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
greetings all,
it is that time again when I am looking for the “Beomaster specialists” help/advice/pointers.....
it started with a complete recap job......finished now, except the big reservoir caps - all trsted well within spec.
the 1st roadblock after that was a wild switching of both relays on the start-up board....that was rectified
by replacing both crystals on the uP board and while that happened I decided to replace both uP sockets
with high quality tulip style ones.
after adjusting the no-load current the next roadblock: adjustment of the DC offset didn’t work....!
this was rectified by replacing 5TR201/202 with a closely matched pair as well as the R200 trimmer pot.
the next issue was a failing frequency wheel.....one pin of the 8-way ribbon connecter had a broken wire.
temp fix applied until the replacement cable/connector has arrived.....frequency can now be changed .
Coming to the main question:
I can tune in stations, pre-set stations but the output volume keeps unchanged, no matter what I dial on the volume wheel ??
the sound apears clear but only at a very low volume on both channels ???
what did I miss here ?
help urgently needed.....đđŦ
ALF
Hi Alf,
The blue wires from the sensor assembly on those wheels often come loose in their solder connection to the button board. Check those.
Also verify with the Beomaster 8000 remote control that you can operate the volume control. If neither the remote control and wheel don't work then it is some problem inside the BM on the Microcomputer board or maybe with the volume control IC circuit on the Filter & Tone Control board.John
Hi John,
great to read you were interested to deliver some “first aid” đđŦ
i dis-assembled the control panel and checked all soldering - no wires were loose.
when I turn the volume-wheel I can see the volume-indicating display part is changing but It doest not translate into any increase in volume ?
i can also operate the volume with the remote....same result.
i checked the tone/filter board #4 again for possible cracked soldering and connections.....all good ?!
next check was along those ribbon cables and their attachment to their plugs (i discovered one broken wire on the frequency wheel connector to the uP
board which is now repaired) and measured for resistance to make sure there are no cable breaks...all good.
so, I guessit is down to my favorite....the uP board !!.....unless....?
one thing I found odd is when I turn-off the BM it takes quite a while until the signal meter goes down and the last whisper has turned to silence....
almost like a slow capacitor discharge ??
well, now it seems to get very hairy ? I don’t expect the unit to turn on if the output transistors would be dead, wouldn’t it ?!
making a mistake in connecting the boards the wrong way also seems not look very likely, although........đĄ
i keep searching....this thing has to work again after all the effort that went into !
If the remote control doesn't operate the volume control then that pretty much eliminates the wiring between the control and the board. You will have to dig in and see if the control signals to the volume control device are operating. Is the volume IC getting commands?
John
One thing I don't have clear understanding of from your problem description is what exactly doesn't work regarding the volume? I was thinking you were saying the volume wheel does not change the volume level on the display. As such it does not change the actual volume you are listening to.
Second, you said you can hear audio but at low volume levels. Does that mean the volume display shows the lower volume setting?Is that low volume setting then stuck there (since I take it your volume control does not work)?On the remote control test my understanding that like the volume wheel it doesn't work. So attempting to increase or decrease the volume means the volume display remains fixed on whatever number you see (something low). Is that a correct run down of the problem?
thanks again for taking time to analyse the issue.
what happens is the audible volume seems to be stuck at the lowest level, no matter what I do ?!!
when turning the vol wheel the numbers on the display do change - same thing when I use the remote for that - but the audible volume does not change !
which would indicate as you mentioned that the designated vol control IC may not get commands ?
is my understanding correct ?
That is one possibility. I had one Beomaster 8000 where the volume control also changed on the display but with no sound at all. When I checked some test signals going into the preamp and to the output amplifier board I discovered there was no signal. So the problem there was somewhere in between. That is the Preamplifier board or the Filter & Tone Control board. The volume control (attenuator) IC is on the Filter & Tone Control board. In my case the problem turned out to be the connector that carries the audio signals from the Filter & Tone Control board to the Output Amplifier boards. That is connector P24. It is the one located towards the back, under the FM signal strength meter. The connections there were poor but reseating the connector and fixing it so it couldn't come loose fixed my problem.
