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
Hi everyone,
a new "treasure" has arrived....35 Euros and the big question is:
restoring or keeping it for parts ? I have done a foto shoot as a first impression, so bear with me there will
be a number of pics uploaded !
this was obviously the top-side - woodwork is intact, just needs a bit of oil to freshen up.
what is not so nice are the loose buttons......
a better view of those damn buttons !
here they are bottoms up - I wonder what is in their grooves ? is this original left-overs from their attachment fitting ??
moving to the far top right - all seems fine, no major scratches and complete with the pre-set cover
having a look under the pre-set cover and a play with the pre-set trimmers...the first discovered problem: only two are adjustable, the rest wont move
with their finger wheel turing but not the attached axle :-((
and here close up the two center ones as an example....have to take them off the board an probably re-glue the finger wheel ?!!
lifting up that pre-set box shows what years of garage storing can do...shame the cleaning lady is on vacation !!
moving on inside - have a look at the sliding rod for the dial arm !! cleaning, lube-job.....the dial cord simply slips through without
moving the dial arm assembly on its rod !
same issue from a different angle !
corrosion where its due....but here ? totally unneccessary !! the next issue, a broken wire for the dial arm illumination ??
some good news, the dial cord is still in one piece and attached :-))
let's have a couple of views on various boards and enjoy the incredible dust-cover !!!
not to mention those replaced power transistors, which are obviously not the original ones ?!?!?!
and here the right side !
a final one (have more if you curious ?) to enjoy
The BIG remaining question is:
is it worth restoring or keeping it for parts ?
I can not go back to the original MJ3001/2501 power transistors as the collector rods are missing, which begs the question how much performance/sound impact that has ?
obviously the usual capacitor replacement job, fixing the loose buttons issue - thank god they are at least present !!
and fixing the pre-set trimmers ???
any suggestions or comments you want to share with me before I recall the cleaning lady or book a flight to follow her ?!
cheers
ALF
wh
This could become a "hair shirt" type of restoration?
These Beomaster's come from a sad period in B&O history,where the company were hopelessly trying to compete with far superior product from the far east.
All the usual B&O key's are there of course,innovation,styling and sound quality,but the build was rather flimsy to say the least.
The operating buttons were simply glued in place with epoxy,and usually flew off due to shock from the spring loaded switching mechanism.
We glued them back,but it was quite tricky to get them all lined up as the design demanded.The wide use too,of fragile plastic moulding's means a risk of vital locating lug's snapping off and wotnot
It looks as though your Beomaster is "original",ie very little work has been done over the year's.They look like the correct output transistors too.
You will need to recap of course,and replace oxidised preset's etc.The complex function selector switches will be noisy and intermittent due to oxidatiuon too, I expect.
If you have time and patience,go for it.You know the reward if you have restored other B&O?
Regards,
Nick
ALF: this was obviously the top-side - woodwork is intact, just needs a bit of oil to freshen up. what is not so nice are the loose buttons......
The Loose buttons will be the easiest part of your repair on this beauty. They were simply glued to the switches underneath. So simply glue them Again - the tricky part, however is to align them, so that they are flush to the surface...
(edit: Oh, I just saw that "solderon29" already mentioned that)...
Thank you -- you might be quite right here......I will leave that for last !
some progress can be reported:
pre-set trimmers have been restored to working condition, all finger wheels were loose.
Dial and ON lights shine again as well as the dial rider, meaning the big tuning wheel can scan the stations again.
idle current has been reset to 10mV
first road block:
the tuner only functions is Mono ! Whether this is the IF signal too low ??
I checked all associated voltages on the fm board according to the circuit diagram but no Stereo light and no tuning indicator lights either ??
in the meantime I shall study the tuner description in the SM again but perhaps someone has any suggestions or clues to provide ?
and yes, I did check the bulbs - they all seem fine ?!
There is also the question about a power transistor change in the past - perhaps Martin would know ?
the manual has MJ2501/3001 listed as the original ones but fitted are TIP141 and 146 ??
cheers - ALF
I think the output transistors are probably correct,and a production alternative to MJ2501/3001.They are a similar beast to the ones in the spec electrically,but there may be changes to other components on the board to accommodate them.You may be making unnecessary work for yourself by replacing them?
It would be prudent to replace the idling current presets of course ,as they are notorious for causing output stage instability and "spontaneous combustion".The caps as you know,are a must to replace too.
I don't remember having much trouble with the tuner section.The "usual suspects" of course are tantalum bead capacitors,particularly in the stereo decoder,or anything that will reduce the if bandwidth etc.
