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
am waiting for a Beomaster 8000 to arrive so am following this with interest. Seller claims is working perfectly but we shall see.
Hi,
I wish you luck - one learns a lot about these receivers if it is a ‘to restore unit’ 🤗....but I am not saying yours will be one 🤞
with the help of some of our treasured experts I revived two....one is still in intensive care.
still fighting the volume issue - one of the problems is getting the genuine ICs without wasting time and money on fakes......
Luckily I have another donor unit coming to exchange some boards to see what exactly is playing up....
still chasing some genuine AD7110KN ICs - my second delivery was labelled almost beyond recognition, meaning another delivery of fakes 😡
again I have gone over the tone/filter board, where quite obvious something is not as it should be....
gently!! tapping on P28/29 connectors responds with a horrible crackling noise.
both interconnecting flat cables (P28/29 to uP board) were fine, no wire-break, all showed healthy resistance.
all solder joints look healthy as well - I don’t want to remove the two IC sockets for the AD7110KN pair - that should not have any impact
as both are soldered in perfectly!
anyhow, thank you all for your interest in the problem...
ALF
back to the Tone/Filter board,
something that seemed odd - can't imagine that would be original ?!
first two pictures (solder side & component side) show cut tracks between Stereo and Loudness switch and "fly wireing" between those switches
but why ??
solder side of cut tracks
the next two pictures show a cut track of the Signal switch and the 'fly wireing" from the Signal switch D18/D17
last picture is the component side Signal switch "fly wireing" to D18/R25
can someone shed some light why this would be necessary ?
as always - many thanks
No comments on those rather strange tone/filter mods ???
anyhow, another donor unit arrived and I was keen to swap over its control board to see whether the volume issue has gone away....
NO - it was still the same 🤬
I began to wonder if it would have been too much coincidence that both boards had mal-functioning AD7110 attenuators?
yes, possible but likely ???
question: who would be the next suspect on line here ?
I will move on to the preamp board, however still trying to make sense out this !
as usual, any input would be most appreciated - it feels like I am almost there......😳
No comment on the board someone modified. I couldn't tell you why they did what they did so I would use an original as a guide to put it back right.It is pretty unlikely that the latest unit you received also has faulty volume control ICs. I would try swapping the microcomputer boards (before altering anything). Same goes for the preamplifier board.
John
Hi John,
thanks for your comment - swapped over the uP board as suggested first.....same outcome - that is with the tone/filter board from the “new” donor unit.
will move on to swap the preamp board but want to recap it first - no point running into way out if spec caps (the red Roe ones) and its consequences.
report back as soon as....
So are you saying that in the Beomaster 8000 that has the volume problem you are currently using a different filter & tone control board and a different microcomputer board? If you switch the preamplifier board next I would first try it as is...before changing anything. If the problem persists then start changing the cables between the boards, one at a time, checking the problem after each swap.
More work hours spent 🙄.....
1st swapped the uP board only from the donor unit (uP test passed) - vol issue unchanged.
2nd swapped interconnecting cables - vol issue unchanged.
3rd swapped unrestored preamp board from donor unit - vol issue unchanged.
as said before, unless both tone/filter boards have faulty vol attenuator ICs and both preamp boards are faulty
I almost dare to say the problem could/should be hiding somewhere else in the unit ?!!
but where 😳🤬😳 !!
yes, we discussed the unlikely fact of having two faulty sets of vol attenuator chips I still want to dismiss that option.
both uP boards seem to do their job...is it unreasonable to conclude a problem in the output boards ? But,
I was always under the impression the unit would not switch on if there are problems on the output stages (fault switch !)
Seems we (I) need more brain-power here ...... just got that feeling I am almost there.......
if you guys have any further information call “crime stoppers”
If the problem isn't on the input to the volume control then it must be coming out of the volume control. Are you sure the problem isn't your output amplifier assembly?
