Still trouble with the A600

[corradolvr]

I have replaced all the power transistors and checked the power supply. The supply is fine. I power the amp up and it turns on now without the over current light coming on. When I put a 1khz tone on one channel it works great, but the other channel doesn't have any signal. The A1011 and C2334 transistors on that side get really hot. I monitor them so they don't get to hot. On that same side I did manage to blow one of the BDT81 transistors again but was easily able to find and replace it. I tested for input and output on the vertical boards on the 3rd leg from the ends of each card on the o-scope. They check good with gain. Does this sound like I may have replaced a bad transistor with a bad transistor? What could cause this? The BDT81's right behind the power and low impedance led's look like the got really hot at one time. The trace got some what exposed but I ohmed it out and it checked ok. Where should I go from here? When I power up the amp now it starts out drawing about one amp. After it warms a little my current limit on my power supply comes on. I have it set really low so the amp won't further damage itself. My Huntron Tracker's display went out. AAAAAAHHHHHHHHHHHH! This amp is driving me crazy. Does anyone have any ideas based on the symptoms. I've never had an amp give me this much trouble before. It's especially irritating because it looks so simple compared to what I work on for a living.

Thanks,

Corradolvr

 

[Jebomater]

Sorry i cant help, but i take it you have a corrado? g60 or vr6?

I have an 96 mk3 gti vr6. Its pretty fun

 

[corradolvr]

92 vr6 second car. You can't own one as a first car unless you're loaded . Thanks for checking my post!

Corradolvr

 

[Perry Babin]

I finally found the driver board schematic I was looking for. This was posted by someone else.

http://www.diyaudio.com/forums/attachment.php?s=&postid=1128157&stamp=1170949161

With this, it should be a simple matter to find where you're losing signal.

 

[Jebomater]

haha, Yeah corrado's do tend to break down alot

 

[corradolvr]

Thanks for the schematic. Am I correct in thinking that the input and output to the vertical boards are the third pin in from each end? An amplifier repair shop lead me to believe that. Does anybody else have any ideas? does anybody know what that red LED in the center of the board is for? I've never seen it light up.

Thanks,

Corradolvr

 

[Perry Babin]

3 is likely the input. 12 and 13 are the outputs. In an amp that's operating properly, the same signal is likely to be seen on pins 3 and 9. Pin 13 will drive the drivers connected to the positive rail. Pin 12 will drive the drivers connected to the negative rail.

In most amps, the input is fed into one side of the differential amp and the negative feedback signal (from the amplifier's output) is fed into the other side of the differential amp.

On a few amps, the input signal AND the negative feedback signal are fed into the same side of the differential amplifier. When the input is fed into the inverting side of the differential amp (the pin 9 side), the output is going to be inverted (180° out of phase). This is how Rockford inverts one of the channels in their amplifiers.