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 working on a BG6000 Type 5502 and can't seem to control the carriage - it races towards the spindle
without automatic return - even activating '>' has no impact !
looking at the circuit diagram / motor control / there is a table showing various voltages for ON, OFF < and >
I can verify the right column assoiated to MB but not the left one, associated to MR, hence the carriage shows no reaction to return at the centre or when '>' is activated.
I get about 23V on the main rail but the emitter of 1TR25 is not going down to the required 13.5V - instead it remain at about 23V.
what am I doing wrong or what did I overlook ??
can somebody help ??
many thanks - ALF
My bet is one or more shorted transistors in the H-bridge.
Martin
H-bridge is not a term I am familiar with ??
You didn't refer to the Wien-bridge ???
Cheers - ALF
Got it !!
Very specific -in this case you obviously refer to 1TR24, 25, 27, 26 and 1TR29, 28, 30, 31
Correct ??!!
I shall check those set of transistors again - some I did replace, using BC337 instead of BC237 - none at hand but same type.
ALF
Just reporting back:
Checked all transistors in the h-bridge - all fine - the previous owner put one pnp transistor in where a npn was required !
Not sure what is going on here, as now the < works fine but the carriage wont engage in reverse with >>off nor > ????
When activating <<on the carriage wont move, servo wont engage either ???
I checked transistors 1TR18, 19, 20, 21, all tested ok (off board).
I can move the carriage forward engaging ‘<‘ till it gets to the center, then switches off
But does not automatically return to its resting position.
Surely god and the experts know what is wrong here - I hit a brick wall !
Any good suggestions are more than welcome :-):-)
Cheers, ALF
Spent enough time on the old table and decided to use some of its components as spare parts such as the AC motor, arm assembly etc.
Simply can't get it going !!
Is this the same deck you replaced a lot of "tin-can" transistors and whatnot in?
No Martin,
You refer to the 'smoking resistor' :-):-):-) that table works fine after you pointed me to a
Small other problem.
This one was sold as a BG6000 with ''a small problem, probably an easy fix'' !!
First discovery was the CD4-preamp board was missing, controlboard in pieces, wrong small decking-plate, bent sliding rods and carriage-spindle and carriage not moving,
Dead LED at the foto-resistor.......
Carriage rods and spindle incl motor has been re-adjusted, moving freely.
Replaced LED, main drive motor spins when <<on is pressed but carriage does not move.
If manually moved passed the first switch on board4 I can move the carriage via. '<‘ key
Untill it reaches the center-position and the second switch on board4 klicks....but no
Automatic return to its resting position.
I tested off-board almost every transistor that sshould have a say in that without finding a bad one. I replaced various big resistors, which were out of spec.
I also noticed that 1R1 is getting quite warm without turning on the table ???
Needles to say I checked numerous voltages as well............
All up, hours spent without - can't get it going !
Heers
Qick up-date:
Replaced 1D21, now the carriage is moving to the record and arm lowers when '<<on' is pressed.
Still can not find the cause of carriage not reacting to '>>off' nor. '>‘ nor automatic return to resting position ?
Let's briefly resume:
Pressing '33' should be for record wiping - not working
Pressing '<<on' carriage moves to start of record and arm lowers if record is present,
In case of no record carriage moves right across without lowering arm until ES is activated but does not return to resting position.
Pressing '>>off' or ' > ' shows no return or movement of the carriage.
Muting circuit is missing as CD4-preamp board is missing - no relay present on main board.
There must be another problem-component on the main board ?!!!
Thanks - ALF
Seems like the famous needle in a hay stack !
I absolutely ran out of ideas after checking almost every transistor off the board,
Every diode in the electronic switch and motor-control circuit.
Perhaps someone with another lead or simply continue the lottery-search ?!
I am listening ......... even to silence :-)
Happy to report the needle has been found
Now off to eliminate the slight hum and we are in business