Alpine 3552 damaged power circuitry - diyAudio
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Old 27th March 2009, 04:14 AM   #1
Kei is offline Kei  Wales
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Question Alpine 3552 damaged power circuitry

I have just signed up here as it seems to have quite a vast base of knowledgeable people on the subject of repairing amplifiers that have malfunctioned. (i have searched but to no avail)

I have been given an Alpine 3552 four channel amp by my dad, and i have subsequently found that 3 of the transistors have completely burned out.

Click the image to open in full size.
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My dad claims that the amplifier was working when he removed it from his car 10 years ago, it hasn't been used since. I haven't tried powering it, as i don't want to make matters worse. I have had a look and i can get the exact same transistors to replace the dead ones(Sanyo D1669), but i don't have a clue what caused this to occur and therefore don't want to buy and fit replacements and have this happen again. (Each transistor is 1.45) I know that the amp has never been abused, as my dad was never like that, but if anyone has any ideas as to a possible cause i would greatly appreciate any help.

Btw, if anyone has the service manual/schematics/circuit diagram for this amp the 3554 or similar it would be very useful. (i already have the owners manual)

Thanks.

Last edited by Kei; 15th January 2012 at 09:07 PM.
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Old 27th March 2009, 04:53 AM   #2
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Shorted output transistors are the most common cause of a blown power supply. You'll need to check them before replacing the power supply transistors. You should replace all 6 of the 2SD1669s. If the others haven't failed, they could be damaged.

It also appears that some of the resistors have burned. If I'm not mistaken, the ones in series with the base of the transistors are 1 ohm and the ones from the base to ground are 10 ohms. Confirm by looking at the values of the ones for the transistors that did not burn.

If you insert a 15 amp fuse in the B+ line and have all transistors clamped to the heatsink when you apply power (after replacing the defective parts), it should protect the new parts from being damaged.
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Old 29th March 2009, 09:45 PM   #3
Kei is offline Kei  Wales
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Thanks for the reply Perry, i will be looking into it this week.

The resistors do indeed appear to be 1ohm and 10ohms (5% tolerance). Do you know what power rating these resistors are? (The knowledgeable one in my house is not being particularly forthcoming with any information , and he wants me to find him a circuit diagram for the sm-ps or one that is very similar) Anyway, do you think the Sanken 2sc3852 also need replacing, if so do you know an equivalent part, as i cant seem to find one.

Same story for the output transistors, which are also Sanken 2sC4386 & 2sA1671. I am assuming that if one is shorted, it will need to be replaced. I have managed to google some equivalent part numbers but when i have looked for a supplier i still cant turn up any results.

And last of all just to keep the old one happy do you have any service manuals for any alpine amplifiers of similar vintage? (it'll stop the nagging in my ear )

Thankyou.
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Old 29th March 2009, 10:01 PM   #4
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The resistors are probably rated at 1 watt.

I don't remember any failing but it's been a long time since I worked on any of these amps.
http://octopart.com/search?q=2sc3852

Determine if you have shorted outputs. If you do, then we can try to find replacements.

I have the 3550 manual. The supply is similar (same basic circuit but different values for many components). Email me if you want it.

babin_perry@yahoo.com
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Old 5th April 2009, 11:21 PM   #5
Kei is offline Kei  Wales
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Default Tested Transistors

I have finally made some progress and tested all of the main transistors in this amp. The good news is that only the three 2sc1669 transistors that got heavily burned are dead, all the others appear to be functional. The bad news is that this makes finding out what caused this fault to occur more difficult.

Since it appears that all of the output transistors are perfectly functional, along with the rest in the switch mode supply, does anyone have any ideas of what else to search for? (Before i replace the knackered bits and power it up)

Also, i thought it odd when i took it apart that there were no micas between the transistors and the heatsink, only the standard white thermal paste, is this normal? (The service manual Perry sent me shows that there should be micas under all of the transistors)
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Old 5th April 2009, 11:30 PM   #6
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The fully encapsulated transistors don't need (shouldn't have) insulators. In most instances, when the fully encapsulated semiconductors are used, heatsink compound is the only thing between the semiconductors and the heatsink.

Sometimes power supplies fail and there are no other problems. If the outputs are OK, it's possible that the transformer is shorted. It's also possible that this is one of those times that the power supply fails randomly. Amplifiers this old will begin to have random component failures.

When you power it up, do so through a 15 amp fuse or some type of current limiter. Clamp all semiconductors to the heatsink before applying power.
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Old 6th April 2009, 04:40 AM   #7
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I have a 3555 here I just tested and one channel has rail voltage, yet the outputs test good. There is high voltage on the base of that output holding it open (or it is leaking). Not investigated more, but is possible something like that could blow the PS if the amp were hooked up. If it starts up ok after your repairs then test voltage on all speaker terminals before you hook any speakers to it. There should be very little, like only some millivolts DC.
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Old 18th May 2009, 08:21 PM   #8
Kei is offline Kei  Wales
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Appologies for not replying for so long, i have been occupied with alot of university work.

I have accumulated all of the parts that i require to rebuild the 3552, which i will be doing during this week, and obviously when i come to test it i will tryout most of the suggestions above.

Unfortunately to give me a spare amp just in case the 3552 blew-up again, i purchased an Alpine MRV-F400 and to my misfortune the same problem occured when i hooked it up to test it. Initially it came on ok but the output to the speakers was basically white-noise, which lasted all of a minute before the ruddy thing went pop which roasted one of the FET's (IRFZ44), and damaged the traces on a grounding post. At least i still have one good amplifier, even though i now have two dead ones.

I am now looking for a schematic for this amp, I believe that you may have one Perry. (Low resolution copy i saw in another thread) If you do i will send you another e-mail.
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Old 19th May 2009, 08:07 PM   #9
Kei is offline Kei  Wales
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Here is an image showing what is damaged on the V12. It seems that the grounding strap for the Fet heatsink suffered the most here, plus the missing fet that got roasted.
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Old 19th May 2009, 09:36 PM   #10
jol50 is offline jol50  United States
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People short the case or have a bad ground and trash a lot of those case grounds. That looks good to me, I just had to beef up a pad on one that got so hot it let loose at the edge. I ran wire to all of them to hold it better, though the clamps are quite good in those.
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