Delta TDPS-138AF Avaya no output repair

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

No, I did change the 1207A PWM and the comperator on the primary side on the little daughter board. Same result. The PWM isn't getting hot. It doesn't make any sense to me. There is another comperator on the backside of the main board, it also is on the primary. Haven't checked around there yet.

[R_J]

Re: Delta TDPS-138AF Avaya no output repair

Trace that line connected to the 51K resistor, something is drawing way too much current. If it was'nt the ncp1207a then it could be the DAP6A, it is a similar pwm ic.

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

the DAP6A has its own resistor same size, different value. Haven't gotten around to swap the DAP6A out yet, as I have to take the little daughter board out again. Its like something telling both PWM's to shut down. They don't even try to turn on.

[R_J]

Re: Delta TDPS-138AF Avaya no output repair

They both need to have the HV voltage at least around 50vdc so the startup cell can produce the vcc voltage.

For the 1207a PWM, I get 1.5V on Vcc and 17.5V on the HV pin.
On the DAP6A are 1.3V on the Vcc and 6.5V the HV pin.

The voltage on the HV pins are being loaded down by something, if it's not the ic it must be something else.

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

Yesteraday I went for why these big resistors heat up. Went to the 1207A PWM, checked again the path between it and the Mosfet it drives and nothing to be found. So I took the Mosfet out, no change. Took the new 1207A out and there was no more current draw on that 51k resistor. So removing the PWM does stop the current draw on the resistor. Put that 1207A back in circuit and voila, the resistor gets hot again. Haven't checked the DAP6A side yet, it functions the same way.

O.k. so lets say there is a problem with one of these PWM's, something is telling them both to not power up. An error on one side, should affect the other side of the PSU. I don't think that only a 2/3rds of that PSU runs, while the other 3rd doesn't on this PSU.

[R_J]

Re: Delta TDPS-138AF Avaya no output repair

The datasheet say's the ic will not operate with a vcc below 9 volts

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

I measured that 51k three different times and each time it measured 51k. Correct me if I am wrong, but lets say the resistor changes resistance under load (value going higher) it just would drop the output voltage but should not getting hot to the touch.

Earlier I had the 1207A out and before I replaced it with a new one, I had full power on both sides of the 51k resistor. I proceeded to check the DAP6A and it still loaded it's 240kOhm resistor down to 6.5V! Now why would that be, unless something is telling BOTH pwm's to shut down.

To recap: the 380v goes through the 51k resistor to the 1207A. The 380V go through a different 240kOhm resistor to the DAP6A.

[R_J]

Re: Delta TDPS-138AF Avaya no output repair

The ic's must be getting told to be turned off.
I re-check the math and 7ma through a 51k would result in a 357 volt drop (2.64 watts).
The dap6 must also be turned off and drawing about 1.5ma

It looks like both ic's can be turned off via pin2 (FB pin) So I guess pin 2 must be low on both ic's and could be controlled by a transistor somewhere, and something else could be telling that transistor to turn both ic's off

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

Yeah, that's what I am thinking, it's a feedback problem and the FB pins are low on both. I have to trace these FB pins where they go next. I was going to do that in my post 21, but anyway... gonna do it in a bit.

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

no dice. the fb pins go to these rectangular opto couplers on the back.

[R_J]

Re: Delta TDPS-138AF Avaya no output repair

That makes sense, but could there also be a transistor connected to them? the only way the optocouplers would shut down the two pwm ic's is if their leds were turned on and the photocel part would then be low resistance. If the led side has no voltage, the photocel side should read open.
What is the number on the optocoupler? Are they EL1018?
Which opto connects to which pwm ic?

It does look like the opto, ic602 could control the opto, IC603

[sam_sam_sam]

Re: Delta TDPS-138AF Avaya no output repair

if their leds were turned on and the photocel part would then be low resistance. If the led side has no voltage, the photocel side should read open.

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

[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.

[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

[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.

[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

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

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.

[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

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