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
Some of you might remembers that on new years day, I blew the left output stage of my beombaster 8000 after a recap job of PCB5. (a huge thank to Beobuddy for it's kind help following that accident…). Being an amateur, the rebuilding of that output stage was beyond my capabilities… I've ask for parts from Martin (Thanks Martin) and finally found a technician around here to do the (expensive) job.
Job done: what was interesting is that even after the repair, the technician tested it to see if any other faults were remaining: the same problem was about to occur: it appears that the wire shown on the image below has lost it's connection with it's trace. Thus the problem. (I've put the schematic below for those who understand the repercussion of such a failure (I don't)… Fuse 2 has blown and one of the 2 big resistors of that PCB5 opened). The funny part is that my old TIP's are all showing good values. So it wasn't blown after all! Anyway I now have brand new TIPS with brand new heat paste and I reccaped the board, that couldn't hurt…
What i've learned: removing and putting back the left output stage is a pain in the ass DON'T FORCE ANYTHING. I my case, I had to desolder the speakers connectors in order to remove some wires in the way to let it out…but I've probably discovered that necessity too late.
…So after the repair, I went back to my technician, who never worked on B&O. He kindly accepted that I assist him in putting back everything in it's place, since I now know how to open everything and where everything goes. Then he would boost everything with it's variac and put the bias to spec…
What was supposed to be the happy ending is not: The microprocessor does not get out of standby, or shows random values (it always has been fully functional in the past though). However, bypassing relay 2 and unplugging P47 results in an (intermittent) proper behaviour: every programs could be selected, display is ok and, more importantly: I have a sound output from BOTH channels (at which point I asked him to check the no load current again just in case…)!!!!
So we closed everything and I went back home. It begins to be really expensive but unfortunately, i'm obsessed with it…I've unplugged, for now, the red and black wires of both outputs boards. (I'm also obsessed with the TIPS)
Everything tends towards a power supply failure (I think so I might be wrong)… After studying the schematic of PCB6 carefully I discovered that pin 4 and 5 of P48 should deliver 5V on standby. Mine only delivers 0.31 and 0.11V respectively (microcomputer disconnected) Also, the area around R55 and R56 is blackened: R55 show a value of 1036 ohms, so I guest it's fine but R56 shows a value of 862 ohms… (Maybe it's ok in the context of the circuit…???). C35 begins to show cracks around it…
….So there's obviously a recap job to be done here. But I would be interested in knowing what might have cause this failure since everything was working properly a few months ago, and for the last 30 years. Could the event described above have caused this failure? What would be the first place to look at and/or to replace?
Also, this board (6) seems relatively easy to pull out. But how to detach the infrared component without destroying anything?
Thanks for your help, support or any thought that could make me progress in this obsession…
Hi,
Sorry to read about your persisting problems :-(
After these attemps of (dis)assembling your BM8000, I would first start to investigate all (solder) joints. This machine has several weak points where resoldering is needed.
Several boards are connected through connectors next to each other, like boards 1,2 and 3. So, bad solderjoints needs to be fixed before you start with anything else.
Measuring can be misleading as sometimes yoU can measure certain required voltages, while ground leads can be broken.
These kinds of broken or weak leads in ground or supply leads can cause this kind of misbehaviour. Thats beside the required recap job which probably is needed. Btw do your measure on P48-2/3 5 Volts?
Thank's again for your time and help!,
P48 2/3 shows 0V. It might sound stupid, but here's how I took the value (maybe i'm not doing it properly): Multimeter on DC. I unplug the connector on P48 that leads to the microprocessor. I put the red probe of the multimeter on an exposed pin, the black one on the screw under which some black wires leads to the ground, just below the connectors panel... Both output stage are fully connected, with the exception of the black and red wires of each ones... 1 shows 0,28V ; 2-3 0V ; 4 0,31V ; 5 0.12V ; 6 11V ; 7 51V ; 8, 9 and 10 shows practically nothing 0.01-0.02 V.
Thanks for your time and help!
Guillaume
The brown board underneath those resistors is normal...
The ominous C35 and all the other red caps will have to go to the bin. Do this first, and double-check connections while you're at it.
Power supply stability is essential in this Beomaster.
Can you measure 5V at the regulator under C35?
Jacques
Thanks Jacques!,
We might be on to something... I have 4.4V at the output of that regulator, but nothing on p48 2/3. BUT I have continuity between these points.. I managed to remove the board... (I was so nervous with the infrared receptor... it finally came out with a kind of wire attached to it which appears to be a kind of rubber that protect the main wire (see the photo below...) I think I've done no harm...
C35 might have shorted so everything goes to ground? It clearly shows aging sign though...
At first sight, all solder joints on that board appears to be ok... I'll have to check with a magnifying glass though....
....Have you ever noticed how that receiver looks SO much better without it's back metal grill....?
Strange: R55, R56, and R28 of that board should be 220 ohms according to the manual. R55 and R56, on my board, are 1000 ohms according to the color stripes....
hamacbleu: Strange: R55, R56, and R28 of that board should be 220 ohms according to the manual. R55 and R56, on my board, are 1000 ohms according to the color stripes....
