Hello everyone!
A friend of mine retired and gave me his oschilloscope, a Leader LBO-520A.
After 15 minutes of operation, the oscilloscope stopped working.
I opened it and i found R437 burned. I replaced it, but it burned again after some seconds.
I checked the ESR of all capacitors on the power board, they all seem fine.
I checked all outputs of the transformer, all seem fine.
I replaced Q436, nothing changed.
I tested Q423, it seems working fine.
I have about 500V across R437 when i measure dc voltage.
Anyone can help so i can repair thios scope?
It means so much for me and my friend, he got so sad when he saw it dying..
Thanks for your time,
Regards, George