Need help with Soundstream Van Gogh VGA800.2 amp

[jaimegmr]

I bought this amplifier to try to repair it, since it is supposed to be a very good amp. Opened it up when I got it and this is what I found:

Pictures:
Soundstream Van Gogh VGA800 2 pictures by jaimegmr - Photobucket

It looks like someone has opened it up before to try to repair it. The 8 transistors on the bottom of the main board appear to have orange-colored hardened flux or something on the pins.

The two obvious problems that I see with the board are the following:

• The largest inductor (L9) has one of the wires broken off where it goes into the board.
• The board is darkened in an area that has DZ53, DZ54, R27, R28, and R30. They all got hot when I powered up the amplifier.

Is the easiest solution for L9 to just wind up a new wire to replace the broken one?

What could be causing the diodes and resistors I described above to heat up?

I checked the LEDs when I powered it up and the Rail+ and the Power LEDs were turned on. The first time I made L9 touch the broken wire while the amp was ON. The second time that I powered up the amp after holding the L9 inductor in place, only the Power LED turned on.

Is there a service manual or schematics available for this amp (or any of the Van Gogh series)?

Thanks in advance.

[jaimegmr]

Mods please move this thread to the Car Audio forum.

Thanks.

[Eva]

The largest inductor is part of the power supply, it has one winding for each rail (positive and negative). When one lead becomes broken one of the supply rails becomes missing. This may produce further damage, such as overheating of components in the output stage, because when one rail is missing high currents may flow where they are not supposed to.

So first step is to repair the big inductor and check that both supply rails are in place. Then you can check for further damage.

[jaimegmr]

I connected the big inductor back in place by unwinding 1 turn from each of the two loops, so now they each have 26 turns instead of 27. The amp powers up and I got the following measurements:

GND to 1st coil of L9: -32.5V (first try), -47V (second try)
GND to 2nd coil of L9: 70V (first try), 52V (second try)
Approximately 100V across both coils.

Remote wire not connected: Power supply voltage 11.1V.
Remote wire connected (Amp ON): Power supply voltage 11.9V.

DZ53: 37.4V across zener diode, 38.3V after ~10-15 seconds.
DZ54: 37V across zener diode, 39V after ~10-15 seconds.

I measured different voltages at L9 each of the two times I tested it. The only thing that happened in between was that my power supply fuse (5A) blew up and I put in another 5A fuse, so I dont know if this has anything to do with the reason the voltages changed. The voltage across the two coils of L9 did seem to stay at around 100V both times.

I also noticed that the voltage at the input of the Amp was lower (11.1V) when the amp was off, than when the amp was on (11.9V). I did not check the currents, but this would lead me to believe that there is a higher current draw while off than when on with no signal input.

The voltage across the two 36V Zener diodes, DZ53 and DZ54, increased slowly. The longer I kept the amplifier on, the higher the voltage across the diodes went. It started out at around 37.4V for DZ53 and ended up at about 38.4V after around 10-15 seconds. For the DZ54 diode, it started out at around 37 and ended up at around 39V after 10-15 seconds.

[Eva]

One end of each winding on L9 has high frequency AC, resulting in non-meaningful multimeter readings (neither DC nor AC). The other end of each winding has valid DC and close to 0V AC. The "good" ends may be at opposite sides.

Zener diodes above 6V or so exhibit positive temperature coefficient, zener voltage increases more or less linearly as they heat up. Heating a 36V zener 30 deg.C can rise voltage by 1V.

You should measure amplifier current consumption with a multimeter, both turned on and off. Measuring a lower supply voltage when the amplifier is off is quite strange.

[Perry Babin]

Some meters will produce unreliable readings when there is more ripple (as you may have with the amp is on). That may explain the higher readings when the amp is on.

[jaimegmr]

I measured the gauge of the original magnet wire with a wire stripping tool and ordered what I thought was the correct gauge (18 AWG) to rewind L9. The magnet wire I received is much smaller than what was on there so apparently I messed up on the measurement. It looks like I need 16 gauge magnet wire instead.

Would you happen to know what the original wire gauge is? (If it is a commonly used wire gauge or something.)

[Perry Babin]

Do you have a dial caliper to measure the wire?

Are you sure that the wire you received is what you ordered?

[jaimegmr]

Unfortunately I do not have one. I've been meaning to get one for a while. I guess now is the time to buy one.

The wire I received is about 1mm in diameter and matches the AWG charts I've seen (1.02362mm). The one on the amp is just over 1mm, so I'm guessing it is 16AWG which is 1.29032 mm.

[jaimegmr]

I just measured the current of the amp and draws about 2.3A when On. The current draw when Off is to small to detect on the 10A scale of my cheap multimeter (burned the fuse on the 2A scale).