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
greetings all,
I am hanging over one of my BG4000, trying to adjust the Servo.......for hours........
done all the usual tricks incl a new servo-motor belt, but it won't comply !!
checked 1D7/13 - tested fine, if 0R3/4 -which are vintage OPR61 resistors- are faulty the question would be
'where to get those or possible replacements' ??
also visually inspected 1TR31/30/29/28 showing visible dark brown burn-marks on the board.
I have two matched pairs of NTE129MCP transistors - would it work to use these two pairs to replace the 4
old existing BC types BC142/143/144 without causing a problem ?
as always, very happy to receive your comments before I cause "further damage" :-)
ALF
If you need to replace the BC... transistors, I suggest you stay with the BC types.Not that it matters that much in this application, but the NTEs are notoriously noisy.
But - what are the exact symptoms?
Martin
Thanks for your input, but are these NTEs humming to the record's content ???
Just kidding, these matched pairs cost a small fortune that is why I am surprised to hear about
Their short-commings ! It was actually recommended by Menahem to change the old BC types as they
Getting quite hot to these matched NTE pairs.....that is the story behind it.
Detecting dark burn-marks on any board just makes me feel uneasy, that is why the idea for
Replacing the BC types came up.
After going through the adjustment procedure the servo was either going backwards, if forward then far
To quick - no stable setting between seemed achieveable - to make matters worse just before entering
The runout-groove it would not go any further.........
After checking various switches and spring-settings......nothing seemed to get the arm to its
End-of-record lift-off position.
As per SM I checked the diodes directly involved, the set-up of the solanoid switches but not yet the two ORP61 resistors !
After another study of one of 'sonavor's posts I revisited the adjustment procedure and started from scratch !!
Now it is working again :-):-)
The only thing I am not entirely happy about is the pick-up arm during play
Could be slightly more parallel to the detector arm !
There are no electronics in the signal path of the Beogram 4000 so no component will have any direct influence on the sound reproduction.They are all there merely to handle the operation of the deck.
NTE transistors have started to become noisy, It seems to be a matter of them aging.I have had several cases, mainly where they were used in preamplifers and the likes, where theystarted to make noise, not exactly hum, more like a faint crackle, a little amount of white noise and/or an occasional pop.It's rare to see BC types do that.I see no reason to fit NTEs when original types are still available and whenever I find NTEs in any B&O coming in here, I like toreplace them with exactly that.It's not particularly important when using them as DC drivers as they are in the Beogram 4000 though, and I'm sure they'll be fine.Whether you fit NTE or BC types, they see the same job and they handle the same voltage and current sowill dissipate the same amount of energy in the form of heat.The darker board areas are normal and unless completely black shouldn't be cause for much concern.You could choose to fit the new transistors lifted a mm or so above the board foradded air circulation, but the transistors will be fine even if hotter than you'd like to touch.No transistors in Beogram 4000 need to be matched pairs.Martin
Thank you for your thoughts Martin - I was just going to add a note to my last post, asking the question
whether it is really wise or neccessary to change parts based on suspicion and darker marks on a board
When everything is still working !?? I guess 'NO' !
Just to be prepared, I did buy some new BC types, acting on your advice though.
And yes, I am aware those parts do have no say in sound-reproduction:-)
What worries me however are these old orange caps on the main board, some of them tested
way out of spec!
Cheers
The orange radial Roederstein (ROE) caps of the early 1970s can be replaced on sight. If not already bad, most will be marginal by now.Red ones of the same type (of the late 1970s and early 1980s) will be more or less the same.Curiously, the majority of the older grey types (of the 1960s) from the same producer is still doing fine.