'VERY' loud buzz [resolved]

[Paul Birkeland]

Can you post some build photos? 

You can also try rotating the small speedball board up front 180 degrees so that the halves are flipped around feeding opposite portions of the circuit. If the 0V follows the half of the PC board you're seeing it on now, then you know there's an issue on the PC board.  If the 0V stays put in the amp, then there's something wrong with the underlying build that needs to be addressed.

[El Tel]

Hi Paul

How do I upload photos ?

Terry

[Paul Birkeland]

Reply, attachments and other options, attach: choose file.

[El Tel]

Here you go Paul

[Paul Birkeland]

There are lots of cold solder joints in those photos.  If your soldering iron has temperature adjustment, turn it all the way up.  If your solder doesn't have lead in it, I would get some leaded solder. 

The first step would be reheating all of the joints in this kit aside from those where LEDs are mounted (they are somewhat sensitive to being reheated after they have been sitting around for a long time).

[El Tel]

Hi Paul

I thought I'd also check the resistors on the Speedball small board, the 237 ohm 1/8 watt resistor on the good side of the board is reading 237 ohms as expected but the other 237 ohm on the side of the board where there's no volts at OA is reading 0 ohms, do you think this could be why there's no reading at OA ?

Obviously I'm going to have to change it, but i can only find 240R 1/8 watt here in the UK, are these OK?

[Paul Birkeland]

I wouldn't change that resistor necessarily. 

Your meter has a setting where it will beep when touching the leads together.  Get it setup to do this, then start touching pairs of leads on each transistor on that side of the board, then you may run into a pair of leads that's shorted out. 

It's pretty rare for a resistor to short to 0 ohms,  so I'd be looking for an external issue causing this problem.

[El Tel]

Hi Paul

I've done the tests on the transistors on the bad side of the pcb and yes they both have continuity, and buzz on the multimeter.

Can you let me know if these are the ones that I need to order as I'm in the UK.

https://www.digikey.co.uk/en/products/detail/central-semiconductor-corp/PN2907A-PBFREE/4806938?_gl=1*1sf5dg5*_up*MQ..*_gs*MQ..&gclid=Cj0KCQiAgdC6BhCgARIsAPWNWH0i2a-r8WVvCzaFxJjLPlQQksmUUl4V6LA11_TE-SxLiJjdtscIm2oaAmRAEALw_wcB&gclsrc=aw.ds

https://www.digikey.co.uk/en/products/detail/good-ark-semiconductor/MJE350/24613252?_gl=1*b0yvy7*_up*MQ..*_gs*MQ..&gclid=Cj0KCQiAgdC6BhCgARIsAPWNWH0i2a-r8WVvCzaFxJjLPlQQksmUUl4V6LA11_TE-SxLiJjdtscIm2oaAmRAEALw_wcB&gclsrc=aw.ds

Many Thanks

Terry

[Paul Birkeland]

Those will work.

[El Tel]

Hi Paul

A quick update, it's all OK again, all reading measure as they should again.
Turned out that replacement of the two Transistors and the 237 ohm resistor seemed to do the trick.

Thank you everyone 👍

Ps - I learnt a little along the way too, so all in all what's not to like 😉