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:

and reworked power connector using an adapter which I did immediately cross:

"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.

[Advertiser]

[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.

[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.

[Gelip]

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

- original PSU (modded MOLEX) - cracks

- AT PSU - no cracks. Before at this PSU have cracks - not understand Byte working good, no cracks. Very strange.


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) . 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
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

[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
Probably DD75 is also good. This cracks have other source

[Tronix]

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