LM3886 issues

[Dougie085]

Ok, with the DMM in diode test mode I get 1.446 when connecting the positive lead to the neg leg and the neg lead to the pos leg. If I connect the pos lead to to the neg leg and then connect the neg lead to either of the center legs I get about half that reading. If I reverse the leads I get no reading. Does this seem backwards? Shouldn't the pos be connected to the positive rail and the neg to the neg? Or is this correct? If in fact the rectifier is good then I don't understand how it got so hot.

[Dougie085]

Well.... I plugged it in and was testing and I think I may of messed it up more. My lead slipped and shorted out 2 connections and now I don't seem to be getting much voltage. Thinking maybe the transformers are messed up. What I get for working on it with my kids hovering. Not sure how I'm going to pull that out and test them. Tried pulling the old rectifier out and don't think it's coming out lol.

[richie00boy]

The transformers may have survived as long as you didn't keep power on for long (i.e. less than 10 seconds). You probably just blew the recitifiers.

[Dougie085]

Well, it wasn't shorted for 10 seconds no....but it may of been on. I have one o the transformers removed so far..... whoever decided to glue all this stuff in is an a**hole.... Anyways what's the best way to test a transformer?

[BudP]

The transformer on the left appears to have a very messy and disturbed lead out. I cannot tell if the leads them selves are discolored and if the tape that wraps the toroid windings is discolored. I do notice that the transformer on the right has it's mounting glue intact and the one on the left appears to have lost that smooth glue coating. Am I being deceived by the picture or are these actual differences?

As for transformer testing, a simple ohms check, which if closely similar between known good and suspect channels, should be followed with a power on, no load check of voltages, which should be followed with a loaded check of voltages. The load should be at least from a 5 watt resistor and follow ohms law for R = E/I to obtain a proper size for the resistor.

It is quite possible that a semi blown regulator has overstressed one of the transformers and shorted the wires at the connection point, where toroid's are the most susceptible.

Bud

[Dougie085]

The one on the right is actually the bad channel, something heated up there and melted the glue so it smoothed out. I have both transformers out, I'm not sure what to do with this darn thing all this glue is really ticking me off lol. Thinking of just getting a bigger 21VAC transformer and running both amps off one instead of the dual mono setup. And then obviously a new case because this setup is just crazy.

I'll try testing the transformers later for now I'm tired of messing with it. Took me an hour just to remove them. I can't even get the rectifiers out.

[richie00boy]

Check the amps as posted earlier before you use more time and effort with the power supply. Can you power the suspect amp with the known good power supply and vice-versa?

[Dougie085]

Well I tested them with a DMM as suggested and they behaved as they should. At this point neither channel are working and pretty sure it's the rectifiers or the transformers....possibly both?

[Arx]

Originally Posted by Dougie085

Well I tested them with a DMM as suggested and they behaved as they should. At this point neither channel are working and pretty sure it's the rectifiers or the transformers....possibly both?

disconnect the power supplies from the chips, and check their voltages.

Linear supplies are pretty simple, usually they either work or they don't.