To help isolate your problem you can insert a test sine wave (1KHz) into the Tape 2 source input, select TP2 on the Beomaster and monitor the signal coming out of the P24 connector for whichever (or both) channels you inserted the test signal on. In other words, disconnect P24 so nothing is going to the Output Amplifier boards and connect probe wires on the P24 pins of the Filter & Tone Control board (P24-1 = L, P24-6 = R, P24-4 = ground). If the audio test signal is not following the volume control at that point then drop back to TP203 on the Filter & Tone Control Board and check the result there. Also verify the voltage levels for the attenuator circuit per the schematic.
Hello John,
in the meantime I did check if there was any voltage change at 9IC3 & 4 when turning the vol wheel.....which was the case.
I shall revisit the tone/filter board and the vol control IC.
another thought that worried me is the actual signal I can hear , asking myself whether this is just “cross talk” ?
when I change from FM to any other inputs like TP1/2 or PH I can still here that very low vol FM signal.....? That can’t be right
or is this another problem pointer ??
The crosstalk you hear should not happen but several BM8000 owners have experienced it. I haven't had that problem on any of my Beomaster 8000 restorations yet. I know and believe it happens though. My guess right now is that problem is due to failing multiplex switching IC components (on the preamp board - IC102 & IC202) where the source is selected. That IC (AD 10/278) seems to be impossible to find. The fact that you can hear it though would seem to indicate a signal getting from the preamp to the filter & tone control board and on to the output boards. So I would still checkout the filter & tone control board. The crosstalk (or bleed through) is a separate problem. I can't promise you a replacement or a timeline but I am working on a replacement using a modern multiplex switcher designed for audio. I will let you know if and when I get that done.
I suppose there is also a possibility of a voltage/ground problem causing the source switching to not work properly. If you have a breadboard you could mock up a test circuit and test your AD 10/278 multiplex switch devices.
Ok John,
first back to the tone/filter board 4P24:
found a cracked joint at pin 6 which triggered an intensified recheck on that very board with no further findings.
checked the attenuator circuit voltages as suggested, all pretty good except the 0 V which was between 15 and 20mV
Next was a re-check of the preamp board, looking for cracked joints again around the connectors....no findings.
what I noticed however were signs of previous “repair work” on one of the AD10/287 ICs looking at the “amateurish” soldering ?!?
I wonder if it is possible at all that those switching ICs can get in a “state of limbo” so no input is properly switched...a kind of in between state ?
the reason for that question: connected an iPod to TP2......no audio signal audible at all !
looks a bit like playing the waiting game until your project of a “modern audio switch” had lift-off ? Or finding a couple on ebay...........đŦ
as a precautional activity I resoldered all connectors to be on the safe side, sadly no rewards regarding THE issue at hand.
It sounds like some previous owner tried to fix or modify the input switching.The AD 10/278 multiplex switcher can be a prime suspect. I would de-solder and clean up the previous work to see if that helps. On the dead TP2 input problem there are a couple of other suspects. One is the input volume trimmers on the preamp board (the ones that have the adjustment knob that sticks out the left side of the cabinet). Those get dirty and I have seen a couple fail. Another suspect is broken wire connections for the input source DIN jack in the input source panel. You can test those issues by sending a test signal into the TP2 DIN jack and checking to see if it is present in the preamp prior to the AD 10/278 switch.
great minds think alike đđ, although this seems slitghly “unbalanced” !
i did indeed unsolder and put back in place (hope dies last)...no effect.
the big trimmers were already earmarked for replacement and are on their way.
sadly I don’t have. mouser or similar shop around the corner to get these excotic trimmers exceot from overseas,....pretty sad I think !
I will follow up on the DIN plug lead and will also be on the look out for a AD7110 chip - it almost looks like this could be the trouble maker
in regards to the volume issue ?? Fingers crossed......another good reseason for you to finish that multiplex switcher replacement project for the AD10/278
chip đđ¤đ
PS: why isn’t my post visible on the forum,.....or am I blind ?
