soundstream van gogh 800.5 turns off...

[fs1lag]

good morning,

I own a soundstream van gogh 800.5 amplifier which has served me well for a very long time. A couple of months ago, it started dropping out, going into protection i suspect. So, i opened it to find out what's wrong. I found out that the large metal pieces which transfer signals to another part on the mainboard were a little loose in some places so i added some extra soldering. After this action the amplifier worked great again for half a year i think.

Now, i'm experiencing the same problem, only difference, the complete amp stops after it had a mechanical shock, when i drive through a gap in the road or a speed bump. Usually it does not come on again... So i opened it again yesterday and tried to do the same as i did before but unfortunately no succes :-( It keeps doing the same, now lying on my desk in a test environment i've noticed that when i tap it with my fingers it drops dead, when i tap it again in most cases it comes on again...

I've redone all soldering so i'm quite doubtfull that that would be the cause. Do you have any ideas, might there be a broken component of any kind?

I live in Belgium and my native language is Dutch by the way ;-)

best regards, Bart

 

[Perry Babin]

With an insulated probe, tap on each of the busbars very lightly. If you find one that's more sensitive (takes less to make the amp shut off), it may be the one with the bad connections.

Many times, it's not enough to only add new solder. Often, it's necessary to do the following to get a good connection:

Desolder and remove the busbar
Desolder the lead of the busbar completely (desoldering braid works best)
Sand the terminals to bare metal to well above the terminal
Re-tin the terminals
Desolder the board thoroughly
Reinstall the busbar and solder it on the top and bottom of the board

This will generally prevent the connections from failing again.

 

[fs1lag]

i'm afraid the problem has evolved.. nothing helps anymore, when connecting the remote i just hear a relay clicking and that's it ;-) nog lights anymore what so ever..

i could really use the schematics at this time i've sent an e-mail earlier this morning to (well i guess it was you looking at your nickname) ask someone if he could help me out..

otherwise i'll have to give it to a repair shop...

 

[fs1lag]

voltages on the sg3525:

1: 2,58V
2: 4,48V
3: 0,02V
4: 0,22V
5: 2,06V
6: 3,78V
7: 2,04V
8: 4,91V
9: 0,47V
10: 0,19V
11: 0,00V
12: 0,00V
13: 10,42V
14: 0,00V
15: 10,92V
16: 5,17V

power supply voltage is 12,2V (B+ and remote)

 

[Perry Babin]

Pin 9 is near ground. That's why the IC has no output. The input to the error amp should cause pin 9 to swing high so either the IC is defective (not likely) or something is pulling the voltage on pin 9 to ground. Can you follow the traces back from pin 9 to determine what's pulling it down (transistor, op-amp...)?

 

[fs1lag]

hm.. only components directly connected to pin 9 are resistors and capacitors..

An externally hosted image should be here but it was not working when we last tested it.

 

[Perry Babin]

I got a response from SS. The schematic for the PWM circuits are not available for this amp.

If only resistors and capacitors (no diodes, no ICs, no transistors) are directly connected to pin 9, I think the IC is defective.

 

[fs1lag]

6,00V on pin 9 now is that ok? i've removed the clamps which push the transistors (or fet's whatever ;-)) towards the heatsink so i could reach the soldering point of those, both the switching fet's as the end transistors (or fet's) i've redone the soldering, because when i was measuring earlier on the 3525 ic suddenly the power came on again for a second.. i found that when i moved the mainboard a little in position towards/from the heatsink i could repeat dropping/gaining power, so i decieded those clamps had to come off, i don't how they do that at the factory but we slid them out by tapping with a little hammer, now the amplifier turns on and stays on!

unfortunately in one of my earlier attempts i've broken off the connection pins of one of the rectifiers, that's been ordered, so i hope afterwards i can enjoy my beast again

i want to thank perry for the time and effort, i'll let you know when i have the new rectifiers if all ended well

 

[Perry Babin]

Clamp removal:

http://www.diyaudio.com/forums/showthread.php?postid=1317683#post1317683

6v is high for pin 9 but at least it's producing output. While it IS working, you should measure and record the voltage on all 16 pins for reference.

 

[fs1lag]

finally the broken part came in, the amp seems to be working again.. i hope it'll last when it's back in the car!

 

[fs1lag]

well installed it in the car again yesterday, sounds as good as ever and this morning to work still all ok

one problem though while connecting i noticed one of the channel (n°4 or 3) does not produce a clear sound, there's a little cracking in it, like when the speaker is broken (which i first thought)

does anyone know what the cause may be for this issue?

 

[Perry Babin]

Dirty contacts in switches or potentiometers can cause this. Have you tried moving all of them to see if it makes a difference?

Have you tried swapping RCA signals from other channels?

Have you tried swapping the speaker wires from a working channel?

If the problem is made worse when you tap on the amp, you probably have a broken solder joint in the defective channel.

 

[fs1lag]

after a couple of months lying here i've got myself a new (other) car in which i needed it to work again, so open it went and i saw 1 little condensator 100µF which had blown when redoing all soldering in the past i accidently made a short circuit, i replaced the C and redid the soldering again of most things and now the amp is working again like it should for over a week now!

 

[fs1lag]

and for 2 months already now so it's finally repaired like it should, again thanks for the thinking along