BeoGram 4000 Repair Restoration

73 replies
...
YA
Offline
yachadm
Bronze
Posted August 31, 2011 at 15:34 GMT
#1760655

Hi all,

I just picked up a throwaway Beogram 4000. Not in the best cosmetic shape - cracked acrylic cover, but the aluminium fascia isn't bad - should clean up nicely. It is not mechanically operational at all, and the MMC20S is minus the cantilever.

I've restored about 15 of the BG4002's and BG6000's, but this is the first time I've ever seen THE original tangential TT.

I've cleaned the interior, and I'll be starting on the capacitors, potis and replacing the OA90's with AA143 diodes. The usual degrease and reoiling ala the BG4002 series, and then I'll try a power on (via a series lamp) and see what happens - more to come.

Here's the interior.

Menahem

Location: Jerusalem

My B&O Icons:

Beoremote-Beo4.png Beoremote-Beo4.png
Beovox.png Beovox.png
Beomaster.png Beomaster.png
Beogram-400x.png Beogram-400x.png
Electronics Technician in Jerusalem Israel. B&O fan for over 50 years.
hemenex
Offline
hemenex
BronzeFounder
Posted August 31, 2011 at 15:44 GMT
#1760656

good gracious...

that's a box full of electrolytics spreaded all over 😉

RI
Offline
richhaffner
Bronze
Posted August 31, 2011 at 21:48 GMT
#1760657

Best of luck from an interested reader!

Evan
Offline
Evan
Gold
Posted August 31, 2011 at 23:24 GMT
#1760658

hemenex wrote:
that's a box full of electrolytics spreaded all over

What he said!!

Have fun with this, looks like there's plenty to be had! 😎

Location: San Francisco

I'm an automotive audio and acoustic engineer. I design loudspeakers and full sound systems for new automobiles. I also dabble with studio, consumer and pro audio projects from time to time.
mexking
Offline
mexking
Bronze
Posted September 1, 2011 at 00:13 GMT
#1760659

OH OH expensive 3000 caps😕

Location: Mexico city

Retired
Printing machine technician
Restored various 1960-70 items
Rock and Roll music
Collecting Vinyl
Restored Jukebox Wurlitzer 1050
SH
Offline
Søren Hammer
Bronze
Posted September 1, 2011 at 02:55 GMT
#1760660

That is indeed one big mouthful 😎

hemenex
Offline
hemenex
BronzeFounder
Posted September 1, 2011 at 03:49 GMT
#1760661

Søren Mexico wrote:

OH OH expensive 3000 caps😕

Probably not expensive but surely in a strange dimension - most of the available ones are much wider in diameter 🙁

But lookin' at Menahem's BM3400 there's a very slim nichicon 1000/50 so I'm sure he'll find suitable substitutes.

   Gunther

 

YA
Offline
yachadm
Bronze
Posted September 1, 2011 at 04:44 GMT
#1760662

Yes, that extra 1000uF cap boosts the standard 470uF decoupling cap on the Bridge rectifier. Because I dumped the original B80C, and substituted my own homebrew 4x Schottky bridge, I was no longer limited to the maximum bypass capacitance of the original B80C bridge. So now, with about 1500uF bypass capacitance, the ripple is almost nothing. Of course, the improvement in sound is quite audible.

I'll do the same Schottky upgrade thing on this BG4000, and here, I'll use 3900uF 50V, 25mm diameter, but obviously the length will be much less.

Menahem

Location: Jerusalem

My B&O Icons:

Beoremote-Beo4.png Beoremote-Beo4.png
Beovox.png Beovox.png
Beomaster.png Beomaster.png
Beogram-400x.png Beogram-400x.png
Electronics Technician in Jerusalem Israel. B&O fan for over 50 years.
C(
Offline
chartz (archived)
Bronze
Posted September 1, 2011 at 07:12 GMT
#1760663

Menahem,

I shall be watching this attentively (and of course provide my help should you need it!), since I also restored a Beogram 4000 not so long ago. I think I know it (and its caveats) inside out!

Cheers,

YA
Offline
yachadm
Bronze
Posted September 1, 2011 at 12:52 GMT
#1760664

OK, I've done enough of the bad components to start troubleshooting.

I have some problems with the keyboard contact switches - the flappers of < and V are not working - I'll have to pull apart the keyboard, and adjust.

 

Jacques - I hope you made good notes when you did yours ;-)

1. What DC voltages (reference to GND) did you get at the BCE of both 0TR1 and 2TR6 - very easy - it's the voltages on the big capacitors and the zeners? I know what the SM shows - I want real-world voltages.

2. What are the actual 1VR1 to 1VR6 installed on your PCB - mine do not match the SM values, and I want to know if I can install the minmum values possible to get more precision adjustments?

3. What is the DC voltage on the tonarm lamp sensor - I show 6.4Volts - lamp burnt out? I want to put in an LED, and discard the poti. See the picture - red arrow is the +ve supply to the lamp.

 

Location: Jerusalem

My B&O Icons:

Beoremote-Beo4.png Beoremote-Beo4.png
Beovox.png Beovox.png
Beomaster.png Beomaster.png
Beogram-400x.png Beogram-400x.png
Electronics Technician in Jerusalem Israel. B&O fan for over 50 years.
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