Hey all,
I finally fixed this amp and since it was kind of an odd fix I figured I'd explain what was wrong in case others run into this issue.
I DID replace the main amp IC on a whim; although, I should have trusted my gut instict that it was not in fact the problem. The reason I didn't think it was a problem is that when I turned the amp on, there was absolutly no sound from the speaker. No pop, or thud or speaker movement at all. Anyway, replaced the main amp IC and still no output, so I pulled out my trusty O-Scope and an electric guitar and started scoping the signal path. I had output after the main amp IC and was baffled at that point.
For those of you who do not know this amp, there are 3 choices of output: speaker, headphones, or external speaker. The headphones jack and the external speaker jack are for 1/4" plugs and the connectors for each of them are configured to be normally closed if there isn't a cord plugged into them thus sending the signal to the internal speaker. Well, as it turns out the jack for the external speaker was bent such that it did not make it's normally closed contact and the output signal stopped right there.
I did not have a replacement jack of that type, so I pulled it off the board and completely removed the contacts from the back of the connector (this was the signal not the ground) and then soldered it back onto the board. I then soldered in a permanent jumper across the thru holes that were now missing the pins that I removed. It rendered the jack useless; however, why would you want to hook a seperate speaker cabinet up to an amp like this? It seemed silly to me, plus the owner agreed.
Problem solved... :tu:
I finally fixed this amp and since it was kind of an odd fix I figured I'd explain what was wrong in case others run into this issue.
I DID replace the main amp IC on a whim; although, I should have trusted my gut instict that it was not in fact the problem. The reason I didn't think it was a problem is that when I turned the amp on, there was absolutly no sound from the speaker. No pop, or thud or speaker movement at all. Anyway, replaced the main amp IC and still no output, so I pulled out my trusty O-Scope and an electric guitar and started scoping the signal path. I had output after the main amp IC and was baffled at that point.
For those of you who do not know this amp, there are 3 choices of output: speaker, headphones, or external speaker. The headphones jack and the external speaker jack are for 1/4" plugs and the connectors for each of them are configured to be normally closed if there isn't a cord plugged into them thus sending the signal to the internal speaker. Well, as it turns out the jack for the external speaker was bent such that it did not make it's normally closed contact and the output signal stopped right there.
I did not have a replacement jack of that type, so I pulled it off the board and completely removed the contacts from the back of the connector (this was the signal not the ground) and then soldered it back onto the board. I then soldered in a permanent jumper across the thru holes that were now missing the pins that I removed. It rendered the jack useless; however, why would you want to hook a seperate speaker cabinet up to an amp like this? It seemed silly to me, plus the owner agreed.
Problem solved... :tu: