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This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Hi guys,
I'm currently working on a BM4400 TYPE 2419 (US version) with a weird overload lamp problem.
Here we go; when I turn the amp ON, the Overload lamp comes on right away.
After a little bit of troubleshooting were I concluded an overload problem on both channels, I decided to see if the overload circuit was functioning properly. Following the circuit to find my DC voltages, as soon I probed at the base of IC3, "click" protection relay engaged and OLOAD lamp came off! When the relay engages it remain engaged even if I remove the probe.
Now, here's the funny part, I decided to get the multimeter out of the equation to avoid impedance or capacitance changes and just used a bare wire and did the same test. Tapping very quickly at the base of IC3 also triggers the relay and the turn the lamp OFF. So I think not much it missing to get rid of the overload!
So here are the measurements:
R38= 4.7K
R40= 50
R41= 670K
R42= 700K
R44= 15.1K
Changed C18 without success
So far everything leads me to the capricious IC3 which is an MPS 5431 but I can't find anything on this transistor. Someone knows an equivalent? If this is the problem?
Thank you!
Nevermind...
The relay decided do operate normally but there is a true fault only on the right channel.
Will find out...