Amcron Macro-Tech 1201 with noisy channel 1

[Paulmongan]

Hi everyone,

I have a Amcron Macro-Tech 1201 on my bench with nearly same problem that was reported in another thread with a diffeeent crown amp.

In my case Ch.1 is noisy like a constant crackle like a radio. With no input. It sometimes goes away then comes back again. I get the Signal / IOC light illuminating / flickering as you would expect, but every time the light flickers, I hear a crackling distortion in the output.
I have eliminated the pots on the front panel because when I swop them over the fault is still there on Ch.1.

If I put an input into channel 1 via mixing desk with audio I have audio with next to no noise. . Just audio. If I remove the input to ch.1 and turn up volume all is ok. Now I can’t get it to replicate fault. I turn on and off. Still ok. I put it all back together and put it in the rack. And the noise is back again.

I cleaned the entire inside carefully and looked for obvious signs of disaster but can’t see anything standing out.

I swapped Ch.1 MC3307079P and LM339N ICs on main board exactly with Ch.2 side - noise still there.

I did try and do the obvious poke around with the wooden insulated stick but nothing alters the constant noise on the channel when it is noisy. And when it is quiet I can’t get it to be noisy.

I have checkled for dry joints on the main board. Found a few but did not fix the problem. I checked the large filter caps and they are very well secured to the binding lugs with Philip head screws. The cap is testing good.

So I seem to have an intermittent problem here. I’ve spent a lot of time on it but can’t seem to work out what is wrong.

I’m hopeful that someone Could maybe give me a hand to see what I could try next.

Many thanks
Paul

[sgrossklass]

This might win the stupid question of the day award, but you have cleaned the mono/stereo/BTL switch, right?

[Paulmongan]

Sgrossklass, thanks for your response. That is a good question. Yes, I did clean it. I just cleaned it again with Deoxit D5 to be sure But, the noise is still there the minute I turn up the volume on Ch1.

[sgrossklass]

Originally Posted by Paulmongan

But, the noise is still there the minute I turn up the volume on Ch1.

That pretty much narrows it down to the input section then.



My bets still are on bad contacts or solder joints in the area. Rack mounting potentially changes mechanical stress levels.

[nigelwright7557]

Originally Posted by sgrossklass

My bets still are on bad contacts or solder joints in the area. Rack mounting potentially changes mechanical stress levels.

With the pcb out of the rack twist it back and forth to see if the problem returns. Could be a cracked pcb or solder joint making intermittent contact.

On my new pcb builds I always twist the pcb back and forth, so if there are any unsoldered or cold joints they show up.

[Paulmongan]

Sgrossklass and Nigel,

Thanks for giving your advice. Yes you where right in narrowing it down to a bad connection. I eventually found it. It was a bad connection on the jack input itself. I found it by inserting a jack into the socket and by just wiggling it in place I was able to make more noise. What is strange is...that was the first thing I soldered when I started to work on it. For rework I suppose it’s nearly better to remove the solder and re solder it again rather than just touching the iron on the connection. ��

So I removed the solder completely and re soldered it again. Noise gone. Fantastic.

Again,thanks guys for responding and giving advice.

Paul

[nigelwright7557]

Originally Posted by Paulmongan

Sgrossklass and Nigel,
What is strange is...that was the first thing I soldered when I started to work on it.
Paul

If it was the first thing then maybe the iron wasn't quiet up to temperature ?
Also larger joints tend to need a bit more heat as there is more mass to warm up.
I have lost count of the number of TV SCART sockets I have had to rework for people because they came loose.

The jack socket is also prone to stress as it has lead hanging off it.