A GW Instek, PSP-405, Lab bench power supply repaired

[matt6ft9]

No help needed on this one, just hoping to help someone else out.

The series of GW Instek, PSP-405 lab bench power supplies has capacitor issues.  We have about ten of these power supplies.  In the past year, three of these power supplies have failed.  They start acting up by the output not turning on consistently.  The next stage of failure is all of the LCD segments turning on when the PS powers up or the PS being completely dead. 

The GW Instek, PSP-405 is a 40V, 5Amp, programmable bench power supply.  The programmable part of the power supply is though a 9-pin RS-232 connector on the back of the supply.  Amazon has the power supply new for $310 USD, which seem really high to me.  The power supply was also found under another brand:  Iso-Tech ISP-405.   (At least, the faceplate and specs look identical)  I’m not sure if any others in GW instek PSP series have the same cap issues.  They are the PSP-603 and the PSP-2010.

Two of the failed power supplies were 9 years old, with the third failure being a 5 year supply.  All of the power supplies had issues with the four capacitors (see "four caps.jpg") 

On the 5 year old power supply, it was showing the first stages of failure with the output not turning on consistently.  There were no blown tops on the four caps in the 5 year old supply.   (but there were vented caps on the previous power supplies) After the 4 caps were removed, here are the ESR readings:

Capacitor   Printed value   Measured Value   Measured ESR   ESR of a Good Cap
C25   470uF, 25V   409uF   4.1 ohms   0.25 ohms
C29   470uF, 25V   414uF   3.9 ohms   0.25 ohms
C33   470uF, 25V   434uF   4.3 ohms   0.25 ohms
C49   100uF, 100V   86uF           21 ohms   0.4 ohms

Digikey has some good replacement caps:
C25, C29, and C33:  Part number P12389-ND, CAP ALUM 470UF 25V 20% RADIAL
C49:  Part number P5313-ND, CAP ALUM 100UF 100V 20% RADIAL

So far, all three power supplies with the new caps are performing well.  Anyway, I hope this helps someone out.

[attie]

Hi matt6ft9,

I just wanted to say thanks very much for posting this!
I've been handed a 'junk' ISO-TECH IPS2010 that I've been hoping to get up and running again.
The power board looks incredibly similar to your photos.
I've had a look for schematics and things before, so your post and my free time were very well coordinated! :-)

I'm going to replace the caps you've mentioned, C25 and C29 are indeed slightly inflated on my board...

I just wanted to check what symptoms you've seen.
This supply will sit, seemingly 'resetting' (brownout?) and clicking (from BZ1 on the logic board), with the LCD flickering in time with the clicks.
If you leave it long enough it does tend to startup properly, but then fails to switch on its output...

Cheers,
Attie

[JoeO]

Attie:

matt6ft9 documents the symptoms he is seeing.  Re-read his post.

Replace the 4 caps that matt6ft9 did since you can see that 2 of them are already defective.  Then trouble shoot from there.

[attie]

Thanks JoeO,

I was hoping for an expansion on the following:

The next stage of failure is all of the LCD segments turning on when the PS powers up or the PS being completely dead. 

For example, is he hearing the clicks too?

I'm planning to replace the caps, and I will indeed trouble shoot from there... I'm not sure what else you thought I was going to do...

[matt6ft9]

Attie, I was not able to find schematics either.  (not too surprising)
The power supplies differed some in the failure.  One of the failed supplies would have a relay click several seconds after power up.  (relay on the power board?)   But, the first symptom was the output not turning on when it should.  If you would hit the output button again, it would come on.  Once it progressed to the state of all of the segments on or none the segments on, there was no coming back no matter how long you left it on.
If you have an ESR meter, you can use it on some of the large electrolytic caps while they are still in circuit.
Here is a table of ESR values you should be reading.
https://www.eevblog.com/forum/beginners/esr-values-for-electrolytic-caps/
Matt

[tautech]

In the absence of an ESR tester, a "trusted" capacitance meter might help.
matt6ft9's values in the OP are 10% or more away from nominal values.
This would send up a big red flag for me.
An ESR test would then be only a confirmation of the culprits.

[attie]

Hi matt6ft9,

I just wanted to post back and say "thank you very much!"
The supply is now up and running again

Attie

[matt6ft9]

Attie,  That's awesome!  Matt

[googolp]

You saved me too matt6ft9.

The first symptoms was the power supply spontaneously turning off under load. After that it began clicking and the LCD was flickering. Eventually it just wouldn't turn on.

After some investigation I found that the MCU was being reset by the 5V power good line. After probing the 15V rail I saw that it was climbing very slowly and eventually when it reached 15V the screen and MCU came back to life (this would sometimes take more than a minute). Moments after connecting a load it would die again and the long wait for the 15V rail would start all over. I discovered would die each time the fan turned on, this explained why it would die under load.

Anyways, I found this post and replaced the caps. The GW Instek PSP-2010 is working again.

Cheers.

[Conseils]

I have used these supplies for around 8 years. When purchased, I had a failed unit after a couple of days. It was super urgent, so I replaced one of the capacitors you identified ( C29 ) with a huge, Radio Spares 63v 470uF 85°C variant. Fully expecting the power supply to retire shortly afterwards. Almost 10 years later it seems to be still going strong! I wonder if the original capacitors are either really poor, under rated or over loaded.

With the idea of perhaps fitting a PiZeo to allow Wifi control, http interface and some data logging; together with a small calibration tweak and remembering the dodgy capacitor issue, I popped the lid off for a peek inside again.
 
Sure enough, all the capacitors you identified have a lovely crusty brown exudation on the top! It still worked seemingly satisfactorily according to my pre calibration check. So maybe my calibration check was bit overkill but what a find, then I came across your lovely post!