Thanks John for caring so much.....
well, the symptoms are similar to my last “rescue mission” - I crank up the volume to 6 on the scale and can hear a very low signal
something you could perhaps experience in a “cross talk situation” when the PH input is selected but idling and a tuner crosstalk signal might
be audible at very high vol setting ?!
so far I was under the impression that the fault switch would engage if the output amp is faulty or wouldn’t it ?!
last time I discovered a wrongly connected cable which did the rescue after discovery - so I checked again and made sure it is not again the trouble source.
coming back to the output amp assembly: I can check whether those wire tabs are incorrectly plugged in, but assume this would be the case
surely the fault switch would kick in ?!
any signal from the preamp would be fed through 4C128/228 to the vol attenuator and via 4P24 to the output stages - both those caps are connected correctly.
I shall get back to investigate the output assemblies........
Are the amps powered up at all?
Martin
Nothing visual obviously wrong on the output boards, however I measured the signal (VDC) at 4P24 pin1 and pin6:
both were about 170mV unchanged when the volume was turned up or down !
which tells me the output boards basically get nothing worth putting out?!
again, is this pointing to faulty vol attenuator ICs ??
Just getting sick of getting fakes from china - wish someone would sell NOS or working used ones ....
It doesn't sound like volume selection or source selection if you have tried more than one of those boards (preamp, filter & tone control, microcomputer).On the output amplifiers though, did you say neither channel does anything? What is the voltage across the emitter resistors (the no-load current measurement)? What is the DC Offset measurement (across the speaker H/L). Did you also say in the past that you disconnected the audio input to the output amplifier assemblies and checked that cable with your scope? I have done that before to measure the THD and frequency response of just the preamp section. The measurement point amplitude will (should) go up and down with the volume control.If that test also fails then I would return to the Beomaster wiring. With multiple boards failing it seems most likely the problem is something common to them all which is the cabling of the Beomaster.
Back to work....
the no-load adjustment is at about 17mV and the DC offset is about 3.1mV which should not pose any danger !
I also swapped over the connecting cable 4P27 to 3P16 without any impact.
again, I looked at the signal at 4P24 pin1 & 6 which remained unchanged during vol increase at around 180mV depending on chassis point.
how much more head-scratching can one endure 🙄😬😬 ?
as things stand I would pass on the output boards as suspects - it is quite clear to me that these boards actually get nothing to work with !
I wish I could get my hands on a pair of reliable attenuator chips in order to either fix the issue and/or exclude those from the suspects list.
to be continued .........
Hi ALF,
I'd go back to basics to see where you lose the signal.
Starting at the obvious, do you have the external filter links in place?
Using the FM as a source do you have an AC signal at R250 on the preamp board? You can used the leg of R250 that is common to R249 as the measurement point and the other leg of R250 as signal ground.
If so, do you have an AC signal at R258? Use the leg that is common with connector P16(5) and the collector of TR203/204.
If so, do you have an AC signal at R236 on the Filter board? You can leave the signal ground at R250 and measure the R236 leg that is common with pin 15 of AD7110.
Regards
Lonnie
Hi Lonnie,
BINGO 🙏🤙🤗
the bloody famous “obvious”.......I can’t believe I missed that one !
yes, volume has been restored - thank you so much.
to be honest, i have never looked at those jumpers as they were on all BM8000 I have had so far.......
now I learnt something new again and get started with the next project......!
thank you to everyone who has tried to help......well and truly a team effort.
good to know one is in great company.
Well done, mystery solved. I agree with you, the people on this group are a fantastic resource and I've learnt a lot from their words of wisdom.
So... please don't keep us in suspense..... what is the next project???
Incredible! Phew!
Jacques
Well,
there is still the BM8000 donor unit........probably another high-speed project ?
Not sure yet how much effort is necessary to bring it back to life....we’ll see
and if, no doubt there will be posts 😁😁 and in between the odd relaxant 🍷🍷