Silver ST-868 Partial Refurb

[429CV23]

I finally got around to doing some work on the ST-868. The meters were still pretty problematic, and the supply hub would spin ahead then stop to catch up since I had not replaced the belts and it was lacking back tension. I recapped the meter board and most of the play/rec amp board. The meters now work very well.
I replaced the belts which fixed the supply reel issue, and I was surprised the speed was close, and the W/F was pretty good for a boomer: 3110Hz using a 3150Hz HPR cal tape, and W/F was 0.06-0.07%RMS.

How is the speed adjusted on the 868? I have the 858 SM but have never seen the 868 SM. The 858 SM shows speed adjustment is internal on the capstan motor; the access hole is not present nor accessible on the 868. I'm assuming there is an adjustment pot on the play/rec amp board but don't want to start slinging adjustments on the wrong pot.

Has anyone replaced the 36pin rec/play switch? Can the switch be sourced anywhere? I'd much rather replace it than disassemble and clean it. Cleaning it without disassembly is likely not going to work too well due to its overall length.

Thanks!!

 

[BoomboxLover48]

How is the speed adjusted on the 868? I have the 858 SM but have never seen the 868 SM. The 858 SM shows speed adjustment is internal on the capstan motor; the access hole is not present nor accessible on the 868. I'm assuming there is an adjustment pot on the play/rec amp board but don't want to start slinging adjustments on the wrong pot.

Check the condition of the pinch roller.
In some cases, a glazed pinch roller can cause speed variation. Take up hub will pull tape more when the pinch roller rubber has hardened and shiny. The pinch roller rubber has to press the tape to the capstan and regulate it's supply speed moving over the cassette head.

 

[429CV23]

The pinch roller is suspect due to age, but is working OK for now. W/F at 0.07% is pretty solid for a boombox; at that level would not be audible. Most of my Nakamichi decks have only slightly better W/F (0.02-0.05%). I did not measure W/F with the old belts for comparison (wish I had).
I'd like to adjust the speed as it's running a bit slow; 3110Hz on a 3150Hz cal tape.