JVC 4mm-1000

[bingobelle]

Hi

some background of me first. I know more or less nothing about recievers and are no electronic guy. However I´m a electrician since 20+ years and know how to solder, know the very basic about analog electronics. I know what a capacitor, diode, transsistor is and so on. also know how to measure them with my multimeter. It is a decent multimeter. ( fluke 87 serie iii )

I also know that electrolyte caps have a tendency to leak over the years and since my reciver is nearly 50 years old and never restored I guess the capacitors is in some case not so good.

So I opened the thing and for what I can see a lot of the bigger caps have leaked. there is some brown stuff all around more or less everyone of them. At least the bigger ones. I have written down all the caps acording to the voltage and fahrad capacity and going to order them.

so I will try to get this thing in working order again. the sound is working in one channel but in the other it is very very bad. most humming and scraping sound. not music anyway. tried to switch speakers, front and rear output and so on but that does not help. but there is sound in both left and right so i guess the "end amp" is in working order.

i think i will change all the big caps that looks to be leaking and clean the potentiometers with some contact cleaner.

I will also upload a picture of it.

so, what do i want? well, since I know very little all input is greatly apreciated. i have taken away 2 caps already ( very vissible on the picture, 1000 microfahrad and 25 volt just to make a test on them. i think it is the circuit board that transform ac to dc but not sure. my fluke can only handle up to 5 microfahrad but according to the manual i coulld use the ohm measurement and on 40 Kohm it is supposed to take 33 seconds for the multimeter to charge the cap. ot took about 45 seconds. i know that this is not a very precised way to do it but i guess that a supposed 33 second charge that takes 45 seconds indicate that the cap is bad and also a lot of brown stuff on the circuit board there the cap where sitting. and i guess many of the caps will have different ratings now 50 years later compared to when it was new.

i did clean the the circuit board there the 2 25 v 1000 micro fahrad capacitor sat so it was much more brown stuff before. looks worse in real than on picture.

so, any kind of guidelines and general input is greatly apreciated.

please bare my bad technical english, I´m from sweden and found technical english to be a bit hard sometimes.

Thanks

Christian

 

[goodolpg]

Sometimes that "brown stuff" is glue and the cap may be fine. Glue can cause issues of its own. Some brands are known to have used glue and the issues it can cause are a known problem.
Are the top of the caps expended/ballooned, or has the shrink wrap label slid off the top of the cap and down the side?

 

[bingobelle]

Hi
the shrink wrap has not slid of the top and the tops are not expended/balloned.

all the caps are elna caps.

 

[bingobelle]

Anyone who can explain the different functions on those recievers. thinking about matrix 1, matrix 2, norma tape chanel2.4 and mono. I know what mono means but do not understand this matrix 1 and 2 stuff or tape chanel2.4

if using FM radio mono gives most volume. then matrix 2 and matrix 1. on normal there is very litle sound.

using AUX input with for example my laptop setting normal gives most volyme but nothing on matrix 1 and 2.

the instructions says the reciever is ready for the age of 4-chanel FM broadcastinf but then you have to plug in a 4-chanel decoder into aux-2 and switch on the switch 4-chanel on on the backside.

with no reason at all there is now good sound in both speaker on the rear out. but still bad sound on one of the front out.

have tried the pre-amp cables from both front and rear to the front main amp and still bad sound so guess it is something in the main amp.

 

[bingobelle]

I think I have come to the conclusion that two of the integrated ic amp is bad. they are stk-20d. anyone who knows if I can check them somehow with a dmm if i take it of the board. like you test a diod or a transistor?But between what legs? there is 10 legs numbered from 0 to 9. is it possible at all to measure them to see if they are shot? I mean, I cant be 100 percent sure that it is not something else but I think it is those ic amp that is shot.

I re-soldered those two and first the sound was way worse, then after a second re-soldered the sound is back but still no volume.