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 all,
New to the forum, looks great!
I have a mint looking Beomaster 4400 that I'm slowly bringing back to life. The previous owner had hacked in another DIN cable (probably to connect it to an external equaliser). In the process of using it, it seems he has blown up the pre-drivers. I already fixed this by removing his hack, and replacing those transistors (5TR112 - 5TR212).
Now the only problem is FM reception. I get white noise. And that's about it...What I already checked:
-Supply voltage is good (15V) -> even on a scope, no oscillation/ripple to be seen.-2TR1 looks OK (diode check base to emitter/collector 0,7V in both cases)-Moving the dial left and right, moves the tuning voltage up and down - I see that at 1R1/1R5 -1TR2; I don't know, measured it with the diode check: 0,9V/1,0V. So it measures like it should, although pretty high. Is this normal for a BF255? Don't have ant spares around.
Anyone can give me some pointers? I have some experience with amps, but FM isn't up my alley yet ;)
I suspect the TIS88A's (1TR3 and 1TR4). Getting 14.3 volt at the drain of TR3; 4V at the source; but only 0,4V at the source of TR4; instead of 0,7 in the schematics.
Anyone can chime in on these? Do they frequently fail?
Well, it was 1TR2 all along. Measured high as I was thinking in the first place. Replaced it with a fresh (NOS) Siemens BF255. Great reception!
While I cannot help you on a component level these are a great system and really with your time and effort.
I always enjoy mine.
Keep up the good work !
Yes, they are pretty good. Did extensive work on this one, as it's optically in mint condition.
There's some oxidation on some of the more used knobs, that will be taken care of with a respray. I've got a new preset-window coming in, in the next few days.
She'll be like new! :) ********* - I like fixing these as projects )
***** Edited by moderator DillenWe kindly ask members to upgrade membership level to minimum silver to place wanted/sales ads.
Sorry admin - had no intention of s****** here :) just wanted to post the info in case someone runs into the same issue!
Here's the Beomaster 4400, after respraying the switches and a full teardown and service :)
Very nice, though I do spot an important part missing...
Martin
You don't say? I recently ordered one on ebay from.. well... you haha
Much better
I agree.
Very nice.
I use mine several hours a day with M70 speakers and those three are excellent hi-fi company... with a MacBook Pro!
Beolab 5000 apart, my favourite B&O amplifier, period.
Jacques
Stunning pictures, that has to be one of the nicest 4400s I have seen.
Congrats and enjoy!
Ben
Just a further heads-up. I decided to replace 5TR112/113 and 5TR212/213 (Both input differential pairs) to lower the DC Offset even further. I used my curve tracer to match 2 pairs of BC546B. I noticed that B&O marks these in the datasheet as "Specially Selected Specimen" - maybe that's what B&O did in the days.
Before the matched pairs, I had 36mV/32mV offset. Not bad, but not great either. I now have 1mV/1.8mV offset. Worth it!
I know - a little bit late.
But how on earth are the sliders so clean / transparent?
Most of my collection with vertical sliders e.g. BM / BL / BC 3000, 4000, 4400, 5000, 1700, 3500 etc. does suffer from bad looking sliders .
Perhaps (I'm sure) during a lifetime with nicotine air.......
Perhaps, Martin, you can start up a fabrication of them like the preset covers, which indeed look amazing
/Leif
Patience... ;-)
I guess the unit didn't belong to a smoker (almost squeaky clean inside, except for some dust) and it probably didn't sit in the sun :)
Would be awesome if Martin made these indeed, as they are a bit fragile and really make or break the looks of a unit! :)