HP6035A 500V 5A 1kW Power Supply Repair

[Jay_Diddy_B]

Hi group,

I am going to share the steps I took to repair a HP6035A 1kW Power Supply.

Before I get into the details, these power supplies are off-line switching supplies. A large portion of the circuit is connected directly to the line. Read and understand all the warnings in the HP Service Manual before attempting repair of these units.

The nature of this circuit, is that if you don't repair everything, it will fail catastrophically again. It is very important to find all the damaged components.

This power supply can deliver over 1kW for output voltage between 200V and 500V.

Details of this power supply and the service manual can be obtained from the Keysight website:

http://www.keysight.com/en/pd-839427-pn-6035A/system-autoranging-dc-power-supply-500v-5a?cc=US&lc=eng

Problem

When powered up and turned on an error message was displayed indicating a problem with the secondary circuits:



I removed the outer cover by removing the handles on both sides of the power supply. I also removed the inner cover to reveal the inside of the power supply:



Bad Electrolytic Capacitors

Looking around I found some leaky electrolytic capacitors:



Here is another view:



I removed the capacitors to reveal a real mess on the pcb:



I cleaned the area with alcohol (IPA) and small brush. This revealed some damage to tracks under capacitors:




Repair

I replaced the damaged tracks with jumper wires:



Other damage

Changing the capacitors and repairing the damaged tracks did not fix the problem. I was still getting the 'SEC Bad' error.

I looked some more and I found, that R34 on the FET board was burned and open. I replaced this with a 1/4W 2.7 Ohm resistor:



I also found that C18 on the main board was short circuit, so there was no 9V supply.



Working Properly

I put the power supply back together and cleaned all the labels and dirty from the outside of the case:



Regards,

Jay_Diddy_B

[nctnico]

Interesting. Did you consider to replace all the electrolytic capacitors? It is reasonable to expect more will be poor condition.

[Monittosan]

since there are so many large value high voltage caps id expect if these needed to be replace it would be uneconomical to repair

[sync]

Leaking Nichicons again. 

[nctnico]

since there are so many large value high voltage caps id expect if these needed to be replace it would be uneconomical to repair

Capacitors aren't that expensive. I replaced the electrolytics in two HP6024A power supplies and that added up to about 50 euro each. I could have done it 50% cheaper if I didn't use high quality long life low ESR capacitors.

[Jay_Diddy_B]

Hi group,

Here is a photo of the Nichicon PR(M) 1000uF 50V capacitors that I removed. The one the left has been cleaned and I cut part of the plastic sleeve away to reveal the seal:



This problem is certainly not unique to the PR(M) series. Here is a handful of VZ(M) capacitors that I pulled from a Keithley 2001 DMM. Every single capacitor was showing some signs of leakage. I have cleaned the board in the Keithley and will be replacing the capacitors later.




For those who suggested replacing all the capacitors. I would certainly change all the similar radial can electrolytic capacitors that were made by Nichicon. The main input capacitors have completely different sealing technology, these capacitors have screw terminals. On later units these capacitors were replaced with capacitors with a three pin base.

I am also working on a HP6030A (200V 17A) power supply. In this supply one of the capacitors vented through the side of the can. Here is a photograph:



This capacitor is particularly large for its value. It is 1600uF 125V. The can size is 45mm diameter x 80mm tall. I believe that this is a special high-ripple current capacitor. I have ordered replacements from Keysight. They are $30.00 USD each.

Regards,

Jay_Diddy_B

[nctnico]

IMHO the large capacitors are just big because they are old technology. Modern, low ESR capacitors should do just fine and may even be better than the originals! Original replacement capacitors would make me worried about getting old stock (remember electrolytic capacitors have a limited shelve life). OTOH they fit without problems. I've attached some pictures of my HP6024A restoration project.

[Jay_Diddy_B]

Hi Group,
Normally I would agree with nctnico that modern capacitors are smaller and may be even better than the originals.

But in the case of the HP6030A Output capacitors, I think that this is an exception. I think that the capacitors were specially engineered.

Schematic



The Output are C13 and C14. They are connected in series. This is a Flyback supply so each capacitor sees the maximum ripple current when the output current is 17A.


Capacitor Measurement



I put the good capacitor on my HP7274A LCR meter. It has a very low ESR of 17.7m Ohm. This much lower than any capacitors I can find on Digikey.