Hi Alf,I always figured that if I had to replace the preamp source input trimmers that I would just use normal board mounts and adjust them from inside. Once adjusted they probably aren't changed much. Original types would be desired though. Where did you find some?The only AD7110KN replacements I have found (other than from another Beomaster) are on Ebay (from China). Sometimes those work out though so I am ordering a couple to tryout.
the trimmers are from Telec Electronics Netherlands and the seller is on ebay under ‘posttrade’
Piher has so many different types so it took me a while to get to the correct type.
yes, you are right with the AD7110 chip.....has to be china......I may have to go down the same path unless my local contact,
a retired B&O repairer with a vast amount of spares, does have a couple AD10/278 and AD7110 chips in his vault ??
Won’t hold my breath.....if he has some left I will buy them all and perhaps enough for us ?!
will be in touch
its probably nothing new to you but on the matter AD 10-278 chip:
Terribly sorry but my local source had unfortunately only one of each, the AD10/278 and the AD7110KN đŦâšī¸
But, Is it worth trying the 4053 triple 2-input analog multiplexer CMOS chip as a replacement ?
Sorry, should read ‘....4053 triple input 2-channel analog multiplexer....’
ALF: Hi John, its probably nothing new to you but on the matter AD 10-278 chip: Terribly sorry but my local source had unfortunately only one of each, the AD10/278 and the AD7110KN đŦâšī¸ But, Is it worth trying the 4053 triple 2-input analog multiplexer CMOS chip as a replacement ? ALF
It does looks like the TI CD4053 multiplexer can do the job. However, it is not a direct plug-in replacement. You would need an adapter board plus you need two of them. I think this Maxim MAX4758 IC would be better. One IC handles both left and right channels. Of course it also requires an adapter board but there would be just one board connecting to both the IC102 and IC202 pins (the AD 10/278 ICs removed of course) on the preamp board.
It might be worth trying the CD4053 though so go for it :-)
yes, adapter board....I am squeezing my brain out about that ! The original is a DIP14 chip, this TI chip a DIP16 âšī¸
Kept looking at the circuit diagram again and again......one thing: both the switching issue and the volume issue are connected
to the slave processor.......can we rule out a faulty slave processor đŗđđŦ ??
PS: the two AD7110 are ordered.
ALF: Kept looking at the circuit diagram again and again......one thing: both the switching issue and the volume issue are connected to the slave processor.......can we rule out a faulty slave processor đŗđđŦ ?? ALF
I never say never but I think it is unlikely. One way to tell is to measure the signal from the microcomputer board that instructs the volume control what volume. That goes for the quality of the control signal for the selected source. Only one source should be selected so if those control signals look good then I would say the microcomputer board is okay.
There still could be a grounding problem too.
On an adapter board I think it is better to have one adapter board that handles both channels. The preamp has the two AD 10/278 ICs very close together so creating a common, single channel replacement might be more difficult than one that plugs into both IC spots. You also will want a good layout. The phono audio source inputs are very small amplitude signals compared to the FM and TP2. I wouldn't want to jumper them around the board with plain wires. You could end up with new noise problems. I would prefer to go with a modern surface mount switching IC and an adapter board that is small with wire runs as short as possible.John
i looked at the slave processor again and checked the voltages for the vol and input source commands
and it looks like you are right.
at the associated dB values both (left and right channel) show about 4.9V, about 35mV in between.
the same can be said about the input source switching voltage - so it looks very much like that processor does its job!!
thanks to chinese new year celebrations there will be some wait - as usual - for the attenuator chips AD7110KN
see what happens once they have arrived ?!!
in the meantime I decided to abort that AD10/278 chip replacement......just too far outside my skills đĸ
I’ll be back
some good and bad news to continue......
good:
i checked the AD10/278 multiplexer switch pair on PC3 according to block diagram of AF, SM 2-2 and it looks like the switch is working,
showing 4.9V respectively and about 30mV at ‘others’....not quite the 0V though !!