By the way, my unit is the Radio Spares RS ISO-TECH IPS-405 which appears to be as far as I can discern identical inside.

Ordered some lovely Panasonic replacement capacitors.

Thanks for posting.

 

[Conseils]

Following from my previous post..

My 'dodgy' capacitors measured 245 and 104 uF. Whilst the previously hacked large 63v RS capacitor measured 498 uF (no issue with that one it seems).  They were of course all supposed to be 470 uF nominal. So the brown crusty stuff must be magic smoke related at least ;-)

Following the repair I measured the heat sink temperature near these capacitors. This was to see if the heat sink was running warmer than might be anticipated, perhaps leading to degradation of the capacitors. As I haven't really run the power supply continuously at full load, to 'stress' the capacitors.

Set at 5.00 volts (5.0012 measured) and with no load, after 30 minutes the heat sink measures 63.9 °C in a 20.1 °C ambient.
The fan mounted in the unit runs very occasionally for a couple of seconds under this no load condition.

I had adjusted the potentiometer SVR1 on the computer PCB to adjust the voltage output at the terminal posts. This allowed me to pull in the power supply output voltage easily by ~15mV to bring the power supply output voltage nicely nearer to the indicated voltage on the units display panel.

You can see the potentiometer that was adjusted on the attached image.

Thanks again for posting.

[matt6ft9]

It’s good to see so many using this post.  ‘just had another one start exhibiting the same problems today.  After opening it up, C25 and C29 had vented and made brown residue on the lid of the enclosure.

I replaced the four caps and the power supply seems functional again. 
Matt

[dgtl]

Another one fixed here. In my case C36, C37 and C19 had too high ESR (their capacitance were ok and no brown spots of venting, bulging or other marks of damage). After replacing these three, the supply is working again.

[c_04]

Hi
I have PSP-603 power supply, mine uses 8951 uC with separate board signed as DPS4005. Is there anyone who could share bin file for this uC. Today ive checked - my is blank. I can share bin file for eprom if needed. My is 27C512 rom is V.1.89. It would be even great to get firmware for example PSP-405 just for tests - if will not work correctly.
Regards
Greg

[Wollvieh]

Just for the records, there is a schematics file out there, find attached.

This one is for the DSP-4005, which is quite similar to the DSP-6003 and DSP-2010 which also come as IPS-2010, IPS-4005 and IPS-6003 from various companies like GW Instek, Voltcraft, ISP, Iso-tech. Just to feed the search engine.

The boards may vary over the years.

[fest]

I obtained a similar model (IPS-603) whose front display and keypads worked just fine, but output stayed at 0V regardless of settings.
After replacing the caps (didn't help) I continued debugging and found out that leads of one of the main switching transistors (Q1) had been trimmed off too short and did not make contact with traces on the bottom layer.

[LogicalDave]

I purchased a PSP-2010 on eBay.  It is in good condition and has a white adhesive securing the electrolytics to the board, so perhaps Instek has moved away from the problematic brown adhesive.  The caps do not appear to have vented.  The only issue is the rotary encoder, which will often move the value being adjusted more than one step and sometimes in the wrong direction.  The encoder looks like a common 3-pin through-hole EC12 rotary encoder like Bourns PEC12R-4220F-N0024 or TT EN12-HN22AF20.  Has anyone had the same issue? Does anyone know the exact replacement part number for the encoder? It is marked with a Chinese character; it seems to follow the EC12 footprint, the shaft is 6mm diameter, 10mm long (tip-to-bushing), 15mm long (tip-to-body), 20mm long (tip to PCB).
Also, any recommendations for cleaning the button contacts? isopropyl alcohol?

Finally, I've included a pic of the front panel board to add to this thread

[LogicalDave]

It turns out that a standard EC12 rotary encoder fixed the problem.  You want one with roughly 24 counts per rotation and ideally 15mm.  The board wants one without a switch, but I used an encoder that has a switch (push the wheel in to close switch); I just bent the switch leads up and connected them to the nearest vias which activate the Enter button...so new functionality :-)

I was in a rush so I ordered encoders from amazon: https://www.amazon.com/gp/product/B0838S2LR1/
These have a 14.3mm shaft instead of the ideal 15mm, but it was no problem and fit perfectly.

I think the exact match is TT part EN12-HS22AF20.  Note that encoder height measurement methodology seems to vary by manufacturer.  The original encoder has a 6mm diameter shaft; the body extends 5mm above the PCB, the bushing adds another 5mm, then the rest of the shaft is 10mm.  TT calls that a 20mm encoder, many others describe this as 15mm.

[jeka1981]

Does anyone know how to convert it from 115V to 230V ?

[nctnico]

According to the manual it can run from both 115V and 230V. It seems to be auto ranging.

[jeka1981]

But in real life it's not like this. It has a switch for 115V and 230V, but for 230V it doesn't have a cable connected for it to work.
I think think that it's a scam with 115V and 230V switch. Isaw only 2 200V capacitors - only for 115V.
It needs to be modded to 230V by myself. So, i need schematick or pictures from a EU 230V version.

[jeka1981]

Here is the picture of it :

[avrusb]

That is perfectly fine. The switch is only closed or open. See this schematic for example:



BTW, PSUs with this kind of switch are not allowed in Europe anymore for new production. With PFC, it is not necessary anymore.

[Paceguy]

From the photos in the original post, I see that the problematic caps were located right beside a big heatsink. Over the years, I have noticed that caps that are subjected to heat fail faster. This is a frequent problem in the Fluke 8840A/8842A DMM's. The two 470UF caps are right beside the pwr. supply regulator heatsinks. These caps are found to be open frequently. It's also a problem in LCD TV's where pwr. supplies generate alot of heat.

[mahmut47]

f2 fuse always blows up and i cant fix it please anyone tell me how to repair my power supply