Altec Lansing IM7 IRF7379 Amp Problems

[MotorMouth93]

Hi everyone!

I was given an Altec Lancing inMotion IM7 a while back and I shorted the subwoofer amplifier accidentally trying to mod it. One of the IRF7379 chips caught fire and burned up two small parts near it.

The IRF7379 I replaced:



The two smaller parts: (One of them says "KA2" and the other says "Z 2")



So far what I have done:

1) I replaced the IRF7379 that burned up. (Amp worked but had crackling noises)

2) I removed the two smaller parts and replaced them with others from another channel's amp, sound improved but horribly distorted at high volumes.

3) Removed the two replacements, put them back where they came from, and left the solder pads empty. No crackling but horribly distorted at high volumes.

^This is where its at now. What are the two little parts and where can I find them? Ive looked all over and don't have a clue. Also, what else could be wrong and causing the distortion?

Thanks in advance! If its totally screwed I guess I'll just have to buy a shiny new IMT810 haha.

[nigelwright7557]

They look like transistors.

You could do with a circuit digram so you can fault find sensibly.

[MotorMouth93]

I've done a lot of googling and I can't find any schematics for this amp board. Does anyone have any ideas of what could cause the distortion?

[AudioAudio]

Originally Posted by MotorMouth93

I've done a lot of googling and I can't find any schematics for this amp board. Does anyone have any ideas of what could cause the distortion?

Have you made any progress on this? I have an IM7 with a similar issue. I ran it at high volume for several hours last summer and it was great. Next time I turned it on, all I got was a loud bass thump and no audio.

I tried it a few months later and now it works again but easily distorts at volumes just above background level. The EQ seems to be a contributing factor as despite the ability to still adjust them with the remote, the sound is overly bright and too bass-y.

Thanks for those photos. I haven't opened mine yet - are there any pitfalls and suggestions about what might be wrong?

[Baldin]

The smaller parts are marked D20 and D21 ... these are diodes. I would guess these together with the two resistors between R103 and R10x (cant see the last digit) form the gate input circuit. Seems that the two diodes are the same (make sense) marked KA2 .... Try to google for this markin ... would think it's some kind of 1N4148 ... Vishay maybe ....

Cant read the marking on the bigger chip (U28) behind the big cap ... it's probably the driver/class-d modulator ... can you state it here?

Best regards Baldin

[Baldin]

Diodes:
http://www.diodes.com/datasheets/ds12003.pdf
but any MMDB4148 or IMDB4148 would brobably do .... you can also just try a 1N4148 leaded first if you can fit it ... change both diodes