ฝัง
- เผยแพร่เมื่อ 21 ส.ค. 2024
- In this JAKAREPAIRS episode I show how to repair a dead Amphion Impact 400 subwoofer. The same amplifier is used in Bolzano Villetri BG SUBWOOFER, TruAudio TC-12 Subwoofer and probably some others as well.
UPDATE 28.2.2016:
I got the subwoofer back for more repair. It was too silent even at maximum volume. I tracked the problem to a 4.7 µF capacitor at main amp board. With new capacitor, volume was OK but there was some buzzing noise for about 15 seconds after turning the subwoofer on, which slowly disappeared. Also, when listened with higher volume setting, it made a clanking sound every now and then, which sounded a lot like that the element was bottoming out but it wasn't. I ended up replacing all the electrolytic capacitors from both the main amp board and the crossover board, total of 26 capacitors. About 30 % of those were totally dead! I only left the two big 4700 µF capacitors as they were OK and also left all the NP (non-polar) capacitors since those were not easily available. Now all the buzzing and clanking is gone, the subwoofer works like a charm. I would have saved a lot of time if I would just changed all the capacitors in the first place and not hunt which one is broken!
Thanks for good video. I had the same problem and it was very easy to repair. You did very big job to find out how the circuit works.
Good to hear you got it working.
Hello. I have an Amphion impact 400 sub, and the amp just broke. Some SMD resistors just blown up(burned at all, I need their values). Some transistors and diodes burned as well. Maybe capacitors should be replaced too. Do you have some schematics or some pics with their values please? I just can't find anywhere :(. I tried to see values of SMD resistors in video, but i just can't read them. Thank you in advice!
Unfortunately I don't have the schematics, they would have also helped me a lot while repairing the amp. My friend offered a few weeks ago that I could have the subwoofer because he doesn't need it anymore. I will ask him if he still has it. Then I could look for the resistor values.
Are the burnt resistors on the main amp board or on the smaller board?
On main amp board most, but i believe on small board too, some are missing from factory i see. Some good pics would be great for comparison who`s missing by blowing and from factory, if it is possible. Ty so much :)
Thanks for a great and informative video! I do not mind the rally English ;)
I have the same sub and same problem.
Replaced a bunch of bad small electrolytics, all were bad but same problem still exists. Replaced 8 pin board with upc1237, still same problem.
If I inject like 2.6V at pin 7 then relay is energized.
There is almost no voltage at pin 7, over 3V at pin 8. Connecting pin 7 and 8 together makes voltage go very low on pin8 too.
What am I missing? Anyone have the schematic of the power amp board?
If anyone can help me I would be very grateful!
Hi Jonas,
Unfortunately I don't have the schematic diagram of the power amp. But I have marked on the schematic of the 8-pin board which I drew that there is a resistor between pins 7 and 8 and a capacitor from pin 7 to ground. See kair.us/misc/uPC1237_replacement_circuit.jpg
So I suggest to double check the capacitor at pin 7. It can be leaking current to ground and not allowing voltage on pin 7 to rise.
Also note that at least in the replacement circuit there is no input current limiting to pin 7, so use a series resistor when injecting voltage to pin 7.
I don't have experience on a real upc1237, but it could be that if some of the protections are active, the voltage on pin 7 could be pulled down. So check at least that pins 1 and 2 have 0 volts at them. Better to use a scope, as there can be ripple not seen with a multimeter. For debugging you could always disconnect the pins 1 and 2 to see if it helps, but be sure to disconnect speaker first in case there really is DC offset which would destroy the element.
And finally, there is a capacitor at pin 3 which means that the protection functions are latched. So there could be some DC offset when powering on the amplifier, causing the protection to trip and stay on, even though the DC offset would settle after startup. The latching can be disabled by grounding pin 3.
Hi,
Thanks for your reply.
No there is no real DC offset, that was the first thing I checked :)
Also now I tried grounding pins 1 and 2 and no change.
From you schematic I see that pin 8 has limited voltage due to a zener, but I had a current limit of like 30mA on my power supply so I did not damage anything with it.
Interesting that pin 7 has like at least 4 diodes of voltage drop to ground, it should not be that low then.
I checked the resistors around pins 7 and 8 and also replaced the crappy cap between pin 7 and gnd.
I will double check the cap for leakage tomorrow :)
Removed cap from pin7 to gnd. No change. Cap is a new BC, so it is good.
But if I connect pins 7 and 8 together and mains voltage is above 215VAC then relay in energized. Below 215VAC not. That is too little of a margin anyway.
50V over the 10kohm resistor is also quite much. It is like 250mW of losses...would else be tempting to swap it out for a 8k2 resistor :)
Strange. Without internal diagram of real upc1237 it hard to tell what is going on. Your replacement upc1237 could already be broken or off-spec before you installed it. What about that pin 4, is there now proper DC level?
If it works with 7 and 8 shorted, maybe use that solution for some time. If it gets again worse after some time, maybe there are more bad caps.
Pin 4! That is right. There should be like 800mV instead of 0mV. Pin4
goes directly to the crossover board and something there is wrong. I
already replaced all the small electrolytics, but it did not help.
Without a schematic I do not fully understand the crossover board. Let's
see, I will keep struggling :)