A friend gave me a 2x200W audio amplifier composed of 2 PCBs (providing 200W each), which keeps blowing inner fuses.
I don't find any documentation related to this amplifier (Pro System PS400): The PCBs aren't named and the brand doesn't seems to be very popular.
He bay this amplifier to a flea market so the previous owner is not reachable to be asked questions.
There are 4 fuses sockets for main DC voltages (corresponding to +40VDC and -40VDC supply voltages for each card).
When I dissembled the case for the first time, I notice 4x F3.15A 250V fuses placed on their sockets. However, I'm not 100% sure these fuses are the original ones (maybe the previous owner tried to change the fuses and chose a wrong reference?)
I verified the following things:
1. I retried by replacing F3.15A by a slow type T3.15A 250V fuses: FAIL.
2. Transformer: Secondary winding disconnected from the PCBs: 230VAC (France) -> 30VAC measured [marked 220VAC (formerly in France) -> 27VAC].
3. DC voltage: ±40VDC after the diode bridge (while the 2200µF capacitors are only 35V DC rated!)
I desoldered one of these capacitors (4 in total) and tested it: the charge/discharge curves are OK.
Conclusion: The AC/DC conversion seems to be fine although I'm surprised the capacitor 35V DC rating is exceeded.
To prevent fuses from blowing, I used a light bulb current limiter (75W light bulb). The light bulb brights immediately after I switched on the amp.
I performed this test on both cards (only one card connected at a time) and it appears that the short circuit problem seems to be the same on both cards while they are independent. I didn't see any hard short circuit on both PCBs.
What tests could I do to isolate the fault?
I don't find any documentation related to this amplifier (Pro System PS400): The PCBs aren't named and the brand doesn't seems to be very popular.
He bay this amplifier to a flea market so the previous owner is not reachable to be asked questions.
There are 4 fuses sockets for main DC voltages (corresponding to +40VDC and -40VDC supply voltages for each card).
When I dissembled the case for the first time, I notice 4x F3.15A 250V fuses placed on their sockets. However, I'm not 100% sure these fuses are the original ones (maybe the previous owner tried to change the fuses and chose a wrong reference?)
I verified the following things:
1. I retried by replacing F3.15A by a slow type T3.15A 250V fuses: FAIL.
2. Transformer: Secondary winding disconnected from the PCBs: 230VAC (France) -> 30VAC measured [marked 220VAC (formerly in France) -> 27VAC].
3. DC voltage: ±40VDC after the diode bridge (while the 2200µF capacitors are only 35V DC rated!)
I desoldered one of these capacitors (4 in total) and tested it: the charge/discharge curves are OK.
Conclusion: The AC/DC conversion seems to be fine although I'm surprised the capacitor 35V DC rating is exceeded.
To prevent fuses from blowing, I used a light bulb current limiter (75W light bulb). The light bulb brights immediately after I switched on the amp.
I performed this test on both cards (only one card connected at a time) and it appears that the short circuit problem seems to be the same on both cards while they are independent. I didn't see any hard short circuit on both PCBs.
What tests could I do to isolate the fault?
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