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Hi,
new here. i have had a Beomaster 2402 for several years, got it from a boot sale in UK. sometimes its been a bit crackly but no major problems. I now live in Australia (same mains power as UK) and it has recently fused. Both 1A fuses in the back blow when its turned on. I had a look inside (I have some amatuer electronics experience) and it looked like the 5000uF power capacitor had burst. I got three replacements for the big caps, all 4000uF 75V (closest I could get) and replaced them. When turned on, get same result, just fuses. I can't see any other fused components and it is fairly clean inside. Anyone have any ida what could be causing this? Can a faulty transformer do this? I opened up the transformer and its sealed unit - nothing unusual visible inside...
Thanks for any help, any pointers to whoever else might help would be great. Really don't want to bin this!
Theo
Welcome to Beoworld !
Separate the transformer secondary to rule out the transformer.Transformer good? Then move on to the rectifiers (there's one on the main board and a larger oneon the chassis.Put an ohmmeter across their secondaries to see if they are loaded too heavily.Check for shorted output stage transistors and/or bad idle current trimmers.
Martin
Hi, thanks for the reply. Sorry, I don't know what any of that means. I will post some pics. I don't know what the transformer secondary is. I can see the rectifier attached to the transformer but not any others. Where are the output stage transistors?
Thanks,
Capacitors after replacing.
View inside.
Sorry for my slowness.. I now realise that by 'Separate the transformer secondary to rule out the transformer.' you mean just disconnect the output of the transformer? I will try that now.Thanks.
Ok, progress. :) so I disconnected the transformer output shown. Plugged it in and the power lamp now glows steady and nothing fuses. What next??
...just need a bit of help with this.. "Put an ohmmeter across their secondaries to see if they are loaded too heavily.Check for shorted output stage transistors and/or bad idle current trimmers."
Thanks.
Oh, that's a Beomaster 3000 (possibly type 2402).I thought you had a Beomaster 2400-2, - not that it matters much, really becausethe principles are the same.
And don't get me wrong when I say this, but if what I wrote above makes littleor no sense to you, you may not be the right person to tackle this fault.And I mean this in the best of ways, for your safety as well as that of the Beomaster.
Anyway, based on your findings so far it sounds like a burned outputstage to me, - a problem that in these DC-coupled amplifiers can put eventrained tech guys to the test.
no offence taken! But I do have some electronics experience, its was just the terminology confused me. I was hoping it was the recitifier. I have taken it out, a ITT B80 C5000/3000. I'm just wondering if I can test it and replace.
OK.. I do know how to test a diode, and my meter readings accross the rectifier do not look right:
from 'red' input to output is low (resistance)
from 'white' input to output is high (should be low)
from earth 'out' to red and white input is high resistance (should be low)
Hope this makes sense, but it looks like all but one (red to + out) diode is blown.
Is its worth replacing this, or is this just indicative of a more complex fault?
You are right, that if its more complex, I am probably stuck and it would not be worth me getting this fixed professionally, in which caseis there somone who would want it for parts (pay shipping only)? I don't really want to just bin it, its too beautiful.. although I have thought of perhaps just putting a modern amp inside it (sacrilage!!).
How high is "high" and how low is "low" ?
If the diodes in the rectifier are open circuits it won't blow the fuse(s) but one or more shorted diodes may.The diodes may go open circuit from overloading, that can happen if a circuit after the rectifier has shorted - and thatwill typically be an output stage (or both).
'low' is zero and 'high' no reading, on my meter. I guess this means it could be the output stage. But is it worth replacing the rectifier?
Thanks
Well, the rectifier is dead then.But why ?The rectifier itself may be the only bad component but you won't know until you've checked a bit more;With the Beomaster unpowered put your ohmmeter across the red and white/red leads on the rearof the amplifier board and let us know the reading.Then put it across the four emitter resistors, one by one, and let us know the readings here.They are most often red (or grey) ceramic components and they sit towards the rear of theamplifier board, close to the driver transistors (with the star-shaped cooling fins), not far from whereyou just measured. You may have to scrape a little red or grey paint away from their pins to bare enough metalto measure on.
Edit: Being a moderator, I have taken the liberty to edit the thread title to ease searches etc.
Between red/white and red leads, its zero, because they both connect to the same contact of the centre power output cap. If I disconnect those pins (they unclip from the board) the reading is 128K. The reading across all four red resistors is 1ohm.
Very good.
Now, with the red and red/white leads lifted away from the board, we need the readings across:- The pin where the red lead was at the center of the rear edge and the black lead in the rear corner of the same board- The pin where the red/white lead was and the black/white in the opposite rear corner.That's the power supply lines to the two amplifiers.
Hmm. the reading is not stable and climbs steadily from about 20K, settling at 50K. Same for both sides. (no power connected of course, perhaps my meter battery is a bit low.)
That could be correct.Then go directly onto the output stage transistors at the rear chassis.Measure across emitter and collector on all four.
left to right looking from the back, they were: 10K, 35K, 35K and 35K. Again not very stable to read, but tge leftmost was definitely lower than the others.
Thanks, hope this is getting somewhere!
Does your meter have a diode tester function ?If it has, please use this for testing across C-E on the output stages.Expect readings of apprx 0.5-0.7V.(swap meter leads/polarity if you cannot get any results within this range).
ok, no, unfortunately don't have that function.
A bit difficult to move much further.The 10K is a bit weird when the others are so close but there doesn'tseem to be any shorted output transistors so I suppose it would be OK toreplace the rectifier (if you haven't already done so), fit new fuses and test it.Test without speakers first.
Ideally, a variac with mains current monitoring would be the place to connecta unit like this but unfortunately that's not part of a standard household.It would have given us an opportunity to power up slowly and "carefully" rather thangoing full power at once, plus it would provide a certain electrical safety.
Hi, can you tell if the capacitors are wired correctly? Negatives are all to the right in the pic. Thanks.
There are several different versions but if you compare to this (seems to be same version), it looks right.
http://archivedarchivedforum2.beoworld.org/cfs-filesystemfile.ashx/__key/CommunityServer.Components.PostAttachments/00.00.35.78.67/BEO3000_5F00_optres_2D00_2.JPG
Success! With new caps and rectifier, (generic 200V one) its working perfectly. Sounds much better too, the crackle and pop on turning on has gone. Very happy. Looking forward to another 43 years of groovin' (the amp, not me!).
Thanks for your help Martin,
Well, a bit of luck never gets in the way, does it ?