pictures of my soundstream amp

bluiezaccord

Member
2008-03-30 12:37 am
Recap, the amp works but does not shut off when the key is out. It also makes a weird high pitch noise coming from inside the amp. I checked the ground, remote, all the wires. When I took out the RCA wire from the amp, it finally shuts off. This started happening ever since I had the subwoofers wired down to 0.5 ohm. I accidentally wired them wrong. I wanted it 2 ohm. So i took out the amp and opened it. Here is how it looks.. somebody please help me. Thank you.


When I opened it, I only saw the one of the transistor was burnt, and another one had one of the three leg broken....
And when I flipped it around... it looked horrible..

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One FET has obviously failed. It's likely that all of the others in that supply (the amp has 2 power supplies -- 8 FETs/supply) have failed also. Measure the resistance from leg 1 to the other two legs of the individual FETs in the supply. If any read near 0 ohms, they (or some in parallel) are defective.

Generally, when the power supply fails, it's because the output transistors (on the other side of the amp) have failed. Check them before powering the amp up again.

You need to clamp the transistors to the sink before powering it up again.

Which transistor had a broken leg?

What looked 'horrible'?
 

jol50

Member
2007-11-08 2:14 am
The large solders on the back may look that way because they have flux on them. Often they add solder to the large joints by hand or something, you can see they were done not like the rest of the board. Make sure they did not contact the case of the amp. They need a gob of solder on them to hold the heavy component without breaking. I'd say remove all parallel transistors and replace, check or replace resistors for them and it might be fine after some testing. Post a close-up photo of the large solders on the back of the board if you can, hard to see in that photo.
 
I Tried to add more solder to them. I checked and they have these black square stubs so that it would not touch the case of the amp. I was wondering if I can use transistors or resistors from my other amps that I am not using. If so, how would I know which one to use? Thanks for all the help guys. I really appreciate it.

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Those connections look OK. It appears that someone (maybe soundstream) resoldered all of the connection. Normally, there isn't that much solder.

I knew they were there because I've spent hundreds of hours working on amps using these driver boards. This is one of several clones used by Power Acoustic and Planet audio (among others). The connections overheat on those transistors. Eventually, the solder becomes oxidized so badly that there is no longer a good connection between the board and the transistor. One transistor often loses contact first and then the other transistor is left to handle the entire load. Then that transistor fails.

The outputs are a group of 10 transistors (likely IRFB31N20Ds). The power supply FETs are a group of 16 transistors (they use IRFZ44s or IRFZ46s - Z46s are found in the later products).
 

jol50

Member
2007-11-08 2:14 am
The other numbers are usually date codes, the ones you put in new should all be the same so they are balanced (bought in a set). You may find the new parts have another letter denoting lead free. Be careful if you get them on ebay or not from a reputable dealer as there are fakes out there. Most parts like the IRFZ are not costly, there are a few you have to shop up a good price on though. btw It really should be Perry 'Guru' Babin for amps....;) He has quite a site on the subject check it out.
 
Digikey.com part numbers:

IRFZ44NPBF-ND
IRFB31N20DPBF-ND

Order by phone and tell the salesman that you need matching date codes for each part number. If they won't guarantee matching date codes, you need to order in multiples of 5. Since the packs of 5 (pre-packaged) will generally have matching date codes, that should guarantee you enough matching transistors for each group.

The other numbers are production/date codes. For each part number, they need to match for the best reliability. If you get mixed date codes, use the matched ones grouped together. The outputs are in 2 groups of 5. The power supply transistors are in 4 groups of 4.
 

jol50

Member
2007-11-08 2:14 am
The best thing to do is make sure all the transistors are matched, because if one runs harder/hotter it will blow and take out the rest. That is also why the gate resistors are often replaced too, they throttle them and cost nothing to buy. If a transistor goes bad it can short back into the resistor and damage it or they could be out of spec anyway. If everything runs equally you will get the max out of all of them instead of one blowing and spoiling your fun. That is the best way to make the amp durable/powerful as it was intended to be. Actually adding power would be very complicated, require design and testing of many variables depending on the amp. The way things are today it would be much cheaper/faster to just buy a larger amp anyway unless you like blowing and fixing amps, but some people do.:)

Also be careful in assembly; make sure the sink is clean and perfect smooth. Make sure they all lay flat without a spec of dirt under them, and have proper grease or good condition of whatever insulation the transistors are using so they get max heat dissipation. Ensure clamps are straight/tight/flat/etc. If you are going to beat the amp hard all that stuff will matter.

Last time I ordered 44s from mouser they came in a sleeve/tube all the same code. I ordered ~30 at a time. Once they back ordered, then I got a few and rest later that were different but could have changed order. I now test with those few.