I just got a Sundown amp in that goes into protect the second remote turn on voltage is applied. There does not appear to be any shorted outputs or ps fets either visually or testing with the meter. All fuses are intact as well. The previous owner claimed it was working fine and then just went into protect one day and obviously never came out. Voltages on the TL494 are as follows
1. 6.5 V
2. 4.5 V
3. 4.5 V
4. 0.2 V
5. 1.3 V
6. 3.4 V
7. 0.0 V
8. 13.7 V
9. 0.0 V
10. 0.0 v
11. 13.7 V
12. 13.6 V
13. 4.8 V
14. 4.8 V
15. 4.7 V
16. 0.0 V
I think something is driving pin 1 high.What are some typical things that cause this issue in this or similiar amps?
1. 6.5 V
2. 4.5 V
3. 4.5 V
4. 0.2 V
5. 1.3 V
6. 3.4 V
7. 0.0 V
8. 13.7 V
9. 0.0 V
10. 0.0 v
11. 13.7 V
12. 13.6 V
13. 4.8 V
14. 4.8 V
15. 4.7 V
16. 0.0 V
I think something is driving pin 1 high.What are some typical things that cause this issue in this or similiar amps?
There is an lm393 which appears to be a similiar part. It isnt near the 494 but there is at least one trace connecting them. I didnt get anything as far as voltages yet but i did find a shorted 15v zener connected to the vcc pin of the lm393. I havent got the chance to replace it yet. Hopefully I will have a chance to tear back into this when I get home.
Well the shorted zener was a false alarm. My leads were shorting on a small buss bar. The only voltage I am seeing on the lm393 is on pins 1 and 8. Using the ground pin as reference the voltage slowly climbs to about .2 volts on both pins when power is applied but then it starts to go down and swings negative.
Is this a reflection on the caps or are they blown ??
An externally hosted image should be here but it was not working when we last tested it.
Just the flash playing tricks. The caps are not bulging by any means. I finally got some time to poke around in this amp a bit. I found 4 of the 12 PS FETS with intermittent solder connections so I went ahead and resoldered them all. The pins connecting the driver board to the main board looked as if they had seen some heat so I resoldered all of those as well hoping that might solve the issue but the amp still would not turn on. I am dreading having to pull that driver board to work on it as the whole thing is encased in black epoxy. I hope the problem is anywhere else but after seeing the solder connections going to that driver board I just have a feeling it is in there somewhere.
I pulled all the outputs tonight and I did not find any defective parts. All measured as they should. I powered the amp up without the outputs installed for the heck of it and still the amp went straight into protect. I reinstalled the outputs and then removed the driver board and tried again to power it up but again it went straight into protect. If the driver board is bad I don't see any way of repairing any defective parts on the board without destroying it in the process. It is almost completely encased in a very solid epoxy. I am running out of places to look on this thing. Next and maybe my last shot is to start pulling and checking the small transistors in the turn on circuit to maybe see if there is any fault there. I may just end up sending this one to db-r unless them or sundown would be willing to sell me a driver board only.
Got a hold of chris and he said 90 dollars flat rate which seems reasonable. I will probably send it on to him as I haven't had much time for amp repair lately anyways and I'd like to try this thing out in my car when the weather gets nicer . Hopefully he will let me know exactly what he finds. I'm gonna kick myself if its not the driver board.
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