View Single Post
Old 5th Jun 2022, 3:15 pm   #1
Krolroger
Pentode
 
Join Date: Nov 2017
Location: London, UK.
Posts: 108
Default Beocord 5000 (Type 4715) Capstan Motor Speed

Hello All,

I posted here previously about the motor run cap in this player. I put it back into use with the original cap but was still having some capstan motor speed issues so I've pulled it apart again to have a look at the motor servo board. (In fact I have now put in a couple of back to back elkos which seem to be fine).

The problem is that in Play mode I can't adjust the capstan speed to bring it to pitch. In Stop mode, I can tweak poti R13 to achieve the specified 500Hz signal from the capstan flywheel inductor but in Play mode the signal falls to around 475Hz and no amount of adjustment will bring it back up. This means it plays about a semitone flat / 5% slow.

When I invoke Stop, the signal will rise again to 500Hz or more depending on where R13 was set.

Rail voltages are correct (-11 and +12) and in Stop mode specified voltages and waveforms seem to be pretty much on the money. All caps have been replaced, diodes and resistors checked. In addition, I have changed power transistor TR2 which acts as a resistor in series with the motor and the bridge rectifier D3.

Would I be right in thinking that the 8 pin op-amp (MC1458CP) is now the prime suspect as the feedback loop appears not to be working? Easy enough to replace, but I would greatly appreciate any input.

Thanks again!
Attached Files
File Type: pdf 4715 Motor Servo Board.pdf (3.31 MB, 48 views)

Last edited by Krolroger; 5th Jun 2022 at 3:36 pm.
Krolroger is offline