Hey guys! I am brand new to this forum! I wanted to see if anyone would be able to help me out with a well-used Alpine 3555 car amplifier from the mid 90s. that does not power on fully - it immediately turns the Status Monitor light to orange. The amplifier was stated to work in the eBay ad when my friend bought it, but as luck would have it, it doesn't work anymore. A measured 12.6V was applied to the power and turn-on terminals, and a good ground was connected, and also I tested it with and without RCA cables connected, and also with and without speakers connected, but it always has the orange Status Monitor light. The speakers produce a thumping noise occasionally, so I am thinking the amplifier is either trying to come on, or is trying to produce sound. I opened the case and examined the board; it is surprisingly very clean, and nothing is visibly burned or missing, and no blown capacitors. Am I looking at bad output transistors, or something else? I have experience in repairing circuit boards, but no car amplifiers unfortunately. Any suggestions would be appreciated!
thanks, Jason
thanks, Jason
Hey Perry, thank you for replying back to me. I had not yet removed the circuit board from the amp chassis, but very glad you asked about LD501 and LD502, as those are screwed down in the top of the chassis under the circuit board. The LEDs are very close together inside a plastic holder, so I pulled them out to see them better during the next time I powered it up. Here is where things got interesting though, because when I flipped the circuit board over, I immediately noticed a dark spot on the board where some components had gotten very hot. The dark spot looked to be a mixture of the board itself and some carbon. The circuit board itself was slightly burned away in a few spots. I cleaned all of the char and carbon off the board and placed it back in the amp chassis. I connected all the cables to see which LEDs came on for you (both came on), and then it switched to green (both of them)! I had never seen it completely power up. I quickly grabbed a RCA cable and connected my stereo, and a speaker and all four channels produced music. After about 5 minutes of playing music though, the components over the spot on the board that had burned was very hot, like I figured they would be. The components are Q560, Q561, D559, R610, and R611. I am thinking I should replace all of these, right?
Those are transistors used as voltage regulators. You can expect them to get hot. Replacing them won't change that.
Is the board black like charcoal where it got hot?
Is the board black like charcoal where it got hot?
Hey Perry, the board was black with the charcoal like substance which I scrapped off. It was roughly about the size of a dime, and included all of the solder connections of the components in the area. I guess that stuff was causing the components to short out together? Also would you know the ratings of those resistors so I can see if they are still okay? Or do you have a schematic of that amplifier by chance?
From the photo, it appears that the bands are brown, black, brown, gold. That's a 100 ohm resistor with a ±5% tolerance.
If the board had not turned to a charcoal-like substance (carbonized), it's likely OK. I don't know if the substance that you scraped off was conductive or not but if you can find a piece of it, you can check it with a multimeter.
If the board had not turned to a charcoal-like substance (carbonized), it's likely OK. I don't know if the substance that you scraped off was conductive or not but if you can find a piece of it, you can check it with a multimeter.
Perry, I was looking at some of the other threads on this forum, and noticed this one:
http://www.diyaudio.com/forums/car-audio/201406-alpine-3553-not-turning.html
which is very similar to the problems I was having, but I noticed you had him measure the output voltage on a couple of ICs. Do you know where these are at on my amp? The 3553 component numbers seem to be different from my 3555. I would like to check the output voltages before placing this amp into service. Thank you!
http://www.diyaudio.com/forums/car-audio/201406-alpine-3553-not-turning.html
which is very similar to the problems I was having, but I noticed you had him measure the output voltage on a couple of ICs. Do you know where these are at on my amp? The 3553 component numbers seem to be different from my 3555. I would like to check the output voltages before placing this amp into service. Thank you!
The damage shown in the photo you sent me looks more like damage from leaking capacitors. You need to scrape away all of the blackened material, even if you have to scrape through to the other side of the board. Then replace the capacitors.
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