Delta TDPS-138AF Avaya no output repair

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

My reasoning for this measure is because:
The PSU came back to me the second time with the same failure on the exact same spot.
I did measure all 4 caps out of circuit capacitance and resistance. While the capacitance was bang on through the remaining capacitors, the resistance was not.

One cap was my replacement, 3 where originals which one of them failed. The failed cap had 345 Ohm resistance and no capacitance on the DMM. My replacement cap had rated capacitance, the resistance was like 50 something MegOhms. I almost measured the same on an original cap, so that was good. However the last original cap while it had capacitance same as the others, the resistance was like 3MegOhm. So I figure this is the next one to go. So I just replaced them all 4 caps with new 50V 10uF.

[sam_sam_sam]

Re: Delta TDPS-138AF Avaya no output repair

I was wondering about weather or not a good idea to replace all four of them at the same time is it unusual for this type of capacitor to go bad like that

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

Got the original PSU back. Blown again. Same place same part. One of the 4 chip capacitors in parallel failed.The one I put in is still good. This time I had a 345 Ohm short across the capacitors.

NOW: I recommend to replace all 4 chip caps at the same time!

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

Well that was a easy lucky fix. I haven’t seen your problem on these PSU’s over here, but there must have been quite the voltage spike for the bridge rectifier to go short. Another one kept out of the land fill!

[gsan33]

Re: Delta TDPS-138AF Avaya no output repair

Just successfully repaired Avaya IP 500v TDPS 138. I was extremely lucky, the reason was easy to find: the fuse burned out, and checking the AC input resistance showed an asymmetric value depending on the polarity of the tester. Comparison with a working module also confirmed that faulty part is somewhere in the input circuit. Suspicion fell on the diode bridge, and indeed, when I soldered out the GBU8K chip, one of its diodes was in a short circuit. Replacing of the diode bridge restored the operation of the unit.

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

Yes, exact same failure to the dot. There are four 10uF caps in parallel, which provide about 15VDC to the PWM's. The weird thing is that these caps aren't failing in a total short, rather fail in the 80 to 100 Ohm range. It does seem that this PSU model has a higher failure rate due to this. But it is easily fixed.

[sam_sam_sam]

Re: Delta TDPS-138AF Avaya no output repair

This is interesting that you had another power supply with the same exact issue again wow

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

Got another one of these funky PSU’s today on my bench. Same complaint, not working.
Guess what?! Yep, same darn problem. This time I went straight to those 4 SMD caps in parallel on the back side of the PSU. Measured like 80 Ohms across them. Sure enough the second one in was the problem. Replaced SMD cap, PSU fixed. Took 5 mins, lol. Seems like they have a weak spot there.

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

yes and thanks sam.

[sam_sam_sam]

Re: Delta TDPS-138AF Avaya no output repair

I also used this trick here on my arbitrary function generator: https://www.badcaps.net/forum/showth...ighlight=kuman

I remember reading this post before and I even made a comment about your repair

Thanks for sharing them

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

O.k. Sam...,
This trick is pretty much my last ditch effort to repair something, when I don't know where the short exactly is. However I do have to know what trace is shorted, for this trick to work. So troubleshooting is key. Also at this point the repair is an automatic 50/50 chance for me, although I do have a very high success rate that suggests other wise using this trick. After all I have to take stuff off the board, making sure nothing got damaged in the process.

Chasing a short, I take stuff off, one by one, trying to eliminate suspected problems on the shorted trace, 43 Ohms in my case. I try to be careful with the IC's and voltage regulators and take them off, but the rest not so much. Once I removed certain things and the short didn't go away, I look at the components, determent where to feed positive and negative and adjust between 5 to 12V, 0.5A to 1.5A from my CV & CC PSU, douse the board with IPA, wait anywhere between 30 seconds and 2 minutes and look for the bubbles or feel for the heat.

