Alpine 3553 not turning on

[Dr Zeus]

Alpine 3553 looks very much like the 3552 on the DVD, only this one has an input/xover daughter board, plus each channel output pair has its own individual thermistor like I have not seen on any amp before.

This amp appears to ave a failed power supply with all 2SD1669s shorted from legs 1-3. (Measuring exactly 4.3 ohms on all 6)

I carefully lifte all 1&3 legs off all PS transistors and to my surprise they actually measure OK. From pads 1 to 3, I still measure 4.3 ohms.

What gives?

The amp will not power up and does not draw anything.

 

[1moreamp]

Your reading those 1/2 watt resistors right in front of the 2Sd1669's. If the 1669's are ok I would look for a open trace, or a bad turn on transistor in the supply....🙂

 

[Dr Zeus]

OK i found a bad trace to ground. Amp tried to power up but fails.

TL494
Pin 1: 0.002
Pin 2: 4.98
Pin 3: 0.089
Pin 4: 4.96
Pin 5: 1.663
Pin 6: 3.666
Pin 7: 0.001
Pin 8: 13.75
Pin 9: 0.001
Pin 10: 0.001
Pin 11: 13.75
Pin 12: 13.75
Pin 13: 4.99
Pin 14: 4.99
Pin 15: 4.99
Pin 16: 0.001

The amp is pulsing slightly every 6~7 seconds. During which, all 4 channels appear to have some DC voltage across them. Voltage numbers on the TL494 dont change very much.

 

[Perry Babin]

Find the PNP transistor with it's collector connected to pin 4 and remove it. That should disable the protection circuit (so be careful) to allow you to see if there is a problem with one of the channels.

 

[Dr Zeus]

Cool I was looking for something like that last night. I bleieve that is Q525 to be pulled. I'll work on it tonight.

Thanks

 

[Dr Zeus]

Removed Q518. Amp powers up. +-26v rail. it appears there is no negative regulated voltage on the opAmps.

IC404
Pin 1: 13
Pin 2: 2.9
Pin 3: .25
Pin 4: .9
Pin 5: .25
Pin 6: 2.9
Pin 7: 13
Pin 8: 13

After about 5 minutes of power-on time, the ps and outputs start to get pretty warm.

I believe I just found an open/burned 1/8w resister R528 and a 1/2w R530 next to the negative voltage regulator, Q514

 

[Dr Zeus]

I also found a 25v 100uF cap leaked nearby to this regulator - It probably shorted and blew open, which in turn took out the above resistors.

Upon replacing all three pieces, plus re-installing Q518, the amp powers and plays across all 4 channels.

Thanks perry!

 

[Dr Zeus]

Upon assembly, I also remember the following on this amp; Cold solder on one of the torroid legs, and cold solder on one of the rail busbars.