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
Hello all,I'm the happy owner of a white Beomaster 2000 type 2801, which unfortunately has begun acting up recently. the F101 fuse keeps blowing and I subsequently only get sound out of the right side speaker outlets.
I'm not particularly knowledgeable about these things, but could the fact that I've been powering a pair of Beovox S45's (4ohm) and a pair of CX100's (6ohm), be the issue here? Unfortuntely the fuse blows even with just the S45's attached.
A few days before this issue started happening, I also replaced all the bulbs with new ones, purchased from a member here on Beoworld. They work great, as did the amplifier for another weekend, before the fuse started blowing.Any help would be greatly appreciated!Mathias
Unrelated to your speakers, if you can measure about 4-6 ohms resistance across the speaker terminals, when disconnected from the BeoMaster.
Your electrolytic capacitors in the regulated power supply section, and your output amplifier section are completely dried out.
The little red/green/blue teardrop tantalum capacitors are likely all completely useless.
Time for a complete overhaul.
I've restored countless numbers of these BM2000/3400 series.
It is a magnificent machine, well worth restoring.
Menahem
Good evening Menahem,First off, apologies for the late reply. The plight of my Beomaster got lost in life there for a second. Both speakers measured 3.6 ohms of resistance, is that cause to worry or close enough to your expectations.In any case you're probably right, a total recap is likely in order. I'll see where I can order new ones and get started.Thank you for the reply! Mathias
Recap'ing, that could be a good idea - but I suggest you look for the cause of the present problem and fix that first.A blowing fuse F101 points to a problem in the left channel output stage, most likely one or both output stage darlington transistorshave shorted.IC101 would be my first guess, but even if only one has shorted, the other one (in the given case IC102) will have suffered an overload andboth should ideally be replaced in any case.
Martin
I have now replaced the two darlington transistors, IC 101 and IC 102. The fuses don't blow now, but the left channel is still not working, no music just a loud humming. I have tested the cables going from board 6 and there is music comming in to board 7, also on the left channel, so the problem must still be in the amp circuit for the left channel.
Does anybody have a suggestion for what the problem could be?
Could any of the caps cause this?
My guess is one or more of the other 8 transistors, but I am clearly just guessing.
Did you set the idle current?Do you have any DC on the output?
No, I did not set that. Is that the same as "No-Signal-Current" adjustment explained at the end of the manual?
I will do that tomorrow, and measure DC on the output.
Thank you
Yes, that's it.
I have tried to set the Idle current by following the directions in the manual, but I am not able to measure anything on the resistor or the darlington. I tried to measure the right channel as well but I can't get any readings. My meter is not the most professional, but it has mV and mA.
Here is the meter I have http://www.amazon.com/Uni-T-UT58D-Digital-Multimeter-Sinometer/dp/B00VZ6UJ1I
I do have -30 V DC on the left output, nothing on the right, so there is still something wrong with the left channel.
I'm still going to emphasize, just to eliminate any unknowns, to replace all the tantalum and electrolytic capacitors in the output amplifier.
Without an oscilloscope, which could help us solve the problem in a few minutes, sometimes covering all bases in a cap replacement is necessary.
Yes, there's definitely something wrong in the channel that produces 30V DC.- And no capacitors in this circuit can cause this fault.The problem will most likely be somewhere from TR103 onwards.Check the fuses, the output stage transistors (and their insulation towards the cooling fins), their emitter resistors, the driver - and predrivertransistors and the low-resistance resistors (10, 270, 680 Ohms etc.) in the last stages of the amplifier.You cannot set the idle current in this channel.The working channel, however, should be possible.I'm sure that multimeter is fine. Make sure to put it in DC-volts mode and for idle current measurement you shouldbe using the 200m range. (That's about 3 o'clock on your meter).