
Joined: March 22nd, 2016, 11:23 am
Country: United States

Re: Tektronix TDS540 - Burnt Resistor on DRAM Processor BD

Post by strick » August 15th, 2018, 7:49 am

smbroom,
It is R1037 and it's a 10K pull down resistor for dip switch S1001. This would prevent switch #4 on S1001 from working properly. Anyway, there are procedures in the forum (look for CAP and board cleaning). Use static precautions, Simple Green and a tooth brush to remove the electrolyte that has leaked from the surface mount caps (SMCs). He also gives instructions on removing the SMCs (use a needle nose pliers - push down and rotate back and forth until it comes free). You may pull off some pads on the board and have to use small wires to replace.

The schematic is found on KO4BB website under TDS520

If you have problems when you start, send me a PM and I'll give you specific directions.

Oh, and make sure you do the same to the acq board on the bottom - it's usually in worse shape.

DO NOT TURN THE SCOPE ON until you are finished cleaning and recapping - I use low ESR 35 volt 35 mfd electrolytics everywhere (cost .10 each)
good luck.

STrick

smbroom
Posts: 5
Joined: August 12th, 2018, 3:32 am
Country: United States

Re: Tektronix TDS540 - Burnt Resistor on DRAM Processor BD

Post by smbroom » August 17th, 2018, 3:21 am

Thanks
Last edited by smbroom on August 18th, 2018, 7:57 am, edited 1 time in total.

smbroom
Posts: 5
Joined: August 12th, 2018, 3:32 am
Country: United States

Re: Tektronix TDS540 - Burnt Resistor on DRAM Processor BD

Post by smbroom » August 18th, 2018, 7:56 am

strick wrote:
August 15th, 2018, 7:49 am
smbroom,
It is R1037 and it's a 10K pull down resistor for dip switch S1001. This would prevent switch #4 on S1001 from working properly. Anyway, there are procedures in the forum (look for CAP and board cleaning). Use static precautions, Simple Green and a tooth brush to remove the electrolyte that has leaked from the surface mount caps (SMCs). He also gives instructions on removing the SMCs (use a needle nose pliers - push down and rotate back and forth until it comes free). You may pull off some pads on the board and have to use small wires to replace.

The schematic is found on KO4BB website under TDS520

If you have problems when you start, send me a PM and I'll give you specific directions.

Oh, and make sure you do the same to the acq board on the bottom - it's usually in worse shape.

DO NOT TURN THE SCOPE ON until you are finished cleaning and recapping - I use low ESR 35 volt 35 mfd electrolytics everywhere (cost .10 each)
good luck.

STrick
AWESOME! Thanks for the help. I was aware of the cleaning and the capacitors but was holding off replacing them or powering up the unit until I get the resistor and board issue resolved.

You answered my question on the resistor. My other major concern is how the board is damaged under the resistor. I'm pretty sure that there are internal traces damaged and would be nearly impossible to trace out without a schematic.

As for the schematic, are you saying the TDS520 and TDS540 boards are the same or similiar?
I was able to find a TDS520B manual but wasn't sure if that was what you were referring to.

Thanks for the help!!!
Scott

strick
Posts: 110
Joined: March 22nd, 2016, 11:23 am
Country: United States

Re: Tektronix TDS540 - Burnt Resistor on DRAM Processor BD

Post by strick » August 18th, 2018, 6:10 pm

Smbroom,
the CPU board for the 540 and 520 are exactly the same. The only differences are that the acquisition boards are quite different and the the flash memory has a different firmware. You can switch out 540 with 520 or eve 640 CPU if you reflash the memory. Have to do it with a Debug serial port or GPIB. Later scopes like the 520B/540B had the exact same flash and modified the jumpers on the ACQ board.

Looks like the TDS520 manual was removed from KO4BB. It was scanned by ARTEK Media - you can google that and get the manuals from them if you want. Just search for 520 under the Tektronix label. Cost is about $25 bucks. Way too big to email. I downloaded it a long time ago, but found it useful and paid for real copy. Against the rules to post it.

Anyhow, if the cpu board does not respond with the simple replacement of the resistor, you may have a host of other problems that are unbelievably difficult to fix. Why, TEK had a bunch of routines that they ran on the CPU section in the repair manual that (as far as I know) no one else ever had. That is, they tell you to run a diagnostic and it's not in the scope firmware or rom, so it must have be generated from an external GPIB or Debug port command.

The acquisition board is quite different - everything is self contained and the chips just get timing directions from the CPU. So, once the CPU board is working, you can find the acquisition board problems using the schematics and troubleshooting guide if you look hard enough.

So, if it were me, I would clean the boards, replace the caps and see what happens. If you are going to go much further, you need the manuals, another scope to see signals and all kinds of other stuff. That, and the scope is only worth about 220 bucks, even when it's working...

anyhow, more questions, please send me a PM (if you are able).

