soundcraftsmen a5002

[changsecho]

hi i have a problem in the left channel in this amp i get sound but distorted.I have changed all the outputs all the resistors all the transistors in the amplifier board changed the power resistors in the power board i have done everything i can think of to get this fixed i also changed the capacitors any help surely i would be greatfull thank you

[anatech]

Hi changsecho,
Now you know what doesn't work as a repair tactic.

What was the amp doing before you changed all those parts?

Now for the questions.
Do you have a good DVM?
An oscilloscope?
Clean, well lit work area?
Another channel that works fine?

-Chris

Edit: a small question. Do you have the schematic or the servcie manual?

[changsecho]

hi thank you for your reply the left channel is distorted the right one is fine i have no service manual i would be greatfull if you could put me in the right direction where to look i don;t have all that equitment you mention thats why i changed all those parts i'm not a pro at this but i do love to try to fix them however i do know a little about amps thank you

[anatech]

Hi changsecho,
With out so much as a DVM, I can't see you completing this project. You really need this basic instrument, without which you are dead in the water.

Did you install the exact new parts, or did you use something else? If so, what did you use?

Also, appropriate capitals and some punctuation would go a long way to helping with your posts.

-Chris

[changsecho]

Hi i was in a hurry my last post yes i do have a dvm in fact 3 as far as my typeing go's lol i;m not the best.i'll try to do better.I got most of my parts at mouser i got the mj15024/25 and mostly nte transistors xicon for capacitors.Anyway my service manual the writing is so small i can;t read it.It's useless.i even changed the triac same thing distortion in the left channel.there is a carbon resistor on the ground of the speaker termal to the case it keeps toasting it maybe this will tell you something.Do you think it;s in the power supply maybe one of the filter capacitors at this point i don't have a clue. You probably think i should hang it up and take the thing in i don;t give up easy.I would like to know your views here point me in the direction where the problem is.Thank you for helping me.

[anatech]

Hi changsecho,
Reinstall the old semiconductors unless they are defective.

mj15024/25 and mostly nte transistors

The On Semi parts are okay. The NTE parts are expensive garbage, never buy those again. They need to be used for experimenting or binned.

Did you buy and use fresh thermal compound and mica insulators? If not, you must at your earliest opportunity.

Once you have the correct parts installed, we can solve your problem.

there is a carbon resistor on the ground of the speaker termal to the case it keeps toasting it maybe this will tell you something.

I suspect it's in series with a capacitor, 0.01 uF ~ 0.47 uF. If this is the case, it tells us that your amplifier is oscillating. This is a stability fault. You should check that you supply decoupling caps are okay and the solder connections on your compensation caps is okay. Use a magnifying glass to read your manual. I use reading glasses.

-Chris

[PB2]

Originally posted by changsecho
Hi i was in a hurry my last post yes i do have a dvm in fact 3 as far as my typeing go's lol i;m not the best.i'll try to do better.I got most of my parts at mouser i got the mj15024/25 and mostly nte transistors xicon for capacitors.Anyway my service manual the writing is so small i can;t read it.It's useless.i even changed the triac same thing distortion in the left channel.there is a carbon resistor on the ground of the speaker termal to the case it keeps toasting it maybe this will tell you something.Do you think it;s in the power supply maybe one of the filter capacitors at this point i don't have a clue. You probably think i should hang it up and take the thing in i don;t give up easy.I would like to know your views here point me in the direction where the problem is.Thank you for helping me.

If the resistor is from the ground to the case, then you have a large voltage between chassis ground and signal ground, check your grounding, especially screws on the chasis and large caps.

Would you be willing to scan the manual at a high res and mail it?

I happen to have one of these sitting around also in need of repair.

Pete B.

[anatech]

Hi changsecho,
May I jump on the manual bandwagon? I don't have it either. I'm sure other people will need it as time goes by. Plus it will help if we need to get into specifics on your amp.

-Chris

[PB2]

http://www.diyaudio.com/forums/showt...700#post210700

[PB2]

As I said, I have one here that was given to me for parts, I've not touched it in many years but just decided to have another look.

I do remember all the connectors, low quality connectors will corrode over time, they are often the largest contributor to failures in electronic systems. Too many in this design, IMO.

This amp worked well for several years, then blew outputs in one channel. Was repaired by the dealer, same channel blew within months. Might have been repaired one more time, blew.

One channel, the one that has held up, has 8 and 5 outputs from memory, the other has Toshiba replacements.

The transformer is huge!

Would make a nice chassis for a more reliable design. I would still like to see the repair manual for this amp.

Pete B.