T5525

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Martin

Thanks to Martin, who sent me the schematic diagram, my 4004 is slowly improving 🙂

I noticed that the arm transport was slow and impossible to align with the trimmers, so I replaced all 4 transistors that drive the arm motor.

Now the transport is smooth and steady, and the automatic start seems to work too, although there are still random errors, especially with automatic stop: most of the times, the arm raises and returns way before the end of the record. But sometimes it plays the record from start to end… maybe it's a matter of taste 😉

Time to stop and wait for the new belt. I'm getting closer…

Thanks again to Martin and Keith for their help. 

Finally the new belt arrived (thanks Martin) and now everything seems to work…

I thoroughly cleaned the arm assembly and I've been able to play some records from start to end. I keep my finger crossed while I'm writing this… not an easy task by the way😕

I still need some time to check all the alignments, but I'm positive I'm almost there. Yay!

Hi guys. It's been a long time... I had a lot of work and I didn't find much time for my Beogram: I had to fix some of my musical instrument first. But last week I took it off the shelf and put my full attention on it - or should I write her? 🙂

I couldn't get rid of a random fault: sometimes the arm rises up during play and returns home. I had the impression that it happens in certain spots, corresponding at 12" and 7" record diameter, but at times the whole record plays without stopping. I HATE random faults... 😭

Reading service manuals and tech descriptions, I focused on LED 4D1 and photo-transistor 4IC1. After checking out solder joints on transistors 1TR16, 1TR17 and 1TR18 and cleaning the ruler, I removed the LED and found a broken leg... Of course I don't know if I broke it or it was already, but I believe it was a good idea trying to replace it, so no regrets 😕

On Menahem's PDF about 4002 restoration I found this quote:

 I replaced the 24V 25mA lamp (IL1) with an opaque white medium-intensity 3V LED. This light from this LED is highly directional, and much more intense than the original lamp. So the Photo-transistor, on my unit a Motorola 2N5779, should be able to sense the light more precisely now.

Oh, I got another important question for you guys.

The sound of my MMC20EN is pretty dark... no high end at all. Could it be a bad symptom ?

I'm using my old Marantz 1040 for testing, and I know the RIAA preamp is fairly cheap, but I tried another amp - a '90s Onkyo - without noticing any difference. Of course I'll wait until the restoration job is complete, then I'll connect the BG4004 to my Yamaha preamp and I'll run some A/B tests with my Thorens/Shure couple. But I feel something's missing above 8000 Khz or so... Such a pity I don't have a frequencies test record anymore 🙁

In any case, last night I spotted on eBay this pair: BG8000 & BC8000 for 250 euros. Needless to say, I contacted the seller and I'm waiting for his mail. Guess I've been severely infected by the B&O collector's disease 😁

Finally I've made it. It works. It's been a long, hard battle but I won.

Replacing the broken LED with a new one fixed the random thing... the arm didn't lower any more 🙁

I knew for sure there was some bad contact somewhere on the main board, but it was hard to find. Trouble was, I had to take off the plates and the belt every time: then I thought about the "extender boards" I was using back in the studio days to fix mixers and tape recorders, and I got the idea... Login to view image

As you can see, I removed all boards from the chassis. I had to "extend" only the motor and the arm board connectors: the other plugs were long enough to reach the board without extensions.

Then I was ready to check the main board... It took a couple of hours, but finally I got lucky, hitting the weak spot: a bad contact on R62, in parallel with C28, where the low pulse is sent to the electronic switch. When I heard the solenoid "click" I couldn't believe it... 😂

I played a couple of records without problems, then I put everything back in place and I started listening to my old LPs...

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Time to sleep now: tomorrow I'll check the mechanical adjustments.

Many thanks to Martin-DIllen, for the schematic diagrams, the service manual addendum and of course the belt.

Good job and thank you for posting, The follow ups often are missing. Lets "hear" how it sounds tomorrow

Perfectly possible that 4D1 was an IR led. It was on model that I once had.

Søren Mexico wrote:

Good job and thank you for posting, The follow ups often are missing. Lets "hear" how it sounds tomorrow

You can hear it and watch it downloading a short movie from this link

https://dl.dropboxusercontent.com/u/793661/beogram2.m4v

Actually the lab is my favorite listening place: I guess I'll keep it there for a while, though the main hi-fi system is upstairs.

I still believe that the cartridge sounds "too" warm... On certain records it's ok, but sometimes I really miss the high end. I'm a musician and I spent years in recording studios, nevertheless my ears are still working well 🙂