Please help me fixing my Jvc ax1100,

[sonci]

Ok, I searched for weeks Audiokarma, trying to fix it by myself, but the beast just stays in protection, so I'm starting this thread.
It happened when I tried to set the idle current, the trimpot went open, maybe because I had sprayed it with Deoxit, there was a puff, smoke and protection kicked in.
Even though there was a bad smell I didn't see anything burnt on the pcb. The manual seems too complicated so I had to measure everything, and there are a lot of components on this amplifier.
Of course the output transistors of one channel were blown, a pair of Toshiba 2SD1148 and 2SB863, also I identified 3 burned resistors.
R516
R522
R528
the transistors Q516, Q518, Q520,Q522,
2SD1148 I used ONsemi NJW0281G
2SB863 I used ONsemi NJW0302G , as recommended here on a similar thread. The trimpot was Vr502, it measures ok now.
I replaced resistors and transistors but nothing has changed, it stays in protection. The voltages between transistors legs seem identical for the equal pairs.
I have read that in dynamic super A amplifier with blown output, the chip IC 502 (vc5022-2), can be damaged too, but when I test it with multimeter in diode mode, it measures the same as the other chip.
There are no technician for this kind of work near me, and I really want to fix it, since this was my fault.
Any help?

 

[slimecity]

Have you also replaced the bias trimpot?

Search on this site for instructions on building a dim bulb tester - and only power the amp up thru that from now on.

 

[petehall347]

RT502 pin 3 voltage ?

 

[sonci]

Have you also replaced the bias trimpot?

Search on this site for instructions on building a dim bulb tester - and only power the amp up thru that from now on.

I haven't replaced the trimpot because it seems to measure ok now, but I'm going to do ii eventually.
I thought there was no risk when the amplifier is in protection mode, but maybe I should use a bulb tester.

RT502 pin 3 voltage ?

sorry but I'm just a guy with a multimeter, you mean R502 near the trimpot?

 

[petehall347]

no .i mean the plug next to the output transistors . pin 3 is audio out and should be close to 0v dc .

 

[sonci]

no .i mean the plug next to the output transistors . pin 3 is audio out and should be close to 0v dc .

ok, with the black multimeter plug to ground and red to the out pin, dc is around 0.00,
while there's high dc between B and C leg of transistors (NPN) around 60v, but probably this is normal because it's the same for both channels..

 

[petehall347]

now try dc like i said .

 

[sonci]

now try dc like i said .

sorry, both are 0V

 

[petehall347]

relay should click in then ..try getting voltage same point for other channel
when checking transistors go from base to emitter ..most cases you should see around 600mv .

 

[sonci]

relay should click in then ..try getting voltage same point for other channel
when checking transistors go from base to emitter ..most cases you should see around 600mv .

From base to emitter is around 120-170mv but I cant be sure because the value fluctuates a lot, for all transistors.

 

[petehall347]

are they plugs where you measured 0v ? if so unplug them and power up unit and see if relay clicks .

 

[OMGCat!]

I haven't replaced the trimpot because it seems to measure ok now, but I'm going to do ii eventually.
I thought there was no risk when the amplifier is in protection mode, but maybe I should use a bulb tester.

The relay only disconnects the speaker outputs so you can still damage components while poking around in there. I'd definitely use a dim bulb tester to do any further troubleshooting as if you have a shorted device somewhere you can be stressing more and more stuff each time you turn it on.

 

[sonci]

are they plugs where you measured 0v ? if so unplug them and power up unit and see if relay clicks .

I don't see any plug here.

The relay only disconnects the speaker outputs so you can still damage components while poking around in there. I'd definitely use a dim bulb tester to do any further troubleshooting as if you have a shorted device somewhere you can be stressing more and more stuff each time you turn it on.

I'm doing it, thanks.
PS. I never thought it would be this hard to find an old 60 or 100w lamp!

I also get some low readings from Q514, if comparing with Q513. Is this a driver transistor? If it's short, is it possible to trigger protection?

 

[sonci]

I connected the dim bulb tester. Initially there is a strong light for maybe a fraction of a second, immediately after turning on, then the bulb stays barely light, so I know I'm not destroying more..
I still suspect the Dynamic Super chip, even though when testing between legs(9), in diode mode, values are nearly the same with the other chip, except for pin 1 and 5.
I tried again what Pete sugested, and it seems that dc value rises from 0 to around 240mv, but I don't know if its correct or its a multimeter problem, because it seems to fluctuate.

 

[petehall347]

what voltages at other pins ? 1 and 2

 

[sonci]

what voltages at other pins ? 1 and 2

Ok, Ground to pin 1: 52v
Ground to pin 2: -62v
Ground to pin3 (audio out): rising to around 230mv.

 

[petehall347]

is it same both channels ?

 

[sonci]

is it same both channels ?

Unfortunately values change for different grounds, I thought the ground is the same in the pcb, but it seems this has 2 or more grounds.

 

[petehall347]

use power supply ground

 

[sonci]

use power supply ground

Thanks for helping me mate.
Can you be more specific, you mean some black wire going from the big capacitors?
I have to turn upside down, because the psu cables are soldered on the back of the pcb.