Hi !
I've purchased a pm450 for cheap. It was very dirty so I decided to clean it, especially pots cause they had noise
I asked the previous owner he doesn't know anything he bought it as is. I ordered pairs of the power transistors. And as I really needed the amp for another project I tried to redo what I cleaned previously. When I connected the resistive wire with the emitter and powered on whole vu-meter was on maximum without signal so rapidly powered off and tried to connect base but it seemed I don't cleaned well the welding between emitter and the tin so as it powered on there was a spark at the base of the transistor and powered it of. As I rode in the datasheet this transistor outputs 6v at the emitter and it's getting 45v at the collector, so I assume a short circuit between could have done more damage than just frying the transistor.
I'm really new to electronics so clearly it was not a good idea to try to wire things randomly. I'm studying the service manual with diagrams to identify testing points at various stages of signal to see what is damaged. It's a good opportunity to learn about patience and electronics.
My question is do you think the excess of tin was a makeshift repair for a faulty transistor ? or it was from factory ? as I rode that power transistors have to be soldered with generous amounts. I've mad all the possible mistakes by rushing and made more difficult to understand the starting situation. But if someone has a clue it will be helpful.
I've purchased a pm450 for cheap. It was very dirty so I decided to clean it, especially pots cause they had noise
An externally hosted image should be here but it was not working when we last tested it.
. During disassembly I came across this. An externally hosted image should be here but it was not working when we last tested it.
I tested the transistor with my multimeter, and seemed okay. So I cleaned what I just thought to be excess of tin, assembled everything and powered on. There was no output, nothing on the vu meter. I asked the previous owner he doesn't know anything he bought it as is. I ordered pairs of the power transistors. And as I really needed the amp for another project I tried to redo what I cleaned previously. When I connected the resistive wire with the emitter and powered on whole vu-meter was on maximum without signal so rapidly powered off and tried to connect base but it seemed I don't cleaned well the welding between emitter and the tin so as it powered on there was a spark at the base of the transistor and powered it of. As I rode in the datasheet this transistor outputs 6v at the emitter and it's getting 45v at the collector, so I assume a short circuit between could have done more damage than just frying the transistor.
I'm really new to electronics so clearly it was not a good idea to try to wire things randomly. I'm studying the service manual with diagrams to identify testing points at various stages of signal to see what is damaged. It's a good opportunity to learn about patience and electronics.
My question is do you think the excess of tin was a makeshift repair for a faulty transistor ? or it was from factory ? as I rode that power transistors have to be soldered with generous amounts. I've mad all the possible mistakes by rushing and made more difficult to understand the starting situation. But if someone has a clue it will be helpful.
Something like a dim-bulb tester, or simply adding a few hundred ohms of series resistance between the supply rails and the amps will allow for testing of the amp without blowing things up due to high current faults. Limit the current, limit the damage is the rule with solid-state amps. This is while working on the amp without load (when it doesn't need much current).
Thank you for precious advice, it seems very wise to do so.
Imgur: The magic of the Internet Here the picture again. I'm very curious to what it was.
Imgur: The magic of the Internet Here the picture again. I'm very curious to what it was.