"Estrada 101" 4 channel soviet amplifier, 1st channel problems.

[ELS122]

I'm having problems with my Estrada 101 amplifier, when I turn it on, sometimes the 1st channel protection light doesn't turn off, but after around 3 minutes it turns off. at first, I thought it was just a sticking relay, but then after around half an hour, I hear a pop and smell something burnt, the amplifier 2nd channel (which I was using at the time) was still working, none of the protection lights came on.

so I turned it off, and the first thing I did was pull the 1st channel block/preamp out and look for anything there, and I saw the R39 resistor burnt, and nothing else.

when looking at the schematic I would think that there is no way for the R39 resistor to be blown with the correctly sized fuse F2, the fuse would've just blown.

maybe if pin 5 on the preamp block, if that gets shorted to ground maybe then, but I examined the rest of the amplifier and saw no place that it could be shorting.

Maybe I should take it more apart and look closer at the first channel circuitry

the protection light problem followed the amplifier 1st channel, not the 1st channel preamp board, so the problem must be in the amplifier
also, all the fuses are original ones and the proper value.

I've attached the schematics of the amp

[ELS122]

So I examined the amp and the schematic, I see no possible place for anything to short in the amp, unless the bakelite spacers went conductive that isolate the heatsinks on the output transistors from ground.

now the problem has moved to the 2nd channel, the protection light doesn't turn off on that channel, 1st channel doesn't have that problem anymore.

it seems the protection circuit senses when the output jumps up... I have no clue why it wouldn't work all of a sudden, I see no bodge fixes in the amp, even the screw ... warranty/security thingy was still intact implying that nobody has been inside this amp. none of the pots look like they'd been turned.

And I have no idea where C1 - C10 in the amp circuit are, I see all of the power supply caps but not the output coupling ones...

[ELS122]

So after a ton of thinking and probing around, I've come to the conclusion that the protection light is a sticking relay, and I don't know why the resistor got hot (after measuring it, it's bang on it's value even)... but it's no longer getting hot, not in any of the channels.

[Chris56000]

Hi!

Is there any chance you could scan all the pages of the book you got that from please?

There's a lot of useful additional information in Soviet manuals, including coil and transformer winding details, full voltage tables and layout diagrams, etc!

This would assist me in rendering an English diagram for you!

Chris Williams

[serg-el]

https://forum.cxem.net/applications/core/interface/file/attachment.php?id=448053
http://rt20.mybb2.ru/viewtopic.php?f=5&t=50600
http://offtop.ru/dustyattic/v1_720390_19_.php

http://radionet.com.ru/forum/viewtopic.php?t=16494

http://rt22.ru/viewtopic.php?f=5&t=55489

Check and solder the connectors.  Replace capacitors K50-6 (aluminum barrels).  Check power supply and output transistors.  The voltage map is in the circuit.

[ELS122]

I found those on the internet, sadly I don't have the book, mine even seems to be some later revision of the amp, since it has a small mod-board in the preamp blocks, and it is directly coupled to the output, not capacitor coupled like in the shematic

[ELS122]

https://forum.cxem.net/applications/core/interface/file/attachment.php?id=448053
http://rt20.mybb2.ru/viewtopic.php?f=5&t=50600
http://offtop.ru/dustyattic/v1_720390_19_.php

http://radionet.com.ru/forum/viewtopic.php?t=16494

http://rt22.ru/viewtopic.php?f=5&t=55489

Check and solder the connectors.  Replace capacitors K50-6 (aluminum barrels).  Check power supply and output transistors.  The voltage map is in the circuit.

That first link, the schematic doesn't match to my amp, not even close.
the link that has the pictures of the amp seems to be the exact version of the amp that I have, with the mod board in the preamp block.

the capacitors are not faulty yet, I'll make sure to replace all of the old paper capacitors and electrolytics in the future.
the problem is a sticking relay since it does click slightly, and the voltage on the relay is enough to make it switch off/on. but the light stays on and output stays silent.
I don't really care for the 2nd channel not working, later (probably when I change the caps) I'll take apart the relay and clean it.
I checked all the voltages on the output transistors, and the preamp board and they're all fine.

[serg-el]

So does the relay turn on / off? Is the protection lamp still on?
R9 in the amplifier sets the output zero balance. R26 sets the quiescent current. It is imperative to adjust the balance, otherwise the protection will work.
Check / replace C3 and C5 in the protection circuit.
C3 power-on delay. C5 delay during protection operation.

And without replacing electrolytic capacitors, repairs are pointless. They are 100% defective.

[ELS122]

So does the relay turn on / off? Is the protection lamp still on?
R9 in the amplifier sets the output zero balance. R26 sets the quiescent current. It is imperative to adjust the balance, otherwise the protection will work.
Check / replace C3 and C5 in the protection circuit.
C3 power-on delay. C5 delay during protection operation.

And without replacing electrolytic capacitors, repairs are pointless. They are 100% defective.

the light stays on, output stays silent
the relay clicks when I turn the amp on after a few seconds just like all the rest of the channels.
the amp worked perfectly 2 days before, I measured the DC voltages and the wire that the protection board senses (the output wire) is at 0.6Volts DC just like all the other channels

I'm 99% sure it's just a relay. when I take it apart again and clean the relay I'll post my results! 

it might very well be the electrolytics in the protection board as you said, but since I feel the relay click only once, as it should, I doubt it's that


also I wanted to adjust the balance but the trimmers were never touched, and it was close enough, so I didn't adjust it.
if I ever plan to use it actually for anything more than just ""background"" music at my home, I'll probably go back and adjust it!

[ELS122]

so I took it appart, messured the voltage on the relay coil pins, and the problem fixed itself... it seems by wiggling the pins around on the relay it got unstuck, or maybe there was some metal whiskey shorting the pins... idk, but it's fixed now and works fine