Bad:
finally received those attenuator ICs AD7110KN from Hongkong....put them on sockets but no change to the failing volume issue ?!!
checked those voltages associated with the Buffer Amp.....TR201/203/202/204 etc ....all good.
looks like I hit a decent road block ?!! Even a uP selftest was fine.....TP ! đ
next thought was the memory chip got stuck on mute but I can store any volume and it stays as set , so rule that one out ?!
But, where else could I check ? Any further ideas / pointers ??
BTW: did you find those big trimmets for PC 3 .
I would expect the analog switch to be working as far as selecting sources since you were able to do that earlier. The problem with the failure is that there is crosstalk from an unselected source (FM). The volume control problem is a mystery though. Refresh me on the problem...both channel volume levels cannot be adjusted via the volume dial or the remote control? The volume indicator does work though and you are storing various levels? So you can dial up a volume level like 3.0 on the display but there is no volume on the output?Just to double check your amplifier output can you disconnect the audio signal (the two pin connector) to each output amplifier? Then connect your oscilloscope to measure the signal of the disconnected audio cable. Input a test sine wave to TP1 or TP2 and watch the signal on the scope as you increase/decrease the volume.
Regarding the big trimmers on the preamp board I haven't found replacements yet.
thanks for coming back to me.
good news first:
here are the two ebay item #s for those trimmer pots fir the preamp - just type in the numbers on ebay and aa 50pOhm and 25kOhm trimmer comes up
# 320529279718 and. # 320685607813 - that should work !
back to the volume issue on my BM8000:
yes, I can adjust the vol level with the wheel or remote and the respective numbers come up on the assigned display but I can not hear!! any changes !
two simplified explanations:
1 either the tone/filter board has another problem not yet discovered and / or those attenuator chips don’t work so the output boards don’t get anything
or
2 both output stages are more or less dead.
anyhow, these ar my thoughts.
sadly I do not have a sine wave generator but wouldn’t any other source do just fine ?
It seems odd that both left and right channels would have the exact same problem if it is the attenuator IC since each channel has its own attenuator. It's possible but kind of suspicious. Anyway, in the absence of a normal lab signal generator there are various mp3 files of sine waves you can download and feed to the Beomaster TP1 or TP2 inputs. The main thing is to check the audio signal coming out of the Filter & Tone Control board so verify the test signal is there and it's amplitude changes with the volume control.
I can't remember, on the attenuator circuits, did you modify anything regarding R146/R246 trimmers and the related fixed resistors (R143, R145, R243, R245)? Also the Opamp IC6?
The common things between the channels are IC6, the supply voltages, ground and the microcomputer supplying the volume level selection. You verified those volume level control logic signals right?
Brilliant idea with the mp3 sine wave files...should have remembered, as I had a signal generator downloaded on my other PC !
burnt a 1kHZ sine wave test disc...that is the good news - thanks for that genius suggestion.
no trouble of seing that sine wave on the scope but not so good when verifying that wave via TP1 input and it certainly does not increase its amplitude đĸ
looking at the signal on 4P24 pin 1&6 .... no sign of a clear sine wave đ¤Ŧ
yes, I also thought about 4IC6 and will check this out - I have not made any changes regarding R146/246 and their fixed resistors.
I previously checked the signals at 9P80 at different volume readings/levels, verifying that table in the SM 2-2 which looked ok.
luckily I have a donor unit coming from Germany which hopefully provide opportunities to test/change over parts.....provided they are ok !
.....will be back !
I forgot about another common opamp...4IC5
Also, you do see your incoming sine wave to the attenuators at 4P27-4 (Right CH) and 4P27-1 (Left CH) ?
Regarding the volume control microcomputer board signals you verified at 9P80 (Right CH) and 9P83 (Left Ch)...I would check them on the other end (the Filter & Tone Control board) - 4P28 pins 3 through 8 (Left CH) and 4P29 pins 1 through 6 (Right CH).
