ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Problem #1: One of my Penta amps is not doing well. As it warms up, a crackle/static develops, grows louder, them "pops". The static will stop, then gradually start up again. If I continue to play the amp for a while it will go into orange mode. What should I look for to repair?
Problem #2: I really feel stupid for this one. I was upgrading a spare Penta 1 amp, new opamp, re-capping. As I was testing my completed project, the input bracket shorted against the bottom of the circuit board, small sparks, and sniff of smoke. I think I'm going to be sick. Now the amp goes orange when I try to turn it on. What might have I damaged?
Thanks in advance for a reply to either of my woes...
//Bo.A long list...
Thank you very much BO for your reply!
1. I suspected as much...that one is easy.
2. This could be a challenge. Being that the amp starts red, then goes orange upon an input signal, any hints as to which semiconductors I should replace first? Are you including the output transistors in your statement?
cordobaman: Are you including the output transistors in your statement?
Are you including the output transistors in your statement?
Yes, that's likely.
/ Johan
Orange light may indicate shorted/broken output transistors. Measure them and replace if found faulty. Measure all semis in the areas where you had the short. When powering up use a light-bulb dimmer with, and slowly increase voltage. Monitor zero-voltage current.
A broken/burned ground trace on the circuitboard could also be the cullprit.
BTW, small detail, it's Monitoring the output zero-voltage and idle current.(30mA/30MV accros R103/104 or a bit less).