Help track fired part in schematic

[Bonsaimaster]

I have build two  compressors boards. One is working great the other not. Because the power supplies have opposite connections on the PSU, I think the non working board got fried when I tried to hook it up with the wrong connector, just not sure where. Anyone what to help me locate the problem. I am including a PDF of the schematic. Working board voltages are written and NON working board voltages in Parenthesis. I am not good at reading schematics but I think the problem is in BC 214 and/ or BC 184. Any help appreciated.

Bonsaimaster

 

[joaquins]

Where are the voltages referenced at? For me looks like some nodes have two different values and not always match... D13 cathode is connected directly to ground and shows -4.6V in the working unit. I guess it's a typo and you measured it's anode.  colector and emitter are mislabeled on the BC214, emitter is always the one with the arrow, no matters if going in or going out 

I would start changing the transistors, Diodes looks fine which is odd if you connected the supply backwards, D14 and D15 did suffered quite an abuse of almost half an amp. Remove the transistors and test them outside the board, I would use all new and save the ones that didn't released the magic smoke for a less critical application, since BE junction polarized backwards make some bad things with transistors even if they are not fried. 

JS

 

[PRR]

Aside from the C-E swap, I bet you mixed-up VT25 and VT26.

The VT25 Emitter (or some pin) is nailed to ground and should show Zero Volts.

One end of D13 goes to ground, (0.0V) yet you show 0.8V.

I can't make sense of this until you sort it out. (Well maybe I could but it would take a very long time to reverse-engineer the mix-ups.)

I _do_ like that you put voltages ON the plan. (Separate plan and volt-list gives me tennis-neck.)

I _do_ like that you gave the "good" voltages. This is often an excellent clue. However the "right" voltages are fairly obvious (after an initial head-scratch) so it might be clearer now with just the bad voltages (but for the right parts and pins).

Re-re-check D13 voltages.

Replace VT25 and VT26 with any jellybean transistors. Note that one is NPN and the other is PNP, and *get them right*-- right places, right pins in right holes.

> Diodes looks fine which is odd if you connected the supply backwards, D14 and D15 did suffered quite an abuse of almost half an amp

Easily explained. A backward Zener is a plain forward diode. Will drop 0.6V. Will heat-up like 0.6V*0.5A or 0.3 Watts. That won't cook. R77 took the brunt of the abuse. For now, we still have the 22.8V up there so it isn't burned-open, but I'd take a critical look and replace it for any sign of heat. It idles at 0.45W so it needs to be a 1W part, and 2W would be better.

 

[Bonsaimaster]

Sorry the voltage on the ground of the diode is labelled wrong.

VT25 and VT26 are in properly

The voltages were not reversed but were connected like this.

PE had +28V
-28 had GND
GND had -28V
+28 had PE

Thanks for the help

 

[joaquins]

Sorry the voltage on the ground of the diode is labelled wrong.

VT25 and VT26 are in properly

The voltages were not reversed but were connected like this.

PE had +28V
-28 had GND
GND had -28V
+28 had PE

Thanks for the help

I guess PE and GND are connected somewhere, then the abuse was only for the lower side of the circuit. VT25 and VT26 where reverse biased, I would start changing VT25 first as most suspicious.

Aside from the C-E swap, I bet you mixed-up VT25 and VT26.

The VT25 Emitter (or some pin) is nailed to ground and should show Zero Volts.

One end of D13 goes to ground, (0.0V) yet you show 0.8V.

I can't make sense of this until you sort it out. (Well maybe I could but it would take a very long time to reverse-engineer the mix-ups.)

I _do_ like that you put voltages ON the plan. (Separate plan and volt-list gives me tennis-neck.)

I _do_ like that you gave the "good" voltages. This is often an excellent clue. However the "right" voltages are fairly obvious (after an initial head-scratch) so it might be clearer now with just the bad voltages (but for the right parts and pins).

Re-re-check D13 voltages.

Replace VT25 and VT26 with any jellybean transistors. Note that one is NPN and the other is PNP, and *get them right*-- right places, right pins in right holes.

> Diodes looks fine which is odd if you connected the supply backwards, D14 and D15 did suffered quite an abuse of almost half an amp

Easily explained. A backward Zener is a plain forward diode. Will drop 0.6V. Will heat-up like 0.6V*0.5A or 0.3 Watts. That won't cook. R77 took the brunt of the abuse. For now, we still have the 22.8V up there so it isn't burned-open, but I'd take a critical look and replace it for any sign of heat. It idles at 0.45W so it needs to be a 1W part, and 2W would be better.

I was thinking about over current, not over power, which may be a problem in some cases, but I don't know the current rating for the specific part.
I also commented on more than one different voltage on the same net, AGND is the one with more different voltages...

Bonsaimaster, please re check the voltages and we look again...

JS