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]

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.

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!

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.

[Tantratron]

Well, there you go.... I just checked the three spare PSU's I have here, and they are all different!

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..

Many thanks Terra for taking time to report, pictures and comment.

In the meantime, I've looked at my older notes since 2019 where progressively, I've had in hand 9 different models. Just made bit clearer notes, see attached my new hand writing normally I did not make a visual copy mistake.

In RED is old PSU design which I've found in one TDS510A and in one failed TDS784D, the later is a complex topic with this old PSU failed, logic board failed, color CRT damaged physically.

On the old PSU, there are 3 PCBs (main, vertical 1 and vertical 2) but with my two units, no part number neither version letter as printed with new PSU design (only two PCB's).

Not sure what I can do with the two old PSU, one still works but I understand the need to upgrade C17 and RIFA's as you mentioned. The 2nd will not start, only standby click then stop then click then stop.

Do you think best to only keep new PSU design for all models (A, B, C and D) due to better design ?

As for your last PSU with +25Vdc/4A for sure it is not due to Artesyn purchasing Zythech as my document shows clear evidence with dates, part numbers. Could you check on this unit what are the RLB and TLB part number and revision letter to see if it corresponds to my list ?

Maybe they printed a wrong marker because 400W 4.5A grid part as previous model whereas I'd expect say 450W due to higher power from +25Vdc rail.

[Tantratron]

P.S. This could be a cross refernce thread but seems very important preventive repair for those willing to keep working old PSU design https://www.eevblog.com/forum/repair/tektronix-tds744a-cannot-boot-completely-flashrom-checksum/msg5166528/#msg5166528

[inlinebeginner]

P.S. This could be a cross refernce thread but seems very important preventive repair for those willing to keep working old PSU design https://www.eevblog.com/forum/repair/tektronix-tds744a-cannot-boot-completely-flashrom-checksum/msg5166528/#msg5166528

Tantratron
  I saw your question in above link about replacing C17 or finding a new PSU, it better to move our discussion to this topic.
  My suggestion is: replace C17 first, then replace C93,C94 and C102 (10u/35V).   The PSU design was good, seem to be reliable.
  I repaired four, two TDS744As, one TDS684A and one TDS754C. The TDS 754C PSU, different form TDS744A, does not contain a C17, because its standby circuit was redesigned. After repair, all work well.

Lin

[Tantratron]

  My suggestion is: replace C17 first, then replace C93,C94 and C102 (10u/35V).   The PSU design was good, seem to be reliable.
  I repaired four, two TDS744As, one TDS684A and one TDS754C (PSU is different form TDS744A, the C17 was removed in TDS754C PSU). After repair, all work well.

Hello Lin, it seems almost certain due to year of production that all TDS744A make use of old PSU design.

Your sentence which I quote again one TDS754C (PSU is different form TDS744A, the C17 was removed in TDS754C PSU) is not clear. Do you confirm this TDS754C-PSU is new design, if yes where is C17 ?

Have you ever seen any TDSxxxC/D using an old design PSU or were there all new PSU design ?

On a side note, I have only repaired so far one TDS794D-PSU few years ago, it consisted to replace to power mosfet transistor Q7 and Q8 switching the +400 Vdc rail to the down-converter trafo.

[inlinebeginner]

  My suggestion is: replace C17 first, then replace C93,C94 and C102 (10u/35V).   The PSU design was good, seem to be reliable.
  I repaired four, two TDS744As, one TDS684A and one TDS754C (PSU is different form TDS744A, the C17 was removed in TDS754C PSU). After repair, all work well.

Hello Lin, it seems almost certain due to year of production that all TDS744A make use of old PSU design.

Your sentence which I quote again one TDS754C (PSU is different form TDS744A, the C17 was removed in TDS754C PSU) is not clear. Do you confirm this TDS754C-PSU is new design, if yes where is C17 ?

Have you ever seen any TDSxxxC/D using an old design PSU or were there all new PSU design ?

On a side note, I have only repaired so far one TDS794D-PSU few years ago, it consisted to replace to power mosfet transistor Q7 and Q8 switching the +400 Vdc rail to the down-converter trafo.

