transistor amp not working after shorting output

[sg97]

pair that is attached to amplifier board thats in amp is working other two from missing board was burned

 

[anatech]

Okay, so we are really wasting time here unless you can tell us make and model. Please make it easy on us.

 

[sg97]

i can tell you model but its not available online it was old amp a local production so its not really popular. i can provide pictures. btw i only needed a opinion i dont have to replace transformer it works ok as is so i dont want to bother you.

 

[Netlist]

Show us your goodie

Hugo

 

[sg97]

its a big old comunist amp from 70s or 80s i am not sure xdd btw i want to restore it in function at least i dont have all electronics from it as i mentioned before other half of the amp is long gone someone removed it for parts i think. also i only managed to make volume pot to work rest of them are not working also board thats for the potentiometers is in unknown condition because voltage that i can tap on to on psu board is low like 9v, so thats why i said someone replaced it with japanese one xd 16v and to amp board gets like 24v i guess psu board is raising voltage somehow. its sad how people who do not know electronics ruin such a device, its really sad, also heatsink from other board thats missing had one randomtransistor that was burned so someone put a random transistor some time xd. i will fix eq board and i will do a paintjob so it will look nice i forgot to mention i got it for 20$ with shipping xd it is a good project for me to restore i like doing it.

 

[turk 182]

i guess most of us are wondering what makes you think "half the amp is long gone"?

or is it just that the reverb tank was stripped out?

 

[sg97]

its what i see, it was really in bad condition most of the wires are removed and also things like pots and audio jacks also other two transistors that are burned are not part of the board thats present in the amp now
thats what i see.

 

[Netlist]

If the remains of that amp are in such a poor condition, I propose to keep it as a decorative object.

Hugo

 

[romeoleung]

Possibly the schematic is similar.
https://www.elitesecurity.org/t505384-Cajavec-ra-popravak

 

[sg97]

amp works but it needs stronger transformer but it works like this anyways. it needs a paintjob thats for outside. inside i only have to fix tone board and to add that transformer thats all rest is small deal.

 

[sg97]

romeoleung it is similar, model that i have is not that common at all xd​

 

[sg97]

toneboard works on 24v but issue is tha all potentiometers failed and no longer works i tested them. its due to age xddd

 

[sg97]

or i can order one of those premade tone boards from the e bay and call it a day xd

 

[sg97]

tone board is really in bad shape, i measured all resistors they are ok for caps i cant really measure them but visualy they look ok. there are a lot of small components transistors or regulators i am not sure but i dont have any idea whats wrong, when i put all pots back there is some clues that it works i was able to adjust eq a bit but it seems like its not grounded. really strange i am not sure how to fix this if anyone is having a idea i am here to listen. here is a picture of the tone board. btw pads for potentiometers are damaged i can fix it later but thats not a problem. if you guys can give me a suggestion what can be wrong here i will appreciate it i am scratching my head for days because of this xd

 

[anatech]

Hi sg97,
Tone control pots do not go to ground. Have a look at some tone control circuits.

 

[sg97]

I did not do anything with it I only removed old pots that did not work. Also when I removed that purple wire it did not work at all. Strange I am not sure what's wrong here. When I said it's not grounded I mean when I power it and attach it to the amp it makes buzz sound like it it's not grounded I did it with few amps so I can be sure it's not the amp issue. I have no clue here

 

[sg97]

also i forgot to mention if i brige these two resistors i get a sound from input but a ton of buzz its almost unlistenable.
i really want to fix this board i can get those 3 band eq boards from aliexpes and add a eq and volume but i will loose all the other functions of this amp. so i have to fix that toneboard but i dont know how xdddd 😂😂😂😂

 

[anatech]

Hi sg97,
Without a schematic, or a huge amount of experience, you will not get anywhere. You must either replace or repair the circuit (replace the pots with similar values). Replacing the circuit with something else may be the start of a pile of trouble.

 

[sg97]

i can replace potentiometers but i am not sure if that will fix the issue i am having.

 

[anatech]

Well, you said they are bad. Okay. Tone controls are normally part of a feedback network. If the pots aren't there, it will not work properly. You could tack in fixed resistors to mimic the centre position of the pots and test from there. Don't expect it to work without the controls (or sub) present.