Amp Repair

[Reddave101]

Hi all I’m a newbie to this, have messed with electronics for years but usually quite simple things but I’m now at a new repair I’m stumbled with? So hoping someone could point me in the right direction. I’ve got an old AIWA separates system which I love(had since the 90s) and worked my ass off to save for it £1300, well the other morning I turned it on and noticed the display on the amp and the tuner was dimmer than usual but thought it’s old and then 5 mins later both displays went completely off, looked at all settings etc to no avail. So thought maybe internal fuse had gone. Took cover off amp and noticed a cap had blown, happy days got spare caps. Replaced the cap with exact same one and all lit up perfect again until 5 mins later it dimmed and went off again. Same cap had blown, disconnected everything and replaced the cap and just let the amp run alone and 5 mins later it went again. After extensive googling it is a common problem with these units after a few years. The original cap is 100uf 10 v but suggested I upped the cap to a bigger v so installed a 100uf 35v but then I get no screen at all even to start with which to me is odd, as soon as put in 100uf 10v it comes back on for 5 mins??? I’ve got the service manual which contradicts itself, on the parts list the cap is a 100uf 10v, but on the schematic drawing it shows a 470uf 10v? I would try a 470 but don’t want to cause a mushroom cloud in the kitchen( wife might panic) the cap in question is C114. Just to point out ITs just the two displays that aren’t working everything else works perfect sound etc.. any help would be greatly appreciated

 

[Reddave101]

Drawing

 

[Grossel]

Please provide a schematic with decent image resolution so it can be read.

 

[Reddave101]

Better resolution sorry

 

[Grossel]

Well, I suggest you control the quality of your uploaded image first. If you did, you'll quickly see this is inadequade.

 

[Reddave101]

Well I’ve uploaded a second one with an adequate visual, I didn’t realise the first one wasn’t visible which I apologised for as they are screenshots of the manual

 

[rjenkinsgb]

How close are the capacitor joints to the transistor and resistors it connects to?
I wonder if one of those is faulty and being affected by the heat when you re-solder a capacitor?

 

[Reddave101]

There is quite a bit of distance between them, so don’t think it’s the heat but good thought, the pic makes the parts look really close but there is distance thankyou for the reply

 

[Reddave101]

Is it possible there is a dry joint? Maybe re-solder the joints on other capacitors etc... or am I barking up the wrong tree? Sorry like I say newbie to in depth electronics

 

[Ylli]

He's got a thread going in another forum (EP).
Did you check R104 yet? Lift one lead - what do you measure for its resistance?
Post the voltage you measure at Collector, Base, and Emitter of Q112, the Base and Emitter of Q111, and the voltage across Zener diode D105.