Beomaster 4400 - bringing it back to life

16 replies
W(
Offline
Wirehead (archived2)
Bronze
Posted March 9, 2016 at 18:19 GMT
#2204231

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 ;)

W(
Offline
Wirehead (archived2)
Bronze
Posted March 9, 2016 at 23:21 GMT
#2204232

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?

W(
Offline
Wirehead (archived2)
Bronze
Posted March 15, 2016 at 11:29 GMT
#2204233

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!

VA
Online
Valve1
Gold
Posted March 15, 2016 at 11:45 GMT
#2204234

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 !

My B&O Icons:

BeoCenter-9500.png BeoCenter-9500.png
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Beovision-10.png Beovision-10.png
Beotime.png Beotime.png
Beosound-9000.png Beosound-9000.png
Beomaster.png Beomaster.png
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W(
Offline
Wirehead (archived2)
Bronze
Posted March 15, 2016 at 17:48 GMT
#2204235

Yes, they are pretty good. Did extensive work on this one, as it's optically in mint condition.

 

  • Recapped where needed with Panasonic EB series (105°C - 10 000 hours) / Philips. Gone are the leaky Roederstein caps.
  • Replaced the LM7815 voltage regulator, as the 15V rail was measuring a little low
  • Calibrated the tuning voltage
  • Realigned the tuner
  • Desoldered all output transistors, measured every single one of them and remounted them with new thermal grease
  • Replaced the pre-driver transistors
  • Replaced the BIAS-trimpots with closed ones
  • Cleaned the front-panel slider-pots with IPA

 

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 Dillen
We kindly ask members to upgrade membership level to minimum silver to place wanted/sales ads.

W(
Offline
Wirehead (archived2)
Bronze
Posted March 24, 2016 at 14:38 GMT
#2204236

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 :) 👍

DI
Offline
Dillen
BronzeModeratorFounder
Posted March 24, 2016 at 15:20 GMT
#2204237

Very nice, though I do spot an important part missing...  👍

Martin

W(
Offline
Wirehead (archived2)
Bronze
Posted March 24, 2016 at 15:24 GMT
#2204238

You don't say? 😕 I recently ordered one on ebay from.. well... you 😁 haha 

W(
Offline
Wirehead (archived2)
Bronze
Posted April 16, 2016 at 10:49 GMT
#2204239

Much better 🤒

DI
Offline
Dillen
BronzeModeratorFounder
Posted April 16, 2016 at 12:26 GMT
#2204240

I agree. 🙂

Martin

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