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
Hi Guys,
As I'm new to this forum but have a few B&O products eg, turntables 2402's 2403, etc, and B&O beomaster 3000/4000, 1600, beolab 1700. and then 4400.
The 3000(4000) no stereo, and balancing L & R not working only L yet output on both channels. This is what I do not understand.
The 4400 switches on briefly but then OL on for few mS thats it. I haven't really started allthough checked the drivers that seem OK.
Can I disable the OL switch and what happens?
What's a 2403? Photos?Check your speakers and speaker cables.
Martin
Hi Martin,
Apologise, Beogram 1202, 1203, and 1200. Does anybody know where can I Find preamp for the 1200.
Definately electronic, I'll start changing the electrolytics on the 4400.
Sounds like a channel down on your 4400...........
On the pre-amp?
You have described the perfect symptom of excessive DC voltage in the Output amplifier section - NOT the preamp.
Excessive DC voltage is dangerous - it stresses amplifier transistors and burns speaker voice coils, THEREFORE within a few milli-seconds of DC voltage being detected, the amplifier's protection circuit is triggered, opening the relay which powers the output amplifiers.
That's why the amp appears to work for only a few milli-seconds.
A major rebuild is required - replacement of some resistors, ALL trimmer potentiometers. ALL electrolytic and tantalum capacitors, and the majority (if not ALL) the transistors and diodes in the output section. And after all that, a recalibration of the amplifier.
Menahem
JFV,When you slowly power the Beomaster up from a variac, do you have any DC on the speaker outputs?If you do, check the output stage darlington transistors. Replace all in the affected channel if one or more has shorted.Then check the driver transitors and the nearest semiconductors. Replace the idle current trimmer and adjust it per the servicemanual.If the darlingtons are all fine, check the driver transistors. They are known to cause DC problems for no apparent reason.When you have found and corrected the present problem, you can consider restoring the whole Beomaster as Menahem suggests above.A servicekit with capacitors, trimmers, lamps etc. exists. But it's quite an amount of work and it involves a bit more instrumentation etc. sonot something most people can do "on the kitchentable".
Morning Martin,
Thank you for the reply, I do have 7 faulty Amps (All vintage B&O 4000, 4400, 1700, 1600, 1001's on my workdesk and three turntables and just started. I have also aquired an oscilloscope, I,m in South Africa, and these amps are ending on my work table.
I have made up my mind that if I found 1 faulty electrolytic i replace all. On the 4400 it's quit extensive job. You were right all the drivers are either leaking or faulty when tested. I have bought new replacement spares.
On the 4000 I have both channels working but no stereo, I'm still investigating.There must be something wrong in the pre-amp stages?
On the 2400 I have it doesn't come on at all. Here I'm also changing the electrolytics.
On the 1700 1 ch blown, I've aquired the blown parts.
I have 2 x beomaster 1001's, I havent opened yet.
Can you e-mail the service manual for the 1600, I have schematics, but one channel gets smelling hot?
Best regards,
JFV.