Power Loss in the capacitor is Iripple² x ESR

Temperature rise is proportional to Power loss and inversely proportional to surface area. The large can has lots of surface area.

I will measure the new capacitor when I get them from Keysight. The power supply is still in production, so I have no reason to expect old stock.


Regards,

Jay_Diddy_B

[nctnico]

Hi Group,
Normally I would agree with nctnico that modern capacitors are smaller and may be even better than the originals.

I put the good capacitor on my HP7274A LCR meter. It has a very low ESR of 17.7m Ohm. This much lower than any capacitors I can find on Digikey.

Are you sure? I can find a whole bunch of capacitors with equal or lower ESR than that at Farnell/Element14. I couldn't find an exact fit though but they should be out there somewhere.

[SeanB]

5W in ESR alone at full power. You need the right capacitor there, as experience in trying to design TV set flyback coupling capacitors taught manufacturers years ago. Same value and voltage but wrong construction and it burns up. That big can is there to handle that 5W of power, even at high ambient, and still have a good operating life.

[vtp]

While you are doing that 6030A check also the input capacitor bank. I removed the capacitors in mine and used 4274A (I have one too!) to measure them. The capacitor electrically closest to higher side FET of the two transistor flyback primary is stressed most.

Eventually I did not want to change those caps because the only source really appears to be Keysight and they were not that far gone: highest ESR was about 36 mohm, lowest around 15 mohm. I just "mirrored" the bank so that in schematics the bottom left cap went to top right and so on. My 6030A is also of newer type where there are only 6 large input caps. IIRC they are not 1600uF but 1800uF.

I also bought my 6030A faulty. It had one gate drive transistor fuse blown. That was the only issue with it. However, due to why, I suspect HP had made a goof in production and the primary side current transformer wire that is soldered on board had too long tail. Eventually it probably touched very briefly the chassis - and it certainly did after I installed the board back in. Maybe it would be worth checking that there are no too long (component) wire tails protruding under the PCB. The chassis is ground and that very low ESR capacitor bank guarantees light and sound effects if parts of the wiring touch chassis.

[Yansi]

5W in ESR alone at full power.

How did you get that? The ripple current throught tha cap is not the same as the output current.

The flyback secondary curent is a ramp function with a zero current phase in between. The capacitor current is the secondary current minus output DC current.  To estimate the secondary effective current, you must know the flyback's duty cycle.

[SeanB]

That is just the output current heating inside, the charge current will of course be higher.  You always have this problem with capacitor selection when you have high current peaks charging, like in TV flyback and a CUK converter. All there burn capacitors if poorly selected.

I would guess the capacitor is handling around 15W at full current, just from assuming that then charge current is 33% duty cycle.

[Yansi]

Read please what I've explained once again. You absolutely cannot make estimations like "output current heating the cap" - thats pure nonsense.

This is what you must integrate for estimating the cap's effective ripple current



And no,won't be anywhere near 15 Watt.

[Jay_Diddy_B]

Hi,

If you are reading this thread, you may be interested in the 3D printed bus bar cover that I shared here:

https://www.eevblog.com/forum/testgear/replacement-knobs-feet-and-fittings-for-test-equipment/msg3274678/#msg3274678

Regards,
Jay_Diddy_B

[Fretec]

Yansi is right, it won't be near 15W. And if it was, the caps would have another fan cooling them.

[Jay_Diddy_B]

Hi group,

Today I replaced all the Rifa Capacitors in an HP6035A. The original capacitors were cracked and looked like they were ready to fail:







There are six Rifa capacitors on the EMC filter assembly:




There is one capacitor on the main board:




This is an after picture, the capacitor has been replaced.

This one looks like it going to require major disassembly to replace. Fortunately, you can replace this part without removing the PCB. You can access the solder joints through a holes in the chassis:





Parts used

HP 6035A - Rifa Capacitors         
         
Input Filter         
         
Description   QTY   MFG Part No.   Digikey
         
CAP FILM 1000PF 20% 1.25KVDC RAD   2   PHE850EA4100MA01R17   399-5415-ND
CAP FILM 2200PF 20% 1.5KVDC RAD   2   B32021A3222M289   495-5035-1-ND
CAP FILM 10000PF 1.25KVDC RAD   2   PHE850EB5100MB04R17   399-5419-ND
         
         
Main Board         
         
CAP FILM 0.047UF 20% 275VAC RAD   1   PHE820MB5470MR17   399-7598-ND

Regards,
Jay_Diddy_B