Bowing 800ma with shorts reading across primary of power supply

Maybe there could be one set of 2SA1962 pnp and 2SC5242 npn transistors shorted thats what i think inside on the output stage . try to measure for short circuit on every 3 B-C-E base collector and emitter . but rememer to try to find the cause of the shorting. .
if left channel is shorted or right you will have to solder out and replace the defective parts. a variac or make a test unit that you will power the amp over a 200 watt lamp because of the fuse that will bow out again BUT if you have a primary problem in the power supply then measure the bridge rectifier (or 4 bridge diodes) and also the capacitors and also .observe for leakage because that leakage could damaged the electro conductive tracks, and clean the print always after repair.

have the unit opened and check for the blow out fuses..

If the 4Amps fuse should bow up, there should be a short circuit in the circuit after it. Check all the rectifier diodes for short. If a stalk rectifier is used, check it. Check the veristor [over-voltage protector; connected across AC input] after the switch for short. The schematic is in PDF, and cannot upload to you by this window. If you wish to get some details, check the site linked here. It has power supply section circuit to many brand TVs. Search the site, with the switching control IC. It will make search easy.
http://electronicshelponline.blogspot.com/

Were the bows numbered by chance? Any time these old style headerliners were removed the bows were tagged with numbers

Fuse blowing is due to excessive current drain and the the first clue is the blown fuse itself. If the fuse blows with a flash a bang and splatters copper across the inside of the glass you have a hard blow caused by a dead short on the power supply, check for power switch flashing over internaly. Short circuit main filter capacitors. Shorted turns in power transformer primary winding. If fuse just separates check for short on output transistors C to E. Try isolating fault by disconnecting LT pos/neg supplies to output stage. Also check for partial shorts on speakers and speaker wires using an analog ohm meter on low ohms setting.

Check your all capasitors of pwd supply any capasitor is lickege or short or not work poperly if you cann't find any problem replace your all capasitors of pwd supply

Hi radek

If it is a toroidal,they have a nasty habit of going shorted turns on the primary. Is it blowing fuses? Let me know

robotek
ex In'gill ;)

Does it attempt to startup at all? Do you get any lights or any indication that the unit is trying to start? If not, there should be a small transformer inside that is the standby transformer. It generates the 5V standby voltage. I have seen these go open in the primary since there is a fuse built into the transformer. You may need to replace this transformer. You should be able to get to the primary winding. With the unit unplugged, measure across the primary side with an ohmmeter. You should read a low value. If it reads infinity, the primary is open and you need to replace the transformer.

Dan

Hi there. From memory they had bridge rectifier problems with them going short circuit. Check them first. Sometimes the toroidal transformer can go a shorted turn, in turn blowing primary fuses. try to soft start it whilst it is blowing fuses, Best bet is to make up a special lead that has a 60w light bulb wired in series with the mains power supply(or across the fuse holdwer that is blowing:). Limits the power in the circuit to ... well you guessed it 60 watts.

check em out and let me know.

regards
Graeme

This can be caused by too low of an impedance from the way the speakers are wired, bad speakers, crossed/shorted speaker wires, and sometimes even a poor charging system (if the amp goes into protect when the volume is turned up) and is usually what the problem is 95% of the time. As you said, very possible to be shorted output devices or shorted power supply rectifiers. Beyond that, it could be a shorted filter cap, some sort of short across the power rails, some sort of short across the output, shorts across the primary. And of course loose hardware - any missing screws or nuts? A loose one under a pc board can short out most anything.