:) Good luck
Strick

smbroom
Posts: 5
Joined: August 12th, 2018, 3:32 am
Country: United States

Re: Tektronix TDS540 - Burnt Resistor on DRAM Processor BD

Post by smbroom » August 19th, 2018, 6:01 am

strick wrote:
August 18th, 2018, 6:10 pm
Smbroom,
the CPU board for the 540 and 520 are exactly the same. The only differences are that the acquisition boards are quite different and the the flash memory has a different firmware. You can switch out 540 with 520 or eve 640 CPU if you reflash the memory. Have to do it with a Debug serial port or GPIB. Later scopes like the 520B/540B had the exact same flash and modified the jumpers on the ACQ board.

Looks like the TDS520 manual was removed from KO4BB. It was scanned by ARTEK Media - you can google that and get the manuals from them if you want. Just search for 520 under the Tektronix label. Cost is about $25 bucks. Way too big to email. I downloaded it a long time ago, but found it useful and paid for real copy. Against the rules to post it.

Anyhow, if the cpu board does not respond with the simple replacement of the resistor, you may have a host of other problems that are unbelievably difficult to fix. Why, TEK had a bunch of routines that they ran on the CPU section in the repair manual that (as far as I know) no one else ever had. That is, they tell you to run a diagnostic and it's not in the scope firmware or rom, so it must have be generated from an external GPIB or Debug port command.

The acquisition board is quite different - everything is self contained and the chips just get timing directions from the CPU. So, once the CPU board is working, you can find the acquisition board problems using the schematics and troubleshooting guide if you look hard enough.

So, if it were me, I would clean the boards, replace the caps and see what happens. If you are going to go much further, you need the manuals, another scope to see signals and all kinds of other stuff. That, and the scope is only worth about 220 bucks, even when it's working...

anyhow, more questions, please send me a PM (if you are able).

:) Good luck
Strick
Thanks for the help and great information. I looked at the board, removed the burnt resistor and the board is damaged almost all the way through to the other side. With some very light scratching on the burnt area, I can see down to other layers where the internal traces are damaged. Such a shame. I'm not sure that this area can be repaired. I may see about - up another one and see if I can get one good one from the two.
Thanks again for the help and information. Scott

strick
Posts: 110
Joined: March 22nd, 2016, 11:23 am
Country: United States

Re: Tektronix TDS540 - Burnt Resistor on DRAM Processor BD

Post by strick » August 19th, 2018, 7:32 am

Concur with your choice. Before I would even suggest paying for another 540 CPU board, I would closely inspect the ACQ board. The solder on all the surface mounted parts should be real shiny. If they are not and they are dull, then you've had leaking SMCs for a long time and you can count on numerous breaks between the pads and traces. You also need to look at the front panel as it has SMCs also.

I have fixed no less than 10 acq boards and the 540/640s are the worst. It gets better with the 540A and so forth. By the time TEK started making the 740 series and all "B" and up, they stopped using the SMCs on the ACQ boards and soon thereafter even on the CPU boards.

I have one 640 that I repaired that has 10 wires or other fixes (plus many chip replacements). I keep it as a signal reference as there are no schematics for the ACQ board on this series. It took 50-60 hours of work to get it functioning again and I know some circuits (like triggering) like the back of my hand.
Since I'm doing this as a hobby, it doesn't matter, but otherwise, a real time waster.

Sorry to be so pessimistic, but I don't even look at non-"A" 540s anymore, unless they already pass self-test and SPC.
Strick

smbroom
Posts: 5
Joined: August 12th, 2018, 3:32 am
Country: United States

Re: Tektronix TDS540 - Burnt Resistor on DRAM Processor BD

Post by smbroom » August 20th, 2018, 3:03 am

strick wrote:
August 19th, 2018, 7:32 am
Concur with your choice. Before I would even suggest paying for another 540 CPU board, I would closely inspect the ACQ board. The solder on all the surface mounted parts should be real shiny. If they are not and they are dull, then you've had leaking SMCs for a long time and you can count on numerous breaks between the pads and traces. You also need to look at the front panel as it has SMCs also.

I have fixed no less than 10 acq boards and the 540/640s are the worst. It gets better with the 540A and so forth. By the time TEK started making the 740 series and all "B" and up, they stopped using the SMCs on the ACQ boards and soon thereafter even on the CPU boards.

I have one 640 that I repaired that has 10 wires or other fixes (plus many chip replacements). I keep it as a signal reference as there are no schematics for the ACQ board on this series. It took 50-60 hours of work to get it functioning again and I know some circuits (like triggering) like the back of my hand.
Since I'm doing this as a hobby, it doesn't matter, but otherwise, a real time waster.

Sorry to be so pessimistic, but I don't even look at non-"A" 540s anymore, unless they already pass self-test and SPC.
Strick
I understand. I don't mind a good challenge every now and then and have done electronic work for about 40 years. I have never seen anything like this...in this scale. Again, many thanks for the help!

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