Be careful now, the manuals does not always show changes made during production. If the PCB was not repaired before it may be original.
Collecting Vintage B&O is not a hobby, its a lifestyle.
That may be a mistake in it: the schematic clearly shows 1k for these. the list of components shows 220 ohms. so there might be mistakes in the list of components
Some progress!! At last!!!...Jacques, you were right...C35 seems to have been the culprit.... Now it gets out of standby and every functions are displayed when something on the keyboard is pressed... it even kept my radio stations in memory... the volume encoder wheel goes from 0 to 6... everything seems fine.
Then, some smoke came out in the area of the rectifier...
Beobuddy, you we're right about connectors....The yellow wire was desoldered (could't it stop!!!) It appears that the smoke was coming out of the resistor above....Resoldered the yellow wire... the resistance of the burnt resistor still shows somewhat a correct value though (I measured 190 ohms).... but i'll change it anyway...
Question of an amateur: after a few seconds out of standby, a relay click is heard and goes clicking non stop. I put it back to standby instantly. Is it because i've disconnected both output stage from the 55V supply and the amplifier tries to boot them? Is that OK for now?
That's quite possibly the reason, yes. The burnt resistor seems to be critical according to the service manual. Do have a look.
If I were you, I'd dust off the innards of the Beomaster. But what a job to do eh!
Nice work then !
Thanks to the generosity of Jacques (Chartz), there is now the technical manual for the BM8000 on site.
Peter
Thanks Jacques for that manual! I'm now taking a pause on that: I'll have to find a replacement for the resistor, make a little cleaning and check all connections before I reconnect the output stage....
Then I don't know what i'll do: build a home made current limiter with a light bult in series as suggested by André or see my technician so he can power it up using a variac. (That would be a better idea, since he'll understand better than me the circuit and make further testing) I know that the left output stage is fully functional: it has been tested and no faults remains. But since I just recapped the right one, I don't want to see smoke again....
Beobuddy, in January, you told me that the 2 relays must be bypassed when doing this procedure. Do you use a fuse in between the short (just in case) and if so what should I use? Or is there another way to see if faults remains in the right output stage?
Still struggling!
It's been a week since went out of pause, trying to make something out of that receiver… I would now need some advice: Am I looking in the good direction?
After the output stages has been reconnected, the machine went out of standby, as it should and both channels and every functions were fully working. … but I heard the radio for only a few seconds
The 2 relays clicks, then unclick.
It seems as if the fault switch is triggered… So I went checking the values at the left output stage: The no load current is fully adjustable and the position of the pot, at 18mv correspond to the position on the right channel. Good.
But the DC offset is off by 15V at the speaker output!!!, impossible to adjust with R200. So I thought that somethings wrong remained in that output and that this offset triggered the fault switch and turn the amp off, (at least this part seems to be working...)
I checked the value on the right output, everything's fine. And the DC offset was near 0V.
On the left output stage, all connections to ground were checked. Continuity between everything…. I also thought that , maybe, 15V was not present on P38-2, but it is… I diode checked EVERY transistors B to C, and B to E, red probe, black probe, then compared with the values on the right output. Made a chart. Everything is corresponding. The resistors also shows good value… Caps are brand new, the brand new pot, R200 is unfaulty I'm at lost…. Here's the strange values I got:
Then I thought that, since the relays are switched off practically instantly, maybe it's normal to find a 15V offset: the manual clearly specifies to wait 30 sec. before taking these values. I can't since the 55V power supply is cut off a few sec after it's turned on…(That does not explain why the right output stage would behave correctly, under the same condition…or there's something I don't understand)
So I went back to the power supply and find out that 1.1V was present, on standby at P48-5, instead of the prescribed 5V... I followed the value to P76-6 of the microprocessor…the connection is good with R55…
My question: Is it normal to find a 15V offset on the left channel as soon as it is powered on? If yes, maybe my output stage has no faults and I should concentrate my effort on the power supply and solve the 1V on P48-5. Maybe this is the reason why the relays unclick : that pins is directly linked to them...
Thank you very much for your time and help! that thing as became an obsession: i'm starting to have dreams about potential solutions… It has become a passion though, so it's fun!
No. A 15V DC offset is not normal.Something is not right in that amplifier.Check the solder joints of the BF 85x driver transistors, they often crack.Can you get a DC voltage reading on the emitter of TR202 ? (the one that has 9-10V on it's base).
Martin
Thanks Martin for the fast reply:
Emitter of TR202 shows 0.9V...
The solder joints of the two BF 85x has been redone when the recap was made: one thing worth mentioning TR211 was changed for a BF859, although, after testing it, it was unfaulty, (every ICs of the output stage where proven unfaulty..) the other is still the old BF857 and shows good value...
An NPN transistor with 15V on the base and 1V on the emitter is no longer a transistor.