Now in this case there were no bubbles, because it was on the back side of the PSU and there were 4 caps in parallel, so the heat would spread over the surrounding caps. But it still got hot enough for me after 2 mins to tell with my finger that this was the place to remove all 4 smd caps even with my fingers on the other side of the circuit board. A quick check with the DMM revealed 43 Ohms there as well, so.... well the rest you know.
Feeding power to a SMD short is o.k, just don't feed too much power, rater wait for a minute or 2. Trust me, the shorted part will get hot as it has to dissipate all the power and create heat.

I also used this trick here on my arbitrary function generator: https://www.badcaps.net/forum/showth...ighlight=kuman

[sam_sam_sam]

Re: Delta TDPS-138AF Avaya no output repair

I had this type of issue with those type of capacitors on one of my Desoldering station controller board before I found it I started touching different components on the board and found a spot that was real warm and took my ESR meter and check it had 14 ohms of resistance on the power supply rail

It was not correctly controlling the temperature is why I was troubleshooting it in the first place

Plus every one in while it would just cycle the power supply

If I have this kind-a problem where it cycling a power supply I will try your little trick

“ Using this 91% IPA and feeding power trick, never gets old.”

I have one request can go into a bit of details of how you do this with out messing up the board

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

Lucky you, the owner didn't pick it up yet. Here ya go!

[sam_sam_sam]

Re: Delta TDPS-138AF Avaya no output repair

Came to find out that the problem is on the back side of the board, in 4 parallel SMD 11uF caps (the C912 group). One of them had an almost short. Put a used 12uF SMD cap in from a junker board, reassembled the PSU and Bingo! Works like a charm! :-D Frustrating little thing, but it was a doable repair without a schematic again.
Using this 91% IPA and feeding power trick, never gets old.
Case closed.

Could I trouble you to show on the board where the problem was

Thanks

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

All in a nutshell, the Delta TDPS-138AF power supply for the Avaya IP500 is fixed!

It's a pretty complicated power supply with 3 negative and 2 positive voltage rails. After a while of poking at it, something was dragging the Vin to the PWMs down. I had to remove quite a few things that were on that voltage line, but the short never went away. After removing all the more sensitive IC's and the little daughter board, I fed that voltage trace power with my lab PSU, cranked it to 12V and 1A, put some IPA on the board and watched, but no bubbles? Came to find out that the problem is on the back side of the board, in 4 parallel SMD 11uF caps (the C912 group). One of them had an almost short. Put a used 12uF SMD cap in from a junker board, reassembled the PSU and Bingo! Works like a charm! :-D Frustrating little thing, but it was a doable repair without a schematic again.
Using this 91% IPA and feeding power trick, never gets old.
Case closed.

Dang, now I am bored again... gotta find something else to put on the bench.

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

I guess our Province declared a state of emergency. Being bored, I put that PSU back on the bench for further investigation. I've got lots of stuff off the PSU, trying to eliminate a short I found going to the little daughter board. Dousing the board in IPA and feeding power from my lab PSU, I did find a shorted SMD cap in a parallel group of four C912 on the back of the PSU main board. Now I have to find a replacement for that shorted SMD cap put it back together and test again.

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

well, I put that PSU on the "fix later" pile for now. Thanks for everything RJ!

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

the PSU is apart at this moment. the 1207a is out and the daughter board too. i've had a few hard to work on power supplies, but i always got them going again. this one has me beat without any schematic to go by. I was thinking on fooling the PSU in a manner where i can turn individual power rails on, even without regulation, like i've done before.

[sam_sam_sam]

Re: Delta TDPS-138AF Avaya no output repair

Yes I know I have work on some switch power supply board that I have wanted to pull my hair out not that I have much hair left

[R_J]

Re: Delta TDPS-138AF Avaya no output repair

This is in reference to his comment earlier


This might be a real stupid question but what is the voltage at the optic sensors on the input side

Not really, I would have likely asked it next. It is a hard power supply to work on and even harder to try and trace the double sided circuit only with a couple pictures.