Newbe question-troubleshooting power transformer

[Mbira]

I know this has been covered before, but for the life of me, I can't find it.

I think I have a bad power transformer in this SWR amp. It blows fuses and fries power transistors, but only after a few seconds of being on. I'm used to seeing a bad power transistor blow fuses instantly. I have checked all diodes and resistors.
Can I measure the power transformerr with a DMM and see if it is working? It does look a bit toasty. I don't have a variac at this time...

Thanks as always,
Joel

 

[CJ]

Just disconect all wires on the load side, plug it in, and see if the fuses pop.
If it's an internal short in a winding, it should blow thew fuse.
If it does not blow the fuse, leave the wires dis-connected and measire all your ac voltages.
if everything is cool, the problem is in the circuit most likely.

 

[Mbira]

Thanks CJ. I was confusing myself because this is one amp and then a seperate "powered monitor" amp. They were both almost having the same symptoms. I disconnected the wires to the seconaries of one PT and fuse blows-bad iron. The other, I disconnected and fuse and AC is good-so looks like I had two different problems...
Thanks again.

PS: since othe one amp was blowing output transistors and those buggers are expensive, can I power up the circuit with those transistors removed and check voltages, or will I damage the driver transistors, etc?


Joel

 

[CJ]

Usually those transistor output stages are direct coupled, so you might not do damage, but you will have a hard time checking the driver circuit without new pwr transistors installed.

 

[Mbira]

thanks... :guinness: