JVC JR s600 blows 8 amp fuses.

[srinath]

At power up it kills the 2 8 amp fuses. It also makes no sound. However its main fuse the 10 amp one is intact, all the lights light up and it seems to be tuning in to radio. The signal strength etc move and so on with the tuning wheel.

Could someone shed some light on it. A schematic would also be nice to find.

Thanks.
Srinath.

[nigelwright7557]

Most likely output transistors gone short.

I would guess if the main fuse is OK then power supply is fine.

[srinath]

Its got those TO-3 type output transistors. I tested all of em albeit not with my newly acquired transistor tester but with the multimeter in the diode setting. They all tested OK.
Its safety relay clicks (That is a surprise) and it shows no DC at speaker terminals on the speaker 1 terminals and ~.021 V and .016V on the speaker 2 terminals.
I will be yanking them and testing with my transistor tester when I get some time.
Thanks.
Srinath

[sakis]

then it could simply be the rectifier ....if the rectifier is shorted ( and often that means that other circuits radio and pre are working on other power supplies ) \\

but wait ...the safety relay cliks without the power fuses ??? yes that could be also possible i think ... so seperate main amplifier from its power supply and see what hapens

kind regards sakis

[srinath]

Thanks so much sakis. That is an easy one to try.
The amp first time I tried it with new fuses blew the fuse and the circuit breaker in my room. Of course after that I plug it in outside my house on a dedicated spike buster.
Thanks so much.
Cool.
Srinath.

[srinath]

Across the input filter caps - the 22000 uf ones I read a momentary 120 ohm resistance across one and a steady 4.1 ohm across the other one. I believe a DMM uses DC voltage, and a cap should be impervious to DC and hence the steady 4.1 ohm has a dead short in it. Is that about right. Thanks.
Cool.
Srinath.

[pinyoro]

I have seen a case where a DC filtering Cap (22000 uF in your case) where short circuit. If the T03 output transistors are fitted in sockets, I would take them out making sure you note their original position (Youd have to apply fresh heat sink compound after removing old paste though). Check resistance across caps. If it doesn't increase disconnect bridge rectifier then check resistance accross caps again. If very low resistance is still there then likelyhood is that smoothing caps are faulty although this is rare.

Originally Posted by srinath

Across the input filter caps - the 22000 uf ones I read a momentary 120 ohm resistance across one and a steady 4.1 ohm across the other one. I believe a DMM uses DC voltage, and a cap should be impervious to DC and hence the steady 4.1 ohm has a dead short in it. Is that about right. Thanks.
Cool.
Srinath.

[srinath]

Oh that is a neat trick. Let me repeat this to make sure I understand.
1. Mark the locations of the output transistors.
2. Remove them.
3. Measure the resistance across the 22000 uf caps again. If it increases the output transistors are bad - or one or more of them is bad.
4. If not increase, then remove the rectifier bridge and measure the caps resistance again. If it increases, the rectifier bridge is bad, if it doesn't increase the cap is bad.

Is that about right ?
I will do it tonight.
Thanks so much.
Cool.
Srinath.

[pinyoro]

What you have written is correct. It is a case of tracing the source of the very low resistance.

Originally Posted by srinath

Oh that is a neat trick. Let me repeat this to make sure I understand.
1. Mark the locations of the output transistors.
2. Remove them.
3. Measure the resistance across the 22000 uf caps again. If it increases the output transistors are bad - or one or more of them is bad.
4. If not increase, then remove the rectifier bridge and measure the caps resistance again. If it increases, the rectifier bridge is bad, if it doesn't increase the cap is bad.

Is that about right ?
I will do it tonight.
Thanks so much.
Cool.
Srinath.

[srinath]

OK I separated the 22000 MFD caps from the board. The cap I got low resistance had the same resistance as the other cap. Then I checked it across the terminals and it was low. Then 1 by one I pulled the power transistors out and measured the resistance across the terminals and tested the transistors themselves. They all tested perfect and the resistance in all cases was the same low number.

It started to rain before I got any further, so I got it back in the house.
I go looking for a rectifier bridge next. Thanks for all the help.
Cool.
Srinath.