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Beomaster 2000 Typ 2801 Restoration or Parts ??

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ALF
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ALF posted on Sat, Apr 15 2017 4:37 AM

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 !


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ALF
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ALF replied on Sat, Apr 15 2017 5:15 AM

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

solderon29
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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

 

Steffen
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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)...

ALF
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ALF replied on Thu, Apr 20 2017 12:59 AM

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

solderon29
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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.

Regards,

Nick

ALF
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ALF replied on Sun, Apr 23 2017 4:37 PM

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.

cheers

ALF

solderon29
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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

Regards,

Nick

ALF
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ALF replied on Tue, Apr 25 2017 1:01 PM

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 !

cheers

ALF

ALF
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ALF replied on Wed, Apr 26 2017 9:16 AM

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

Dillen
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Dillen replied on Wed, Apr 26 2017 9:30 AM

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

ALF
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ALF replied on Wed, Apr 26 2017 1:44 PM

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.

ALF

Dillen
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Dillen replied on Wed, Apr 26 2017 2:23 PM

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 to
the 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

solderon29
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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?

Regards,

Nick

Dillen
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Dillen replied on Wed, Apr 26 2017 8:37 PM

Yes, B&Os tuners are generally very good. Actually so good, that even with certain faults they can still be good
enough 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.

Martin

ALF
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ALF replied on Fri, Apr 28 2017 10:48 AM

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.

cheers

ALF

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