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 have just bought a 'spares or repair' Beomaster 2400-2. It is in fair condition, and I would love to get it working again, and wondered if anyone could offer advice as to how to do so.
It is not showing any signs of life when plugged in. Internal fuses are fine, and mains power is getting to the transformer. Output from the transformer seem ok (?) at 15 and 22V. The relay does not fire either - and when manually bridged, the unit still doesn't power up.
Does this sound like a straight forward / common problem, or something more difficult to sort? I can tackle any basic checks / component changes, but detailed diagnosis would need an experienced hand. I have read that some / all of the caps would benefit from a change.
Please advise,
Dan
Welcome to Beoworld
Is the red standby dot lit ?
Martin
Thanks Martin
No, no lights at all...
Check DC voltage across C92 (large axial capacitor at the end of the main board nearest to the transformer).
Check the DC voltage at the emitter pin of TR31 (with respect to ground). That's (edit: NOT!) the transistor sittingon the inner side of the socket bay metal housing, not far from C92.(edit: The transistor on the metal is TR27).
Martin - thank you for the pointers.
C92 is showing 21.5VDC across it. I managed to track down TR31 - but it was not where I expected it on the metal housing next to TR27, but further back, towards the heatsink. It isn't showing any voltage at the emitter.
Check voltage on all three pins of TR27 (with respect to ground).
Martin,
TR27 is showing 20.8 on the base, 0.18 the collector, 21.4 on the emitter.
I see.Without mains connected, put an ohmmeter from the collector pin of TR27 (that's Testpoint TP16) to groundand let me know the reading.
I'm getting 13.1 ohms there Martin,
Take out capacitor C97 (note its polarity) and measure the same place again.
Right - thanks Martin. I'm not sure how best to remove the main board - it seems quite tightly wired to the other boards when I attempt to remove it from the bottom. Can it be accessed from the topside?
Normally you never have to take out the whole board.You can just lift one corner at a time but in this case you can just desolder one pin of C97 andmake sure the pin sits free in its hole without contacting the solder pad.
Live troubleshooting - I had to get out the schematic to follow this!
--mika
Same result with the C97 out,
Have you checked the bridge rectifier?
Jacques
Then put an ohmmeter across the collector and emitter pins of TR31 (still without mains!).And you can solder back C97.
chartz: Have you checked the bridge rectifier?
With some 20V at the emitter of TR27, we can rule out the rectifier.And 13 Ohms to ground at the collector of TR27 is wrong.
The 13 Ohms on the emitter of TR31 would look more correct if they had been on the collector (because of the lamps etc.).My theory at this point would be that TR27 has died because TR31 has shorted C-E.If Dan confirms a very low resistance reading across TR31 C-E, I'd say he will have to replace TR27 and TR31.I would probably also replace TR30 and Zener D51 to be on the safe side.
28.5 ohms here,
Thanks.Hmm. That's a little higher than I expected.Can you take resistance readings from ground to all three pins of TR31 respectively;Ground to CollectorGround to EmitterGround to Base
And where do you connect your meter to ground in the Beomaster ?
Strange things going on? Or maybe I am doing something wrong:
Ground to Collector - 15.1Ground to Emitter - 13.8Ground to Base - I'm getting out of range here - so extremely high resistance
I am taking the ground from the -ve feed from the rectifier - i.e the large track that runs across the centre of the board and connects to C92s -ve side. Is this not correct?
It's a fine ground point.
The collector resistance looks pretty much as expected but the emitter is wrong and we have tolook a bit more into this;Apparently, the 28 Ohms across TR31 C-E comes through ground.Take out TR27, TR30 and TR31 (note their orientation etc.) and measure the resistance from thethree solder pads where TR31 sat to ground again.
I've taken those three out, and the resistance is the same on the three pads of TR31...
OK.We have now ruled out a lot of possible culprits but we will have to isolate this even further;Take out the tonecontrol and the right side light panels. Two screws in each panel, one or two plugs in the right panel andtwo soldered leads on the tonecontrol panel and put them both aside.Measure the TR31 emitter pin resistance to ground again.
Hmmm, that was tricky. I am still getting the same resistance on the emitter, though.
We are now down to either C97 (which you already checked - check it again, this time remove it if possible!) or ashort somewhere on what remains connected to the emitter solderpad of TR31.A lead goes out from the emitter to another place on the large main board.Following the connection on the board, the leads and down on the board again, look for bent components touchingeachothers leads, metallic debris or similar that could introduce a short.
I have removed C97 and get the same result. I have also checked, as much as possible, the rest of the board, the tracks and the components, and can't see anything obvious - everything is looking ok.
The only thing is, it looks like it may have gotten damp at some point, as there is quite a lot of blue/green oxidised copper in between some of the tracks, and some crusty looking parts, though this is not widespread. Could this be causing issues?
Is it time for the great B&O graveyard in the sky, or is there anything else to check?
Email sent to you.
Hello all!!
I have a Biomaster receiver 2400 receiver paired with 75 series speakers and a RX2 turntable. I love this system and have 2 more 2400 for parts.
All was working fantastically until today.
The 2400 Reciever has worked fantastically up until today.
No music/ sound produced on phono, tape or radio. All lights (volume, base, treble balance, phono, all stations, and standby power) on at this point except the green power light in the on/ off switch under the lift up panel not on.
I switched the on/of button under the panel thinking this was the problem. Now- no lights at all except the green standby power light to the far right of the unit.
Martin has asked in several other "no power" conversations/ forums if this light was on. Those were not however mine is.
All of your help is much appreciated.
John
Opps- It is the red standby power light that is on- not the green light,