Repair Pioneer Receiver

[AltAudio]

Hello,

I was experimenting with a home-made voice coil and as I was sending signal to it via receiver, I heard a clicking sound at about 70% gain. When I hooked back the normal components, there is no sound. Figuring I blew a fuse, I took the top off and saw only 1 fuse(125V 8A) that appeared to be in perfect shape. So now it's a matter of testing various parts of circuit to determine which components went bad. I have multimeter and oscilloscope, but would like some input as how/where to start.

Many thanks...

 

[Nigel Goodwin]

Sorry, but it sounds like you've done somtething really stupid, and as a result blown the amplifier.

 

[AltAudio]

There are stupider things for sure. But I appreciate your candor - I think.

 

[transistor495]

This won't blow the fuse, but the amp chip itself, and normally there won't be any external evidence for this kind of failures

 

[AltAudio]

Is replacing it out of the question?

 

[KeepItSimpleStupid]

Troubleshooting AMPS is tough. Generally you have to get all the parts right or you let out the magic smoke.

Obtain a schematic.
Check power supply voltages.
Trace the signal by bi-secting every stage until it goes missing. Inject a signal and look for it at the tape out.
The protection relay will keep sound from reaching the speakers.
Check the DC output at the speaker terminals and before the protection relay.

A Variac helps when bringing up and amp fro the first time. One of the more critcal voltages to look for is the voltage between the 2 bases of the output transistors. Depending on the design, it's usually around 2x a typical diode drop for bipolar transistors. 1.2, 2.4 or 3.6 V.

If zero, there is a problem with the biasing. If higher than the value, then thermal runnaway can happen really quick.

 

[OlPhart]

Probably stereo, does 1 channel work? If so, use it to backtrace / compare from the output and move upstream.

Building your own stuff entails having test signal generators, amplifiers etc. It's best to have these objects both well protected from errors And well documented, so you can fix them When the protection isn't enough. G.H. <<<)))

 

[unclejed613]

what model pioneer?

rather than a variac, it's usually better to use a "lamp tester". you need a power cord, lamp socket, switch and outlet. the neutral side goes straight through from the power cord to the socket. the hot side goes power cord>switch>lamp socket>outlet. for a 100W/ch amp, you screw a 100W lamp in the socket. for a larger amp, use a 150 or 200W bulb. plug in the amp to the outlet and replace any blown fuses. what will happen when you turn the switch on, and turn on the amp power, if nothing is shorted, the bulb will light briefly and go dim. if something is shorted, the bulb will grow brightly, and the line voltage to the amp will be minimal.