Vef Sigma 260 1982. No sound .

[Gabriel07]

Hello everyone, so I am 14 don't know much about electronics and I have Vef Sigma 260 '82 year made. My problem with this radio is that I hear no sound from some channels (from 52, 49, 31, 25, CB1, and CB2) from others I hear just hissing. At maximum volume, there is very little sound coming from the speaker, but it's just hissing, no human voice or something more.
So from what can I start to search for problems?

And one more question, when you open the back cover, there is a roll above. I saw that it has little metal plates, which when turning connects to other plates. And on every channel roll late there are two plastic screws on each one. What do they do?

 

[AngelB]

Can you upload photos?

 

[Harald Kapp]

Does the cassette player work? This would exclude the audio section and diagnosis would have to concentrate on the RF section.
If there is no sound from cassette either, the defect is located in the audio section.

 

[Gabriel07]

Does the cassette player work? This would exclude the audio section and diagnosis would have to concentrate on the RF section.
If there is no sound from cassette either, the defect is located in the audio section.

I don't have any cassetes, so I can't check the cassetes player.

 

[Gabriel07]

Can you upload photos?

Which part of radio photos you need ?

 

[Gabriel07]

Does the cassette player work? This would exclude the audio section and diagnosis would have to concentrate on the RF section.
If there is no sound from cassette either, the defect is located in the audio section.

But player works, I mean when you push buttons above, that little rolls spins.

 

[Harald Kapp]

But player works, I mean when you push buttons above, that little rolls spins.

That doesn't tell us whether the amplifier section works. Try to get a cassette for testing.
Or does the radio have an aux input? Then try this input to check the audio amplifier section.

 

[bertus]

Hello,

Here is a PDF with the schematic:
https://www.docdroid.net/b8DsfsE/vef-sigma-260-prezentare-pdf
Unfortunately the text is in russian.

Bertus

 

[Gabriel07]

Hello,

Here is a PDF with the schematic:
https://www.docdroid.net/b8DsfsE/vef-sigma-260-prezentare-pdf
Unfortunately the text is in russian.

Bertus

It won't be a problem to read this, because I am learning Russian language for 2 years now. Thanks for the pdf with the schematic .

 

[Gabriel07]

That doesn't tell us whether the amplifier section works. Try to get a cassette for testing.
Or does the radio have an aux input? Then try this input to check the audio amplifier section.

Ok, I'll try to find one.

 

[bertus]

Hello,

The transistors VT2 to VT10 make the amplifier circuit.
I also see some switches that lokely switch between radio and cassette.

Bertus

 

[Harald Kapp]

The common "first check" to make is to look for the supply voltages. Are these correct and stable?
This seems to be a rather old radio. A likely culprit for bad supply voltages are the electrolytic capacitors in the power supply (and elsewhere on the pcb). You can identify these in the schematic by the "+" symbol next to one pin and a high capacitance value, e.g. C36 in the top right of the schematic @bertus posted. On the pcb these capacitors are often comparatively large cylinders with a marked cathode "-" on the case ( I know, why mark schematic and real world component the opposite way? I don't know, that's how it is ).
For a visual inspection check them for leakage or bulging tops. Even if not visibly damaged they may have dried over time and thus have lost capacity. Often swapping the electrolytic capacitors for new ones (voltage same or higher, capacitance ideally equal, if not available use the next higher capacitance rating you can get) is all you need to restore operation of the radio (it is only a few weeks I performed that operation on a radio of mine which now again works like a charm).

 

[Gabriel07]

The common "first check" to make is to look for the supply voltages. Are these correct and stable?
This seems to be a rather old radio. A likely culprit for bad supply voltages are the electrolytic capacitors in the power supply (and elsewhere on the pcb). You can identify these in the schematic by the "+" symbol next to one pin and a high capacitance value, e.g. C36 in the top right of the schematic @bertus posted. On the pcb these capacitors are often comparatively large cylinders with a marked cathode "-" on the case ( I know, why mark schematic and real world component the opposite way? I don't know, that's how it is ).
For a visual inspection check them for leakage or bulging tops. Even if not visibly damaged they may have dried over time and thus have lost capacity. Often swapping the electrolytic capacitors for new ones (voltage same or higher, capacitance ideally equal, if not available use the next higher capacitance rating you can get) is all you need to restore operation of the radio (it is only a few weeks I performed that operation on a radio of mine which now again works like a charm).

So as I understood what you wrote here, means that I have to check every voltage on capacitors like C35, C36 and more, with the "+" symbol and make sure that everyone's voltage is stable and look for leaks and bulging tops. I have to check these with multimeter, yes?

 

[Harald Kapp]

No, not on every cap, only on power supply capacitors.

Looking at the other capacitors will be the next steps.

 

[bertus]

Hello,

Robotroom has a page on how to see if a bad is possibly bad:
https://www.robotroom.com/Faulty-Capacitors-1.html

Bertus

 

[Gabriel07]

No, not on every cap, only on power supply capacitors.

Looking at the other capacitors will be the next steps.

So ok, because I don't understand much about electronics, that means that I have to capacitors voltages on power supply, so power supply is a thing where I put the power cable in, yes? And if yes, so capacitor which is on power supply circuit I see C36, C35, C33, and C34, if I am wrong, don't judge me, the only thing I have done is put new cables on my moped, to make ignition...

 

[Gabriel07]

Hi, one more time. So I opened the back cover, unscrewed screws on the little board, and when opened it, it has a red C16 capacitor with a broken corner. Can it be something's problem? and I can't upload images, it's said that there is an error.

 

[Gabriel07]

Finally, I can upload photos, I just have to compress photo size.

 

[Harald Kapp]

I can't upload images, it's said that there is an error.

file size needs toe < 300 kB

C16 capacitor with a broken corner. Can it be something's problem?

Yes it can, but likely not the main issue.

so power supply is a thing where I put the power cable in, yes?

What I mean is the internal power supply: C24, C36, etc.
An easy check would be to power the radio with batteries. These produce a much cleaner power supply than mains power.

 

[Gabriel07]

Hi, i found a forum, and found audio amplifier section capacitors which I checked:
C35
C14
C15
C22
C23
C36

Checked voltage on every one, but my multimeter didn't showed that, and I don't know why. But when touching C35 capacitor, I hear silent cracks coming from speaker at maximum volume. when checking others, I hear nothing, multimeter won't even beep. What would that mean?