We used to glue the buttons back on,after clearing all residue of the original epoxy away.You can make spacers from thin card,to space the buttons apart from each other by the correct distance.Then use slow curing Araldite to glue them on.Use a couple of weighted small square dowels across the buttons to prevent fore/aft rocking as they set,then leave overnight to set.
Fiddly,but rewarding to get the buttons all lined up.
You've made a good start on it sir.
Hello nick,
thank you for your encourageing words......well some progress has been made:
loose buttons are fixed - i noticed some of the other buttons must have been refitted in the past, meaning it is not as perfect as i would have loved but will not " disturb" the assembly.
caps have been replaced on board no.2, the FM section as well as on the preamp and output board.
as a matter of interest, almost all tantalum bead caps were pretty much within spec while the big ones - yellow and brown-red - were way out of spec !!
so, the FM bord had all caps replaced, the preamp and output board only the big ones.
both idle-current trimmers have been replaced with modern Piher trimmers.
i also replaced 2IC 2 and 3 with MPSA 13 transistors, however that did not change nor improved the tuning indicator light situation:
ON, Stereo and Tuning indicator bulbs as well as the Dial bulb are "silent" again ! ON and dial light was working for a short while previously?!
that is odd - the SM gives some explanation on the tuner function which I can not quite work out ?!
the FM signal definitely comes in Mono only ??
clues are badly needed.
as for changing the output power transistors, you are absolutely right - it looks as there was a change in the running production from MJ to TIP darlingtons?
i certainly won't engage in a mad replacement job as the current ones work fine - actually quite powerful sound !
but that tuner / light bulb matter needs to be taken care of.
as always, I sincerely appreciate any support.
Make sure that you have fitted the capacitors in the correct polarity,it's easy to get those pesky "tants" in the wrong way round!!! They are good capacitors in that they are long lived and stable,but they can cause odd intermittent problems,and so they figure on my list of "the usual suspects".
When you say it's mono fm,do you mean only one channel working,or both working but not in stereo?
Is the quality good,and does the interstation muting work ok?
You may have a faulty stereo decoder chip (MC1310)
Check supplies of course,and you may be able to "prod" the decoder into life using freezer spray.
As to the lamps,the on,dial and stereo have a common supply,but zener 4D1 may be causing problems for the dial and on lamps.The stereo lamp of course won't work if there is no stereo signal.
The values of the lamps are crucial (12v 30mA) I think the stereo one is different,but it shouldn't influence the other's
Ok, here is what happened in the meantime:
all caps have been checked for correct polarity - all fine
both channels are working but the FM signal is in mono with quite good quality
there is a Stereo decoder chip on ebay which I may buy but will try the suggested freezer spray first, which hopefully will deliver some answers.
I checked all voltages as per circuit diagram at IC4 = MC1310 PQ, all fine except pin6, which only delivered about 130mV instead of 1V - that is going
to IL3 and IL4
also the emitter voltage at 2TR5 is about 560mV instead of 5.4V (=TP7)
2TR5 is connected via 2TR4 to pin10 of IC1 = TCA420A......!
I will check 4D1 to be sure but somehow don't quite believe that isncausingbthe issue with the dial and ON light ?.
talk after the freezer treatment of the stereo decoder !
Sadly no luck with the freezer spray treatment 😪 On the stereo decoder chip?!
I decided to replace that chip anyway with a NOS motorola, just got to wait for delivery.
just to clarify something:
there was no Stereo FM signal before the recapping of the tuner board, but sound on both channels in mono.
ALF: there was no Stereo FM signal before the recapping of the tuner board, but sound on both channels in mono.
IF signal too weak.Typically because of bad antenna, weak frontend, faulty AGC circuit or misaligned IF stages.The latter rarely happens unless the "phantom" messed with them.A too weak IF signal will also leave the two tuning discriminator lights unlit.
Martin
Yes, if IF signal is too weak and the output from IC4 will be mono !
what surprises me though is the fact that the tuner pulls in all stations quite well with a short piece od wire as antenna ?!
does that really point to a weak front-end ?
also, the IF signal is fed through 2TR1 for amplification.....I am not sure about the typical voltages at C or E of TR1 ?
perhaps that transistor is on the weak side ??
the two indicator lights left unlit by a weak IF is at last explaining what could be the issue with those bulbs ! Which IC is involved with the AGC circuit?
Anyhow, thanks for these pointers.
