audio-talk

brig001 wrote:If you keep the negative probe of the meter on the negative supply rail, check the voltages on all four speaker terminals. I would expect about 22.5V DC on each.

Brian.

OK done that they all register around 22.5 each

brig001 wrote: If all this checks out, I would check to see that each channel operates independently. So if you connect both speakers and only give a signal to the left, does it only come out of the left speaker. You can also check the right channel the same way.
Brian.

Checked that. when i plug either speaker into the left side they work independantly. right side does not work. when i disconnect the left interconnect. no sound. when i disconnect the right interconnect, no change.( left side only works). swapped the interconnect around and the left side only works.

Set your meter to the 200v DC range (or something similar), hold the black probe on the outside of the phono input plug (either one). Then touch the red probe onto each loudspeaker terminal. See what voltage is on each of the terminals. Do this with nothing plugged into the amp (speakers or interconnects).

I noticed when I was using it that if any on the output terminals was shorted to ground that side would go into protection and shutdown. That may have happened to the right side.

Nick wrote:Set your meter to the 200v DC range (or something similar), hold the black probe on the outside of the phono input plug (either one). Then touch the red probe onto each loudspeaker terminal. See what voltage is on each of the terminals. Do this with nothing plugged into the amp (speakers or interconnects).

I noticed when I was using it that if any on the output terminals was shorted to ground that side would go into protection and shutdown. That may have happened to the right side.

Ok i have tested all 4 loudspeaker terminals and the outside of both phono plugs. the results are 22.8 left and 22.7 right. what does that conclude?

is it time to try waving the voodoo bones over it
how would i test to see if the input capacitors are working properly?

Ok, that shows that all the terminals are floating as they should be. So if you connect a speaker to the right side only, and apply input does anything come out?

Nick wrote:Ok, that shows that all the terminals are floating as they should be. So if you connect a speaker to the right side only, and apply input does anything come out?

Right side only no sound
left side only is good

It sounds like the output stage is OK, which is good news. I would look at tracks around the capacitors you changed. Are they the white ones, bottom right on the photo? The track for the top one is visible, so I assume it is the bottom one which isn't working - always the way.

If it were mine, I would either:
Remove the capacitor for the faulty channel and inspect the tracks.
Or, find the track which goes from the capacitor to the chip and carefully scrape a little lacquer off so I can get a contact with a meter probe and see if is connected to the capacitor lead.
Or, Since the track appears to be on top, I would be tempted just to solder the capacitor lead on top of the board as well as underneath. It is possible that the plated through hole has been damaged during the surgery.

It is hard to tell which option I would use without looking at it.

Good luck,
Brian.

Took the lower capacitor off. the Amp worked as before(left channel only)
soldered the cap back on with a big bit of solder. there are three solder poits on each side of the cap, I think for different sizes. I tried joining 2 of these solder poits together to get a better contact. It did not work. still only left channel works. How would i test to see if the capacitor has current going through it or test the points where the cap solders onto the board?

If it's a 2050 I would think there's 2 resistors after the cap to bias the chip to half the supply Voltage? Could check there if a signal is getting through but need something to 'see' it with.

Had a look at the board again today and followed Brian's advice. I found the tracks leading from the capacitor and scraped some lacquer off to expose the metal. I then soldered this to comnnect it to the cap.
Hey presto it is working

Well done

There you go

The ubiquitous bad joint

Well after the Owston disappointment when i could only get one channel to work, i thought the old problem had returned. Got the amp home and took the lid off. One of the capacitors had come loose in transit and the capacitor leg was under some tension so it had sprung loose. rectified this error. maybe you can hear it at the next Owston meet where i hope to have tweaked the speakers a little to bring out more mid and low range.
One day I hope to build something and it work first time

Isn't hindsight wonderful, if we'd known and if we'd brought a soldering iron ...