Electronics > Repair
tektronix TDS500 TDS700 power supply models PSU repair
Tantratron:
Hello, I've been using for my lab as well as trying to repair, recondition or hack different TDSxxx/C/D models plus purchased of pure interest a TDS510A.
Different threads discuss the topic of CRT, the logic board, the acquisition board but I notice two versions for the PSU board (old style and new style). I'm attaching differents pictures of both models where the old design seems to differ only on the EMI filtering, the PFC boost converter and the standby circuitry.
Unless I'm wrong, it seems that old models might be fully compatible or inter-changeable with new models where you would just need to use the appropriate flexible ribbon and connector to match the specific acquisition board power rail ?
What is your return of experience, which model do you think is more reliable with less failures ?
In the past, I did repair one new model by changing two mosfet transistors of the PFC output.
Now I do have a failed old model which seems to have faulty standby issue, it starts then stop then starts...
Do you confirm to have working old PSU installed in your C or D oscilloscope or do you recommend to not spend time repairing old PSU's ?
Similar question, do you confirm new PSU working inside a A or B model ?
Thank you in advance, Albert
TERRA Operative:
The new type PSU can be used in place of the old type PSU no problems. The only real difference in output is the new PSU can supply 4A on the +25V rail whereas the old PSU can only supply 2.5A.
So new can be used in place of old, but I wouldn't use old in place of new without verifying current draw on the +25V rail.
The benefit of the new design is that it doesn't suffer from capacitor C17 going high ESR and taking out the TVS diodes and BU508 transistor, also no Rifa madness, as all those parts simply don't exist.
I have attached your image showing the location of these parts. If the PSU works, the capacitor C17 (47uf, 80V) should be replaced without any hesitation to prevent future damage to the TVS diodes and transistor. It will be bad. Use a good quality LOW! ESR capacitor of equal or greater voltage rating (I personally like the United Chemicon KY* and KZ* series, but any good quality part can be used).
If the PSU does not work, you may need to replace the two TVS diodes VR4 (1.5KE220CA) and VR5 (1.5KE250CA) and transistor Q9 (I use a BU508AW) too, so that's the first place to look after replacing the capacitor.
The most common failure mode is no power when pressing the front power button on the scope. If this is the issue, check these parts first (after checking the line fuse and mains supply..)
An easy check is to listen carefully right when plugging in the mains power cable. If you listen closely, you should hear a faint 'ziiippp!' sound as the standby circuit powers up. This indicates that it is probably working.
As for Rifa caps, there are 4x 1000pf 10mm pitch Rifa caps in the old PSU that should also be replaced on sight.
Tantratron:
--- Quote from: TERRA Operative on November 13, 2023, 01:31:29 am ---The new type PSU can be used in place of the old type PSU no problems. The only real difference in output is the new PSU can supply 4A on the +25V rail whereas the old PSU can only supply 2.5A.
So new can be used in place of old, but I wouldn't use old in place of new without verifying current draw on the +25V rail.
--- End quote ---
Many thanks TERRA for explanation on which cap, diode and transistor are critical in old style PSU.
As for the +25Vdc output rail, not sure of my new PSU being different than the ones you refer to. Please check attached different pictures I've just taken from my three PSUs (two old style, one new) but it seems all source 2.5A output for +25 Vdc.
I do have two other new PSU but they're installed in my test lab (TDS794D and TDS784D each with LCD kit) so I'd need to open all (long time to deconstruct) to check if more recent new shifted to 4A output for +25Vdc rail.
Do you confirm the 4A output, what year it was made since attached time stamp of my new PSU is 1998 as you can see on my last attached picture ?
Tantratron:
Hello again TERRA, I've checked now my old notes to track different part number, versions wether PSU, the CPU board, acquisition board, CRT board based around nine TDS different C/D models.
Are you really sure that newer PSU has specific 4A on +25Vdc rail output because in my notes, I see all these PSU from TDS754D TDS520D TDS784C TDS794D and TDS714L produce 5V/22A -5.1V/12A +5V/12A +15V/1.5A -15V/1.5 and +25V/2.5A
All the AC-grid inputs wether built by ZYTECH and later acquired by ARTESYN mention 400 W/100-250Vac/4.5A different Revision (RE F G or K) all built between 1997 and 1999
Thanks to check again, Albert
TERRA Operative:
Well, there you go.... I just checked the three spare PSU's I have here, and they are all different! :o
The pictures are below, grouped by part number as per the label.
The older one and one of the newer ones I have are both made by Zetec and have exactly the same output specifcations. They have the same Tek part number besides the last two digits (-04 to -05) which indicates a cross compatible upgrade to the higher part number.
The other later one made by Artesyn with 4A on the +25V rail has a completely new Tek part number, so I'm not sure if the one was used for a specific scope model or if it was just how it ended up when the PSU manufacturer changed from Zytek to Artesyn..
Maybe more power was needed for the D suffix TDS700 series scopes? I don't know.... I can't remember where these PSU's were pulled from.
Also, I know that some TDS500 scopes (I.e. TDS520 maybe?) have yet another PSU design, the long black DC output connector that is furthest from the mains input is smaller, so it isn't compatible with scopes that use these PSU's we are talking about. I have a scope that uses one of those PSU's, but it's a pain in the arse to remove for a photo, so.... no photo of that one. :P
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