Intermediate confession......I did replace both trimmers 4R146/246 with the specified value, but did not change anything.
now checking that sine wave test signal as suggested.....and replaced 4IC5 and 6.
will be back....
While you are doing that verify the attenuator control lines either on those Filter & Tone Control board IC devices or on the connectors.
Check ground connections on the tonecontrol board.There are two.
Martin
Yes Martin, thanks - guess I found them - they are ok.
Had to pause proceedings âšī¸
Those ribbon cables are becoming a serious roadblock as I identified a couple of broken wires.
I will check the donor unit if they are any better - If not I probably have to get on to Steve an have some new ones done.
right now it makes no sense to continue until this problem is out of the way.....also noticed both speaker switches are suspect.
next stop seems beolover for some replacement.....
well, you never walk alone đ¤Ŧ
will report back
Just to be clear...which ribbon cables are you talking about here that you found broken wires?John
A couple have been band-aided so far like 9P83, 9P78, 9P79 and 9P81 but that is definitely not the correct way !
those 9Pxx connectors are very fragile and should be replaced - that is why I want to see whether the coming donor unit has better ones
or Steve at sounds heavenly will be contacted. I do not have any neccessary tools to fit the ribbons to their plugs đĸ
Ok,
after a lenghty wait I am back on track, or should I rather say back on double- track ?!!
the donor unit has arrived and much to my surprise looks far too nice to salvage......perfect display
and the rest has been completely re-capped, excl the 4 big capacitors.
now I feel like sitting between chairs....which one to prioritise
the BM -which started this post- is still waiting for the speaker switch replacements from Beolover - both of the original switches
are mal-functioning đĄ, something I discovered by accident.
the donor unit shows the standby dot when plugged in, I can turn it on...except both relays on the startup board won’t energise/switching ?!
meaning nothing audible đĸ
while waiting for those speaker switches I checked the PS board 6 from the donor, reflown all connector headers, tested all involved transistors off-board
........nothing faulty to be found. All three voltage regulators deliver....?!
I can measure about 23.4VDC at D2, associated with RL2, but nothing at D1/RL1......which bears the question: is it likely both relays are faulty ?
I somehow doubt that, but.......?!? So, in other words it is very dark right now...not particularly up-lifting.
any further words of wisdom ?
It is a good problem to have where your new Beomaster is in great cosmetic shape. That means another future restored Beomaster 8000 can go back into service.
I never trust a non-restored Beomaster 8000. They are too old now. I wouldn't risk doing any further electrical damage to it until the capacitors have been replaced, the connections checked out and the power supplies verified.
not sure what happned here but I had two replies from you, one for a Beogram8002 repair post....not mine (sorry)?
and one for the current Beomaster 8000 dilema.
Allow a very brief recap of events:
it started with my first 240V BM800 unit, not getting the volume going plus some cross-over issues switching between FM, TP1/TP2.
after I had done a complete recap and trimmer replacements where appropriate (excl the big 4 caps).
it followed with another 240V BM8000 unit, earmarkd as a parts donor - it finally arrived so I could perhaps use associated parts for the
volume setting (AD7110 chips) and cross-over issue (AD10/278 chips).
in the meantime I discovered the speaker switches on the original project unit were faulty- replacements are on their way - perhaps the solution to the
volume issue ?
a word about that donor unit:
It turned out it had a complete recap job done incl neccessary trimmer replacements - something even the seller wasn’t aware of as he never got around
doing work on it. Now, that BM seems almost too nice to rip apart for parts.
it has the obvious issue that its start-up relays do not engage ? All voltage regulators are fine (15V, -15V, 5V), all associated transistors have been tested
off-board. All critical connector pins have been reflown, pins and plugs cleaned, even the two 2MHz crystals have been replaced (Beolover suggestion)
so, I am ‘torn between two lovers’ here.....in a nut shell : stuck in my tracks with both units right now !đĄđĄ
once I have the speaker switches replaced I shall report back.
I would inspect the work that was done and continue testing the new unit then. Perhaps one of the startup relays have gone bad. I had to replace a couple before.