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

[Gelip]

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/9115329900_1381147993_thumb.jpg (http://obrazki.elektroda.pl/9115329900_1381147993.png) http://obrazki.elektroda.pl/9055716500_1381147993_thumb.jpg (http://obrazki.elektroda.pl/9055716500_1381147993.png) http://obrazki.elektroda.pl/7804442200_1381147994_thumb.jpg (http://obrazki.elektroda.pl/7804442200_1381147994.png)
and reworked power connector using an adapter which I did immediately cross:
http://obrazki.elektroda.pl/3333862700_1381148219_thumb.jpg (http://obrazki.elektroda.pl/3333862700_1381148219.png) http://obrazki.elektroda.pl/6667791900_1381148219_thumb.jpg (http://obrazki.elektroda.pl/6667791900_1381148219.png)
"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.

[HardWareMan]

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

[Gelip]

Interference on the input of the amplifier through the power rail. Need to unleash the power of analog and digital parts.
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/3890003.htm) http://savepic.net/3883859m.png (http://savepic.net/3883859.htm)

[HardWareMan]

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 (http://www.nedopc.org/forum/index.php).

[Gelip]

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

- original PSU (modded MOLEX) - cracks
http://speccy.pl/forum/index.php?action=dlattach;topic=1155.0;attach=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?action=dlattach;topic=1155.0;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 :)

[HardWareMan]

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

[Gelip]

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

[Gelip]

"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 (http://www.youtube.com/watch?v=_uZha2SGwa0)

[Gelip]

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::(

[Tronix]

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

[Gelip]

... and give sound signal before amplifer (from "minus" C14).
Sorry, not understand. Please clearly and maybe draw scheme please.

[Tronix]

http://habrastorage.org/files/b58/421/4a8/b584214a87154ae49fa3bed2b8438952.png

[Gelip]

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

[Tronix]

Yes

[Gelip]

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

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/4751712.htm) http://savepic.net/4744544m.png (http://savepic.net/4744544.htm)

[Gelip]

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