Help! Famiclone sound distorted [SOLVED]

[jpx72]

I'm having trouble repairing this famiclone:
http://jpx72.detailne.sk/stuff_files/fc/famiclonefamily400.jpg
The sound after power-on is okay but after cca 5 mins it slowly becomes distorted to a level when it's almost unbearable.
Here's a taste of what I'm talking about: http://www.mediafire.com/?7g207j5hvfn6gnd
It was one of my first repairings and I replaced CPU, PPU and 2x 74 368 without any change. Yesterday I opened the thing and I want to get to the repairs again, but don't want to spend my time wasting on something that has no meaning, so I am asking anybody that had similar problems for help!

[133MHz]

That sounds weird! Have you tried pulling the sound directly from the CPU pins (1&2)? Is it still distorted?
If the sound comes out clean from the CPU then you know it's gotta be one of the passives in the audio output circuit. If it distorts right out of the CPU then the voltage regulator might be at fault - one time I had a 7805 on a Famicom that was making the +5V line noisy as it warmed up but still performed relatively OK as far as voltage stability went.
If all else fails, a can of freeze spray may help you identify the culprit.

[jpx72]

Thanks! I'm using the original sound output, I'll try to pull it out from the CPU.
The idea with a faulty 7805 is interesting, I have to try that first!!!
Post Merge: October 16, 2012, 11:32:44 am
Damn! It WAS 7805! Thanks 133!!!

[133MHz]

I'm glad you were able to fix it. There's no such ting as having too many Famiclones!
Those 7805s (especially the very cheap ones) tend to go noisy on the output as they warm up when old and marginal, causing all sorts of weird problems but still giving a correct voltage reading on your average multimeter.

[jpx72]

It is my favourite Famiclone! http://jpx72.detailne.sk/collection_files/consoles_files/famiclone/videogame400_1.jpg
This type was sold shortly after the '89 revolution on our market nationwide as an official Nintendo console together with some quality pirate multicarts (the violet colour ones). I have seen real NES on the internet some 10 years later, and Famicom even later! I remember paying 2500Sk for my first one which in that time was nearly 1/3 of my father's monthly salary
It's funny that the store exists till this day, but today, they will be prosecuted for selling such chinese uncertified consoles!

Recently I have been watching the awesome "Russian Dendy chronicles" on youtube, it reminds me strongly of my country's story Although we haven't got the problem with black and white SECAM vs. PAL (cause we already had PAL), many of my friends back then had only black and white TVs so the result was the same It's only a shame that we didn't have "our" famiclone company like the Russian Dendy, or Pegasus in Poland.

But back to the topic, yesterday I left the console running with the new 7805 for one hour and the sound was clear for the whole time. So the problem is solved. But I found another problem with missing extra sound chanels from the cartridge's external sound chip so I traced the sound line from CPU and found out that it was entering pin 46 of the cartridge and outputing sound from pin 45. So completely obversely (should be entering 45 and outputing from 46). These pins were even connected together on board by default.  So it took one three cuts and two wires to make the Gimmick go funky!