[Redzilla]

Does anyone have a schematic for the servo dynamics SD1525-10 servo amp? or know what usually goes bad on them? I have 3 I'd like to fix for spares I can't see anything physically burnt on them. Thanks

[mike_Kilroy]

The TO220 output FETs under the pcb typically blow open.

[Redzilla]

The TO220 output FETs under the pcb typically blow open.

Are you talking about the four MJ11032 bipolar transistors mounted on the back? And is there anyway to test them with a DMM I'm getting the same reading when I test from base to emitter as I do from emitter to base does that mean they're shorted? I'm getting a ground fault led when I put power to it and it blows the fuse on the power supply.

[mike_Kilroy]

ok, the TO-3 in that case; most of these lo volt models use TO-220 fets, but if you say they are TO-3, ok. It has been years since I looked at that model, and dont feel it worth digging one out to double check.

So you want to check it. You provided enough info now to do so. if a fuse blows right away THEN ONE IS SHORTED - not an open issue.

To easily check (I know, telling this shoots myself in the b@alls since one of businesses is repairing stuff like this, but....)

OHM from dc bus + to each output.
OHM from dc bus - to each output.

if ANY reading is not really really high, you have identified the shorted ourput device. really really high means not 1-30 ohms (do the math - what size fuse is popping on what voltage supply? THAT resistance I=V/R blows the fuse.....

also OHM from each dc bus and each output to GROUND to make sure no shorts there....

One of these OHM tests will show you the lo ohms or your fuse will not likely blow.

[Redzilla]

ok, the TO-3 in that case; most of these lo volt models use TO-220 fets, but if you say they are TO-3, ok. It has been years since I looked at that model, and dont feel it worth digging one out to double check.

So you want to check it. You provided enough info now to do so. if a fuse blows right away THEN ONE IS SHORTED - not an open issue.

To easily check (I know, telling this shoots myself in the b@alls since one of businesses is repairing stuff like this, but....)

OHM from dc bus + to each output.
OHM from dc bus - to each output.

if ANY reading is not really really high, you have identified the shorted ourput device. really really high means not 1-30 ohms (do the math - what size fuse is popping on what voltage supply? THAT resistance I=V/R blows the fuse.....

also OHM from each dc bus and each output to GROUND to make sure no shorts there....

One of these OHM tests will show you the lo ohms or your fuse will not likely blow.

Ok thanks for the information I really appreciate it!
I will check it out and see what I come up with, and it's a 3A fuse, thanks again

[Redzilla]

Ok I tested it like you posted I'm not getting any real low ohm readings anywhere they're all in the M and K range, no dead shorts that I can find, I've tested all of the diodes and resistors and I don't see anything visually burnt or any broken solder joints, I don't know what to check next?

[mike_Kilroy]

I didnt think of the obvious: did you ohm directly across dc bus +&- power input pins?

[Redzilla]

I didnt think of the obvious: did you ohm directly across dc bus +&- power input pins?

I can't remember if I did or not, I'll check it when I get home and report back, thanks

[Redzilla]

I can't remember if I did or not, I'll check it when I get home and report back, thanks

It checks good both are in the M, I did find that the collector closest to the power terminals is shorted to ground it looks like the plastic film under it is cracked, is this most likely my problem?

[Redzilla]

Mike thanks for all your help! The collector on 1 T03 transistor was touching the metal frame that it bolts down to is all it was I unsoldered it and put a dab of heat sink grease on both sides of the plastic film reassembled it and it works great! now I've got 2 more to tackle but at least now I know what to look for, thanks again Mike

[Redzilla]

https://www.google.com/url?sa=t&source=web&rct=j&url=http://diagramasde.com/diagramas/aires-acondicionados/SD%25201525.PDF&ved=0ahUKEwjpgtKXn5fMAhUBFT4KHbohA oY4HhAWCCUwBQ&usg=AFQjCNFhUHr55iP6y3zqusv2jI5qahy7 LA&sig2=VLVzKQN-4Er6MmfMGgvIBA

[willamwang]

The TO220 output FETs under the pcb typically blow open.