Cracks in sound speaker and MIC socket in ZX clone "Byte-48"

For some time now I have noticed that some noise in the speaker ZX Spectrum clone "Byte-48", which is also the output MIC. They appear randomly, sometimes almost absent and time intensive. I made a few modifications in the truth but I checked the power meter and there are no faults - everything is done carefully. Moreover, these disturbances were already before reworking power. Reworked a bit RGB interface by changing the function of a pin - sound output is 5V you need to switch TV in RGB mode:
http://obrazki.elektroda.pl/91153299...7993_thumb.jpg http://obrazki.elektroda.pl/90557165...7993_thumb.jpg http://obrazki.elektroda.pl/78044422...7994_thumb.jpg
and reworked power connector using an adapter which I did immediately cross:
http://obrazki.elektroda.pl/33338627...8219_thumb.jpg http://obrazki.elektroda.pl/66677919...8219_thumb.jpg
"Byte" is working normally but the interference bug me. I did it to a file Cracks.zip (MP3) - the best headphones to listen to the audio program. What could be causing this? At first I suspected power but the same thing happens on the original as well as other AT.

Interference on the input of the amplifier through the power rail. Need to unleash the power of analog and digital parts.

Цитата:

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Сообщение от HardWareMan

Interference on the input of the amplifier through the power rail. Need to unleash the power of analog and digital parts.

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You could write something more about it.

For now I want to replace all capacitors. Waiting for shipment. Most of them are scorched. The worst look C14, C13 i C11. This caps is in section SOUND, TAPE at scheme.
http://savepic.net/3890003m.png http://savepic.net/3883859m.png

You're right. C11 is most important one. You should just replace all lits, marked as "K50-6". If you want more advices you always can come to another forum.

Before replacing the capacitors decided to once again check out some PSU:

- original PSU (modded MOLEX) - cracks
http://speccy.pl/forum/index.php?act...ach=1953;image
- AT PSU - no cracks. Before at this PSU have cracks - not understand :confused: Byte working good, no cracks. Very strange.
http://speccy.pl/forum/index.php?act....0;attach=1950

Probably something is bad with my original PSU or my MOLEX mod in this PSU - maybe MOLEX plug is too loose.

For now, do not change the capacitors - see the "Byte" will work :)

Poor contact in the socket power supply generates a large ripple, which goes to amplifier input.

I test the computer already three days and all OK - no replacement capacitors :-). PSU: old AT

"Byte" acted by some days well. Yesterday load time various demos and programs, and it was OK. Today I have included computer and again Interference (PSU AT) :dizzy_mad_old::mad::(. Somehow I do not believe that it might be the fault of a loose connector MOLEX - after the normal power plug on the PC hard drive - one of the basic components of the system and very often I plug in the PC various hard drives, CD-ROMs, etc. and nothing going wrong during the operation of the PC.
There is no short circuit. I checked again carefully measure. If you would corrupt a system (amplifier) for "Byte" how is it possible that it worked well for some days! Normally I have some circuses with these disturbances :v2_dizzy_facepalm:
I will try to replace the capacitors but probably this will not help. I recorded the video. The rattling noise is heard best at the end cutscene (0:40). Listen with headphones: YouTube

Replaced all capacitors 47uF 16V, desolder transistors VT5 & VT6 and check with multimeter - transistors OK (NPN & PNP) then solder them back.
Now desolder DD75 amplifier and test "Byte" - without amp, build-in speaker not working.
Still have cracks in external amplifier (SONY tape recorder) after connect MF "Byte" to MIC (Sony) if increase volume about MAX range.
http://www.youtube.com/watch?v=OO2xqPiUEfs
http://www.youtube.com/watch?v=7H3dpTlbUjs
I test original PSU and AT PSU - with both have cracks :dizzy_mad_old:
Probably DD75 is also good. This cracks have other source :confused::(

Try desolder C14 and give sound signal before amplifer (from "minus" C14).

Цитата:

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Сообщение от Tronix

... and give sound signal before amplifer (from "minus" C14).

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Sorry, not understand. Please clearly and maybe draw scheme please.

http://habrastorage.org/files/b58/42...d2b8438952.png

OK, like this - but ground from where?
http://savepic.net/4781348m.png

Yes

OK, make connect like this but still cracks :-( (DD75 and C14 is desolder)
http://savepic.net/4742468m.png

Now desolder all: amp DD75, transistors VT5 & VT6, capacitor C14 and test computer only with 5V power supply. "Byte" working without 12V but still have cracks in external amp SONY :confused_std:
http://savepic.net/4751712m.png http://savepic.net/4744544m.png

Next i test like this:
1. Desolder R64 (SOUND) - still cracks (no BEEP sound)
2. Desolder R65 (TAPEOUT) - still cracks (no SAVE sound)
3. Desolder R46, R47, R48 (FX0, VI53) - I think something better but after some time some cracks back (VI53 not working)

4. Solder back R64 - I think there is no cracks
5. Solder back R65 - I think there is no cracks
6. Desolder sound cable C14 pin and GND
7. Solder back C14 capacitor, VT5, VT6 and DD75 amp
(not tested with desoldered R78 KDB_SND)

Now test "Byte" with AT PSU 5V + 12V (normal power supply) and no cracks (VI53 disconnect) :-) but I don't think that the VI53 is broken because Lambada last time worked.

Cracks again appears but sometimes immediatelly after power on, sometimes until few minutes - appears randomly :confused: Now, after placing everything back (DD75 amp, VT5, VT6, C14, all resistors) is sometimes something as in the video: http://www.youtube.com/watch?v=EJoyxCCKA0I