Thanks Martin,
in that case, if I can't rely on the comparisons i've made with the right output stage (which were taken on board), it might be a good idea to change all transistors present on that output stage... If this one is bad, chances are that the others might be bad too...
Well, I think it's time to quit: Ive changed every single transistors on that output stage....Same problem remains...The only thing left would be the resistors. but the values, compared with the right output were the same. (Not exactly the same in some case, but really near it..)
Or maybe the capacitors, although they are brand new, maybe they sustained something bad during the 1st failure? but they are not shorted or open, that is sure...
Although i'm ready to let go....Does anybody have a working left output stage to sell me?
Thanks for your help... (I'll post that in the "wanted" section)
(A good thing I've found on that construction is the screws they used: they are unstrippable!!)
I wanted so much to post of photo of my complete system in working order!
Have you checked all the printed tracks?
Sometimes, copper tracks break at the edges of their solder joints and it doesn't show, even under the thread-counter.
Thanks Jacques,
Yes, I checked the continuity between every single points on the board, I also checked the connections to ground. I replaced yesterday one of the BF.. copper traces came with it so I had to build jumpers with wire... (It took me hours!!) Tested continuity afterward and checked if there was no short. Fine.
...At least I've read and learned a lot throughout this process.
Wonderful B&O day!
After 4 months of struggling, countless hours of studying and dismantling, I finally made it!
A copper trace under TR207 was broken. When continuity was checked, I had it because the probe was pressed against the solder blob, making the connection. Last evening I saw a small line just below the solder blob, unnoticable without a magnifying glass. Put another jumper. Here's on the schematic where the trace was broken:
A huge Thank to everybody that helped me so far, especially Dillen and Beobuddy for their personnal assistance and time and Jacques for his support, his technical manual and for his quote:...copper tracks do break at the edges of their solder joints and it doesn't always show, even under the thread-counter....The machine has played for an hour and a half now, everything was put to spec, the heat sinks are less hotter, it plays better, it has no more distortion in the high frequencies in the left channel, every functions works, datalink with the beogram, remote...I'm more than happy. I may have done a lot of useless things throughout this process but at least, I've learned a lot ...I really love my 2400, but there is really a difference in sound! But I just acquired a beogram 4002, so i'll built another system with it...Thanks!!
Now the beocord...Guillaume Québec, Canada
Congrats Guillaume, had the same with my BM 4400, a PIB those broken tracks.
Congratulations Guillaume with your achievement, or better your victory!!
How many hours did you spend you say?
Bravo Guillaume ! (In French, there is a space before the exclamation mark!)
I am so happy for you. It always comes to little things like that, doesn't it?
I am also happy that you could find some support here, that's the whole point of the forum I guess... Long live Beoworld!
The Beocord: I've repaired four of those, a 6000, a 8000 and two 9000, so I know them pretty well (modestly: Martin has probably done dozens!). Tell us more.
Thanks!
One more question to close this thread. That may sound stupid but...
My whole system is plugged on a powerbar. Usually, when I finish using it, and everything's on standby, I wait about two minutes, then I turn the switch off on the powerbar, removing all the lot from the main. Like as if i'm afraid the system could start by itself or explode when i'm not there etc...
This is kind of a OCD... is it a useless procedure? or worse, is it something I should avoid doing?
Thanks for your help...
Jacques: i'll take a pause for now and get back to my old beocord 8002...Now that I understands better some elements of electronics, I might be able do do something with it! your help will of course be appreciated!
My Beomaster has been plugged for two years. I pull the plugs only when a storm is coming!
Congratulations! I wish I had the patience and resolve you and others have shown in the past year.
Regarding unplugging the system: there are some who believe you should always leave your amplifier powered on.
Well done!
Regarding keeping stuff plugged in - there are exactly two schools on the matter.
Pro-plug: Devices that have a separate stand-by mode are designed so that they can stay on stand-by indefinitely, so there's no particular reason to avoid it. Also, many failures happen when a device is powered on again after a break - but that is usually not the cause of the failure, it might have just accelerated it.
Pro-unplug: despite the best efforts of the designers, they cannot predict everything. Components age, and especially on vintage kit like this the stand-by power consumption can be quite large. It may have a non-trivial impact on your electric bill, and the constant warmth inside will cook certain components faster.
Personally, I unplug devices that I don't use daily or at least a couple of times per week. The rest will stay connected to mains unless a storm is coming, or I won't be home for days (to unplug if a storm was coming...).
Then there are the devices I don't trust to stay on. But I believe only TV sets are a known fire hazard, anything else actually catching fire (that spreads) must be extremely rare.
--mika
Thanks for all your thoughts...
Interesting: I never saw it as power consumption saving...Guess I wasn't that wrong after all. I imagine a balance between both procedures should be a good thing...
Well done, nice job.
I've had my fair share of broken tracks - a BM2400 was the worst of all. Kept going into standby after a few minutes.
I have a UPS for my stereo equipment. So, I leave it plugged in all the time.
If there was no UPS, I would unplug it. But we have poor-quality power in Israel. Lot's of brownouts during summer and winter, and the occasional blackout.