Hello Tantratron, Sorry for the confusing, I edited my statement: "The TDS754C PSU, different form TDS744A, does not contain a C17, because its standby circuit was redesigned."
"Have you ever seen any TDSxxxC/D using an old design PSU or were there all new PSU design ?" I only repair one, TDS754C, its PSU might be a new design around the standby circuit, that is why it does not contain a C17.


Lin

[Tantratron]

Thanks @inlinebeginner for clarifying the C17 topic where as a reference, my very first post shows pictures of old and new PSU
https://www.eevblog.com/forum/repair/tektronix-tds500-tds700-power-supply-models-psu-repair/msg5160828/#msg5160828

Yes clearly the standby circuit seems really different, same for the PFC-boost converter section when dealing with new design. As you know, there are no schematics for TDSxxxC/D but the low volatge DC output parts seem similar. The differences are really the standby section and the PFC-boost section plus I find new design easier to access the mosfet, the screws...

[TerrySt]

Terra,
Thanks for the heads up on the capacitors in the old power supply that need changed.  I have my old 524A opened up to work on the CRT power supply, so I'm going to change the parts you suggest (C17 and the 4 RIFA caps).
I noticed that in the picture you posted of the old supply with the suspect parts circled, that you circled C16 instead of C17.  C17 is the cap right next to the one you circled.  At least that's how it looks on my supply, which matches your picture.  Unfortunately I don't have a parts diagram for that model of supply to be sure, but the part next to the one you circled is 47uF at 80V.

Terry

[TERRA Operative]

Ah, I may have made a mistake. I'll correct the image and reupload it tonight.

[TERRA Operative]

Corrected image is now uploaded.

[Tantratron]

Hello Terra, it took a while to import from eBay-USA to France but finally got your amazing TDSxxx tester.

Attached pictures showing its use on a valid PSU (new style) then later, I'll try to use it on my two old style PSU, one being broken.

I understand your recommendation to replace some RIFA caps first to not aggravate these two PSU.

Respect for your work, Albert

[TERRA Operative]

Nice!

Let us know how your testing goes!

[Tantratron]

This morning I've connected the PSU tester into the old style PSU which has been failed for mor ethan 3 years and just sitting here. This time, no LED lights up where from what I see or hear, there is some kind of oscillation or attempt to run the standby.

As for the four RIFA capacitors, what new part number do you purchases to be equivalent ?

When the PSU tester does not show any LED to be ON, what other means could I use to investigate the power on failure through the PSU tester ?

[TERRA Operative]

For replacing the Rifa capacitors, I used part number R413F11000000K but any similar equivalent would be fine.

As for troubleshooting, check the parts I pointed out in the image I posted above. If there is no standby voltage, then that part of the circuit is probably bad.

[PwrElectronics]

I hadn't read this thread when it was originally posted.

Don't have any advice on repair of these but....

I was a product and test engineer at Zytec from 1994-1996 and worked in the factory in the small town of Redwood Falls, Minnesota where these were made.  I remember seeing them in an adjacent production line area to the one I was assigned to.

Zytec was a spinoff of Control Data (mainframe computers) power supply division in the 1980s when Control Data was closing down.

Zytec merged with some other company whose name escapes me around '97 or '98 and the joint company was called Artesyn.  This lasted a few years until bought by Emerson and it was known as Emerson Power Systems or Emerson Network Power.  A few years back, the name returned to Artesyn Embedded Power.  Now, its been bought by Advanced Energy in 2019.

The Redwood Falls factory was closed/sold around 2000 or 2001 and production was moved out of the USA.

[DavidAlfa]

Just repaired the PSU from a TDS 520D, found no schematics, it was blowing the breaker.
The PFC circuit has two small bjts driving the big fets, the 2n4401 was shorted so it was setting the fet permanently on.
Replaced with a MPS2222A, it's back to live, 420V generated in the beefy cap.
It's had been touched before (Failure sticker from 2017), the IRF450 fets looked new.
Though the guy gave up and put a sticker "Short in transformer" .

[TERRA Operative]

I had a PSU with a similar failure a while back.
I was lucky enough to find original parts, but if substitutions fits, it sits. 

Nice work!

[DavidAlfa]

It's just a generic 500mA 50V bjt, if it fits, it fits. Nothing fancy required here!