You should have apprx 3V on the emitter of 2TR1.There's no IC associated with the AGC. The signal is taken from 2TR1 and fed back tothe FETs as a negative voltage.Does AGC react at all?Did you replace or adjust any of the trimmers in the tuner?Have you checked the supply voltage to the tuner for ripple? D8 is a known troublemaker - so is C24.Martin
I'm still suspicious of the decoder chip(MC1310)and the very low voltage at pin 6 is significant.This should be at 9v for mono,ie,no stereo signal present,then drop to 1 volt for strereo and of course draw current through the mpx lamp to illuminate it.
I assume that the mpx bulb is the correct one and ok?If you short pin 6 of the decoder chip to chassis,the lamp should light.If it doesn't-eureka!
As I mentioned earlier,the lamp values are crucial.As Martin say's,particularly the tuning lamps depend upon specific currents to function properly.
I agree with you about the general reception,it seems that "front end" and if stages are functioning normally.If the interstation muting works too,ie there is no loud hiss when tuning between stations,it would further suggest all is well there.The muting can be switched off,the switch is with the tuning preset's.
You tend to need a strong signal for the stereo decoder to kick in,but generally,B&O tuners are quite sensitive,and will work happily with the B&O "rabbit ear" antenna'a or similar.Unless you are way out in the "bush",you must have strong local radio stations to use?
I think you nearly have it sorted sir,and no need of the hair shirt yet?
Yes, B&Os tuners are generally very good. Actually so good, that even with certain faults they can still be goodenough to doubt them being at fault at all.When you have done a few, you will know what to expect and what's normal in your area.
The AGC feedback line is a good place to measure in cases of possible IF- or general sensitivity problems.The signal should be very active - several volts up and down - when tuning past a strong station.Beomaster 2000 has no S-meter, but a DC-voltmeter to the AGC line will function pretty much the same.
Eureka 👿
The lamp does not light up !
I have a new decoder chip coming - can't do much damage.
wheather the chip has issues we'll see.
Emiiter of 2TR1 shows about 3.5V.
no trimmers have been replaced except the idle current adjustment trimmers.
D8 is on order and C24 has been replaced with a brand new 470uF/50V cap only a week ago.
Pin 6 of the stereo decoder should have 9V/1V instead shows around 10mV.
voltage at R22 - gateway to AGC - shows about 21V and does not change.
regards
R22 is not associated with the AGC line.Don't mix up AFC and AGC.
Pin 6 of the stereo decoder is an open-collector output and its low perhaps because somethingin its pull-up is missing (f.e. a broken dial or MPX lamp).Do you have the MPX pilot on pin 10 (TP9)?
Apologies, quite right - various distractions of house jobs are not good for that kind of "past time"
looking at 2R9 which is the one Iassociated with ACG is where I am getting a bouncing signal while scanning the stations.
pin10 - TP9 - shows 2.98V
I checked the MPX bulb for open circuit but get a resistance reading, bearing the question whether this would be conclusive enough ?
did not yet check the dial bulb, seems tricky to recover ?
Cheers
The dial lamp sits in the travelling pointer.Its pins and solder points are usually easy to access.
D8 has been replaced as well as C24.
I also replaced the stereo decoder chip and IF amplifier chip.
Still no lights are illuminated - seems like I have to replace all light bulbs ?!
still waiting to order the new lot of BG4000 belts plus of course those light bulb replacements as discussed.....😳
Well,
after spending some more time with the BM2000 I had to discover a couple of things
related to the famous 'phantom' !!
someone installed a LED as dial light, obviously in absence of the original replacement bulb - the bulb fitting
in the runner is also broken thanks to that phantom !
I was - as mentioned earlier - going to purchase a set of the correct bulbs together with those new BG4000 belts.......
as interims solution I fitted a set of 12V-40mA bulbs instead of the correct 12V-30mA ones just to check whether stereo reception is possible !
yes it is, but the alignment of the FM section obviously had been tempered with by ???
after fitting a new decoder and IF amp chip I have stereo reception.......but only after some "blind" adjustments in absence of a sweep generator.
some basic adjustments could still be made.
the tuning indicator bulbs perform but seem very dim and the stereo bulb still does not light up ?
i do not want to mess around any further with the alignment procedure as the BM sounds quite remarkable as it stands.
a sweep generator is on the wish list, but perhaps there is an alternative adjustment procedure I could try or is this wishful thinking ?
anyhow, I am patiently waiting to get my order in for those bulbs (plus the BG4000 belts 😳)