Delta TDPS-138AF Avaya no output repair

[CapLeaker]

I have this Delta TDPS-138AF B out of a Avaya phone system here for repair.
Symptom: no output power on any of them rails.

Fuse is good, PFC is working as I have 384VDC laying on the main filter cap, it draws about 4W from AC mains, heat sink on the main section gets warm, but I'll be damned to get anything out from any rail on the secondary. There aren't any shorts on the secondary, diodes check good and the fets check good too. Checked the gate resistors and those check out as well. Also checked the transformers if the little thermal fuse is open, but no dice there either. Now I think is has something to do with the driver card.

There is a driver card soldered into the middle of the PSU. It consists out of a PWM for the booster, op amp, timer and comperators. Complicated thingy!

Anyone has a schematic for this PSU would be greatly appreciated!

[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

Looks like I do have a bad transformer. Ugh!

[R_J]

Re: Delta TDPS-138AF Avaya no output repair

I would doubt the transformer is bad, do you have a scope? If you can't check the drive signal to the fet, it's hard to say where the problem is. If the pfc is working, then what is the number for the drive ic that drives the fet. that drives the primary?
an open transformer is easy to check, and a shorted turn would likely blow the fet or fuse at a minimum.
Whats the number on the 2 ic's on the primary side of the sub board? one is a 14 pin the other is an 8 pin.

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

The transformer is more brownish colour than the other two. It’s not open, but looks kinda burnt. The relay is not getting energized, but testet ok out of circuit. If the power supply is working correctly, it would bypass the inrush current limiter. There is a high voltage x cap 105k, which would provide power to the relay, had that out too and tested ok. Pic #4 left IC is a pwm. On the right a comperator. That is the only PWM on that whole power supply. I think that is for the PFC. The all the rest of the IC’s are op amp, timer and comperators on that daughter board. All other IC’s on the PSU are comperators as well. Never seen a design like this from Delta. I did check the gate drive resistors and these check out as well. Now here I get lost on how the PSU is supposed to be working with only one PWM. I’ll get back later with the number of that PWM.
Second thought, if that PWM isn’t for the PFC, then how is that PFC boosting?

[R_J]

Re: Delta TDPS-138AF Avaya no output repair

The pfc will always be on for this power supply.

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

On the back side of the PSU is one IC and that is a comperator as well. Yes, as soon as I plug the PSU in, there is boosted voltage on the main filter cap @ 384VDC. That is all the PSU does at the moment. I’d really like to find a schematic for it, as it is a very complicated PSU. There is no starter cap etc, like one would find on a regular PSU.

[R_J]

Re: Delta TDPS-138AF Avaya no output repair

It looks like it is an always on power supply (no on/off control) It also seems to have two seperate outputs, one for +3.3v +5V and the second for -28.5, -48v, -110v
Do you know if it has a power supply on/off pin? it does'nt seem to.
They are not that expensive to replace.

[sam_sam_sam]

Re: Delta TDPS-138AF Avaya no output repair

I am watching this post I have not seen a power supply quite like this one

So I hope you can fix so we can all learn something I am meaning this in a good way

Thanks for sharing this power supply repair attempt good luck with it

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

Yes, it is a odd design Delta PSU. It is always on, doesn’t have on/off anything (it’s always on), but it has a “power good” line. I know they can be had for a 100 bucks, but that is beside the point. This is something so oddly designed, I had to post it. Would be nice to figure out how this thing works.

[sam_sam_sam]

Re: Delta TDPS-138AF Avaya no output repair

Yes, it is a odd design Delta PSU. It is always on, doesn’t have on/off anything (it’s always on), but it has a “power good” line. I know they can be had for a 100 bucks, but that is beside the point. This is something so oddly designed, I had to post it. Would be nice to figure out how this thing works.

What does each power supply rail power on this phone system do if you know

Now what fun would be if you just bought one to fix the phone system problem

[R_J]

Re: Delta TDPS-138AF Avaya no output repair

It could be setup so the 3 & 5 volt sections come on before the 45 & 110 ring voltage section turns on.

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

Some good news:

I am getting somewhere! I had to find my microscope, did some cleaning on the board and now things make sense. I couldn't see the IC's part numbers on the PSU properly. There are 3 PWM's in total. One for the PFC (L6562D on the daughter board), another one for the 3,3 and 5V rails ((NCP)1207A) and a third PWM for the negative voltages (DAP6A) (should be the same as an NCP1200 60khz?).

My bet is that the PWM for the 3.3V and 5V rail (NCP1207A) is dead.
Have to look at that with an O'scope later and see what happens around that PWM.

[R_J]

Re: Delta TDPS-138AF Avaya no output repair

On the NCP1207A, check the voltage on the pins (don't slip) pin 8 should have full high voltage and pin 6 should have the vcc voltage, this one is the key, it should be around 12 volts, if it is 0 or 5 volts, there is a problem. Also check the fet it drives, and its source resistor.

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

that is easier said then done with that stupid daughter board installed. I guess I have to either guess the PWM is at fault, or I have to solder little wires to it.

[R_J]

Re: Delta TDPS-138AF Avaya no output repair

It should only take one wire for the vcc. Which ic is it? the one next to pin 13 of the daugter board? there are 2 mlcc's connected to that ic pin6.

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

yes, you see the IC on pic 4, right next to pin 13 of the daughter board. That daughter board is so close to that IC, it's not funny.

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

Did some measurements on the two PWM's on the main board.
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.

[R_J]

Re: Delta TDPS-138AF Avaya no output repair

The HV lines are too low for the ic's to work, where does it get the HV from? It could be an open resistor from the HV source to the ic.

[CapLeaker]

Re: Delta TDPS-138AF Avaya no output repair

This is another funny part. The DAP6 goes via 2 resistors (second big one) to the transformer behind it. That resistor get hot, but not as hot than the one for the 1207A.
Now the 1207A traces back to the big pink resistor (51kOhm) next to the AC stage (or next to the main filter capacitor), it also splits there to two rows of resistors (2 in series each row) going to pin 2 and 3 on the daughter board. The big 51kOhm resistor, something is drawing current like crazy. Makes 385VDC go down to 17.5V and heats the resistor so you can't touch it.

[R_J]

Re: Delta TDPS-138AF Avaya no output repair

It could be that the ic is shorted, they usually don't draw much current as they are only a driver ic. I would think the ic would also be getting quite hot