transistor heat excess and upgrade components

[boogiefreak]

hi, i got an early 90's solid state amp and , still working but the transistor (type 2sd2061 Rohm) just after power supply (circled in red on the photo)

and since i like the simple way it was designed i'd like to upgrade some components to improve the sound, so i'm here to ask some help about which components i can and i cannot modify

but before i've got to fix the excess heating transistor

thanks

 

[Mooly]

The heating is probably normal since its a series regulator.

 

[boogiefreak]

hi Mooly thanks for your answer, you think so (i'm not an expert) but it's hot it's burning when touching it, and it leave black marks on the top and ont pcb,
i've dissassembled it and tested it with multimeter diode mode and it's ok
i've looked around it and nothing seems burned

 

[Mooly]

Almost certainly its OK and the discolouration of the PCB is a normal chemical reaction to the heat. The only thing to check on parts like this is that the heat hasn't caused the soldering of the leads to crack and become intermittent.

Look at the middle leg of this power transistor. The solder has a ring around it where it has cracked due to heat. Very common problem generally.

 

[dragonweed]

Not an unusual problem with Japanese amps from those days,I have seen lots of discoloured PCB-s due to excess heat (worse, the transistor legs melting out of the board). If it concerns you, replace the heatsink with a bigger-black anodized- one (if you can fit it in).

 

[Welcome]

What amp is it? Looks like a good one. Upgrading it most likely won't be possible.

 

[boogiefreak]

ok, thanks again Mooly i think you were right, i've seen on another site with an amp from the same mark and serie that that this specific transistor got an over heating problem with the years.

Now i'm wondering i upgrading some parts will useful ? or a waste of time and money
like i've read on the net upgrading Capacitors, bypass power capacitors with polypropylene caps,
change carbon resistors with metallic ones
anyway, the amp is 25years old and need some components change.
what's your advices
thanks

 

[boogiefreak]

Hi welcome , the amp is a JVC AX-311

 

[Mooly]

what's your advices

My advices 😉

If its something you really want to work on and gain experience with, then replacing the small electrolytics costs peanuts, and given the age of the amp and the exposure they have had to heat from the pcb and the hot running parts... well that can only be a good thing.

The two large reservoir caps may well be absolutely fine.

Check it ALL for dry joints.

Is that a speaker relay at the front of the PCB ?

Such devices can give trouble by the contacts oxidising and causing distortion (not always very audible) and intermittent problems. The issue occurs because the contacts don't pass enough current to self clean them. If it can opened then its easy to clean the contacts by drawing a piece of clean writing paper soaked in alcohol through them. If its sealed then its a case of leave alone or replace with new.

I would not do much else beyond all that tbh.

 

[boogiefreak]

ok, yes it's a relay , i'm gonna clean it with cleaner spray (along with the potentiometers)
but for the caps any recommandations , suppose the cheap one won't bring nothing
ok gonna look for a not too much expensive of caps assortment kit

if anyone has more suggestion , don't hesitate , it's exactly that Mooly, i want to gain experience
thanks

 

[wwenze]

When checking heat and pretty much everything - dc offset, even noise and distortion, try comparing it against another identical or similar component. Like in your case the regulator transistor, the other heat sink below it is presumably for the other voltage rail. If they're the same temperature I won't care too much, even a 5 to 10 degree difference if it is explainable. But if one is cool and the other is scorching hot and they perform a similar task with similar designed power dissipation, yes then worry.

But then again it isn't unusual if the amp designer decides to give the positive regulator the additional job of running the digital and control circuit. A DAC can add a few watts and consequently more °C to the regulator.

 

[Mooly]

You would be best looking at recognised distributers of parts to obtain the caps. The caps in your amp are all 'radials' which mean the leads are at the same end. You can also choose a higher voltage rating. So if you need a 47uf 16 volts cap and a 47uf 50 volt cap then buy two 47uf 63 volt ones. These days a temperature rating of 105C is pretty common, yours are almost certainly 85C rated... but look at how long they have lasted.

Two examples, the 105C part is nearly four times the price of the standard item (which would be fine for your useage). Don't worry over cap lifetimes when you see 1000 hours. That's at its absolute max ratings, its many many times longer than that at less stress.

ECA1JM470 - PANASONIC - CAPACITOR, 47UF, 63V | CPC UK

EEUEB1J470 - PANASONIC - CAPACITOR, 47UF, 63V, 8X15MM | CPC UK

 

[Welcome]

Never buy electrolytic capacitors in a kit. You're guaranteed to get old, useless stock. Only buy fresh parts from a very big sources. Old caps are no good and standard fare for smaller stores.