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Hi:
Would like to seek advice from the forum on a Beomaster 1900 that I'm restoring.
The unit powers up but goes into standby by itself after 3-5 minutes. When powered up all source selection works properly. The radio and audio amplifier plays fine.
What's been done:
1) Unit has been fully recapped.
2) All light bulbs work.
3) Output transistors all working and re-soldered to eliminate cold solder/cracked joints. Amplifier plays fine. Sounds good, no clipping or DC.
4) TR22 - Standby transistor replaced.
5) 2IC9 - Electronic replaced.
6) 2D50- 15V power supply bridge rectifier replaced and upgraded to a 6AMP unit. Old one was running uncomfortably hot.
7) Transistors in fault switch working.
I notice that when you press the a source key and standby simultaneously the relay starts chattering and the lights flicker. Also the volume level selection automatically increases. Is this normal?
When the unit is first on, everything works properly and sounds great until it decides to go into standby. You can turn it on again but will not stay on for as long. Usually revert back to standby after 30s or so. If you let the unit stay off for 5 minutes or so you can power it back up and it play again for a few minutes.
Anybody else run into this and have some experience?
Thanks,
Derek
Assuming all lamps are correct (wrong wattage lamps can cause the strangest problems).
Have you checked the two SAS570 ICs?It's rare to see them fail, but it does happen.If you don't have an IC to test with, you could try swapping the two and see if the symptoms change.
Also check the oscillator on the volume board for the touchpads.
Martin
Hello Martin:The unit appears to be original and has not been opened before.
The lamps are original.
I swapped the SAS570 ICs. The unit behaves the same.
"Also check the oscillator on the volume board for the touchpads."
The aluminum front panel is removed and so I'm touching contact pins wth the fingers.The volume control works fine. Increments and decrements properly to the touch. Unless you meant something else?
The oscillator on the volume board is used by all the sensorpad circuits.Does this Beomaster 1900 have the remote control option installed?
Hi Martin:No remote option. The remote control portion looks unpopulated.
Hi Derek,
Interesting problem. I haven't seen that specific issue before. From your description I would look at 2TR30, 2TR31 and 2TR32 as well as the surrounding components. Maybe just re-flow those solder joints first and inspect the traces. The problem appears to be heat related so a component maybe failing at some temperature or a trace/solder joint is opening up at some temperature.
Those components are grouped together near the back part of the circuit board near 2IC301. You might be able to get to them with some cooling spray to see if cooling them down allows you to turn them back on sooner. Temperature issues can be difficult to nail down.
John
Hi John, Martin:
Just wanted to close the loop on this one. I was thinking heat related problem too, because from a cold start, the radio runs for several minutes before shutting off. And once warm turning it back on will cause it it to go off very shortly.
Turns out that the problem is 2TR29 in the power supply. It was a hard one to find, and I only got to it by replacing the transistors (not the ideal way to trouble shoot) in the power supply. The challenge is that the transistors test fine on the multi-meter but are either leaking or intermittent with heat.
Anyhow... it works now!
Thanks so much for chiming in to help.
Very good Derek.I have had a few cases like that too where a transistor measured good on a tester by itself only to fail in circuit. Those are fun.Good work,