VCR works fine in play and record as long as the head drum gets up to speed
by flicking by finger while the tape is lacing.
So assuming nothing wrong with the bearing , normal free movement when
unpowered.
Sometimes drops out in play or record on hitting ruffled tape so a motor
problem.

VCR is Osaki VCR 34H , no knowledge, so i don't know if correct ps voltages
for a start

3 lines from the TA2620D driver IC to the coils and further ends of each
are joined together but not returned to anywhere so presumably 3 phase.
There are 12 coils from these 3 lines mounted on the iron frame with 12
'poles'
The surrounding magnet rotor part has 8 North poles, 8 South poles.
On pcb 3 hall effect sensors presumably for relative phase monitoring these
magnets and a separate magnet pip on the outside of
the rotor and 1 hall effect sensor for 1 pulse per rev.
But what is the PCB track/coil ? etched on the board under the rotor.
Not connected to anything else on the motor sub-board and just copper track
as far as I can see,
roughly like Beta vcr tape path, one track runs right round circularly and
returns 'circularly' with 24 castellations pattern.
What and how is it sensing or sending anything? and what's its function ?

I have another matching salvaged multimagnet rotor so can eliminate
magnetisation loss as reason

Any tips for 1 or 2 channel scope for monitoring driver IC, does not run hot
and
unpowered 'diode' DVM checks seem reasonable.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

correction - driver IC is TM2620D, no logo

"N Cook" wrote in message
...
VCR works fine in play and record as long as the head drum gets up to
speed
by flicking by finger while the tape is lacing.
So assuming nothing wrong with the bearing , normal free movement when
unpowered.
Sometimes drops out in play or record on hitting ruffled tape so a motor
problem.

VCR is Osaki VCR 34H , no knowledge, so i don't know if correct ps
voltages
for a start

3 lines from the TA2620D driver IC to the coils and further ends of each
are joined together but not returned to anywhere so presumably 3 phase.
There are 12 coils from these 3 lines mounted on the iron frame with 12
'poles'
The surrounding magnet rotor part has 8 North poles, 8 South poles.
On pcb 3 hall effect sensors presumably for relative phase monitoring
these
magnets and a separate magnet pip on the outside of
the rotor and 1 hall effect sensor for 1 pulse per rev.
But what is the PCB track/coil ? etched on the board under the rotor.
Not connected to anything else on the motor sub-board and just copper
track
as far as I can see,
roughly like Beta vcr tape path, one track runs right round circularly and
returns 'circularly' with 24 castellations pattern.
What and how is it sensing or sending anything? and what's its function ?

I have another matching salvaged multimagnet rotor so can eliminate
magnetisation loss as reason

Any tips for 1 or 2 channel scope for monitoring driver IC, does not run
hot
and
unpowered 'diode' DVM checks seem reasonable.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

I'm unfamiliar with that brand, but check capacitors on the stator,
or the circuit that feeds it, as well as the main power supply caps.
Sky.

Could it be the same board (with the mystery traces) is also used for
other model vcr's where the traces are actually used. Or could it be a
kind of ground trace where the intended purpose is not so apparent.

Have you considered the motor driver(drum) maybe partially failed in
that it is not delivering enough current, and in turn drum torque.

Skype_man's suggestion makes sense as well in that the power to the
drum must be clean. Sounds like it will take a bit more
checking and probing. I'll bet the driver passes the diode test since
it at least partially works. It's an interesting problem, keep us
informed of your progress. I had a similar problem years ago. Hard to
remember exactly how I fixed it.

Dennis H.

"distar97" wrote in message
oups.com...
Could it be the same board (with the mystery traces) is also used for
other model vcr's where the traces are actually used. Or could it be a
kind of ground trace where the intended purpose is not so apparent.

Have you considered the motor driver(drum) maybe partially failed in
that it is not delivering enough current, and in turn drum torque.

Skype_man's suggestion makes sense as well in that the power to the
drum must be clean. Sounds like it will take a bit more
checking and probing. I'll bet the driver passes the diode test since
it at least partially works. It's an interesting problem, keep us
informed of your progress. I had a similar problem years ago. Hard to
remember exactly how I fixed it.

Dennis H.



The castellated track seems to supply a tacho signal. The off "main beam"
multipole magnets on rotating must be flux cut by the castellations inducing
a low level signal. May feed a drum loading/cut out as well/instead of
monitoring drum motor current - i don't know, not followed path.

Main problem seemed to be ps problem. Caps ok.
Decided to uprate .1A biasing Tr to .2A and pass Tr from 3A to 6A and
changing 13.6V setting zener to 15V to see what happened. Much better start
up torque, checking Vs I'd put a 13V Zener in by mistake
and drive volts was less at 11.5V down from 12V. Replaced with intended 15 V
and drive V then 13.6V but very little torque.
Returned to 13V zener and no problems since, caters with rinkled tape now
without cutting out, i doubt its a permanent cure
tho - weird.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/