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! I have a Beomaster 1000 (type 2317) with a problem. I use it only as an amplifier and, although most of the time it works very well, occasionally one channel or the other will cut out and fall silent.
The symptoms are:
Couple more notes:
Since nobody popped up to say "oh that sounds like X", I decided to go ahead with some of the general suggestions for ageing BM 1000s in other threads. This one has all the original components as far as I'm aware, by the way.
To start with I checked the 30V line (it's good) and the bias settings. For the latter the service manual says to measure voltage across a resistor at the corner of the two channels' stage 3 sections and adjust the 5k trimmers to set as close as possible to 24mV. Because the 30V setting was spot on and I don't think anyone has ever messed around in here before, it was a surprise to find both channels were quite far out: 6mV on the right channel and just over 3mV on the left. So I adjusted these - they were a bit noisy when turning though. I'll run it for a while and see what difference it makes.
The next step I assume would be to replace the old capacitors, starting with the biggest ones. I will probably do that regardless, since I'm in the mood.
Chris
Give the speaker switches a little shot of contact cleaner and wrk them a couple of times.Tighten the speaker socket contacts by inserting a very small screwdriver or similar tool behind the contact leafs and prod them a bit to increase contact tension.
Martin
Thanks! I thought the speaker sockets were making decent contact, but I will take a closer look.
By the speaker switches do you mean the ones activated by the speaker I and II piano keys? Is there an easy way to get better access to these switches? They seem to be on the underside of a small board that is rather hemmed in.
cannam: Thanks! I thought the speaker sockets were making decent contact, but I will take a closer look. By the speaker switches do you mean the ones activated by the speaker I and II piano keys? Is there an easy way to get better access to these switches? They seem to be on the underside of a small board that is rather hemmed in. Chris
Maybe this can help
Collecting Vintage B&O is not a hobby, its a lifestyle.
With the top cover off you can spray them from above as they are.They are open enough to let contact cleaner seep through to the contacts inside.
Thank you Søren - that's a really useful thread, I think I probably did read it, some while ago, but I had forgotten a lot of what was in it - and Martin. I'll report back at some point I hope.
In the meantime, and I'm sure this will be no surprise to anyone here but me, the bias adjustment has made a remarkable difference. It hasn't cut out at all since then, and I had lost track of how much I was doing to subconsciously compensate for it - even choosing music that would be less likely to provoke the problem. Sounding great now in fact.
There is some quiet popping when no music is playing - regularly at about one-second intervals in one channel. I think this was probably happening before as well, but didn't seem important then.
If I may recommend something, then get a cap, lamp and trimmer kit from Martin, we know from experience that the most of the caps are off specs by now, the lamps will fail, if not tomorrow then at a later date and the new trimmers will make it easier to make the needed adjustment. Why repair if not broken, some people may say, I see it as needed service, like when you get your car serviced, if one or more caps starts to fail totally it may cause harm to other components and make a bigger repair needed. The popping sound you can hear is a sign that something is wrong and it may be worse with use.
Thanks for the tip - though I have a pretty good supply of capacitors already, and can probably re-cap the whole amplifier section with appropriate replacements if it should come to that. I'm a bit reluctant to put in the work all at once, because I'm lazy because this is my main amp and I would rather listen to it than take it out of action and risk messing something up into the bargain.
I don't have trimmers or bulbs to hand, although I can see that replacing noisy trimmers could be a very good idea. Do the 5k bias trimmers have the same pin arrangement as a typical contemporary 3-pin top-adjust sort?
The initial cutting-out problem hasn't come back since I adjusted the bias - I've cleaned the switches and so on, but I suspect the bias really was the cause.
The popping sound is a regular series of soft pops on the right channel, just after switching on (when it starts loud and quickly diminishes to quiet or silent) and occasionally in silences in music or between tracks (quietly). Anything that repeats like that makes me think "capacitor" but obviously even if that's right, I have no idea which.
I have now replaced the lugged power supply filter cap and the pair of big output caps - makes no obvious difference to the sound of the amp or to the popping noise.
cannam:Do the 5k bias trimmers have the same pin arrangement as a typical contemporary 3-pin top-adjust sort?
Yes, I normally use Piher PT10LV10, and buy at Mouser
Turned out the faint popping sound I mentioned actually came from the source. Doh! So all is well.
I did replace a handful more caps - the 400u/40V power supply filter and the four easily-accessible 100/35V ones down in the corner - to no obvious effect, but that's probably a good thing. I will replace the bias trimmers, because the right one in particular is really very noisy.
I'll probably stop there for the moment - I have to weigh up the benefits of sprucing things up against the risk that I damage something in the process, or that the new bits aren't as reliable as the old (which in this machine appear to be impressively good for the age).
The FM tuner still doesn't work - it just emits occasional crackly spikes as you spin the dial. I do have a proper FM aerial plugged in. The signal here is poor, but other devices can still pick up a few channels. The test points mentioned in the manual all seem to call for an oscilloscope, which I don't have. I haven't touched any of the trimmers on the tuner or IF stage - apart from turning all of those at random, is there anything I can try here?