AKAI VS-5 very slow and unstable capstan speed

[dj_fivos_sak]

Hello guys. So I digged out this 37-year-old VCR yesterday to take a look at it since it wasn't used for a long time. I repaired a broken loading gear and now the machine threads/unthreads fine. But, there seems to be a strange issue on playback. The capstan motor seems to run very slow and there's not much difference if I try to adjust the servo of the motor, as per service manual. I double-checked the capstan belt and the pinch roller and they are both in great shape. Even if I release the back-tension lever, the problem remains the same. To help you understand the issue, I captured a couple of videos from the machine playing, one of which is a 440Hz test tone that I recorded with another good machine. Link for the video files:
https://ufile.io/qbwb2
Any help would be highly appreciated.

Fivos

[vhs doctor]

Hi

During playback if you select FORWARD/REVIEW function the capstan motor increase speed or not?

If you are sure that the capstan motor run slow. Follow the circuit of the capstan motor and check the capstan drive circuit probably it is IC. Replace the electrolytic capacitors in this circuit and also replace the capacitors in PSU. If nothing change then replace the capstan driver IC.

I hope that you can adjust again the back tension and the servo circuit in factory settings.

[dj_fivos_sak]

Thanks for your answer. Yes, the forward and reverse search functions work fine. I didn't adjust the back-tension screw. I just pulled the arm away from the tape while it was playing. The capstan motor board is behind the mechanism and it's hard to reach it. I will recap the chroma board as well, because the color also seems to be unstable. It uses Panasonic ICs everywhere, like the NV-7500 (except for the syscon board, which has big AKAI ICs).
EDIT: Added some pictures of the bottom PCBs.

[Freya]

If you look at the pcb in picture 3 you can see there is possible evidence of leakage causing darker rings on the board around the capacitors.

[dj_fivos_sak]

I think that's just circuit glue. I will replace them anyway...

[vhs doctor]

If in FORWARD/REWIND the capstan motor increase speed the motor must be OK. Follow the wiring of the capsacitortan motor, find the driver IC and check all the components in his circuit. Check also the voltages under load and the capacitors on PSU.

Also in my personal opinion never start total recap or recap other PCB board that it is not related to the problem. I follow a rule (personal opinion) that first repair the VCR then check that all functions work properly and then restore it.
Also when you recap do the procedure section-section ex replace all the capacitors in chrominance and luminance board check if this section work fine and then continue.
It is very easy especially on first machines with a lot of electrolytic capacitors to make mistakes in capacity polarity etc and in the end you maybe have a lot of electronic problems and really difficult solutions and repairs

[Welsh Anorak]

Hi
Agreed - I would recommend replacing only what needs to be replaced or ones that are known to give trouble - and test after every replacement. However I think you know this!
I would worry about that NiCad in the middle of the board - that can leak nasty corrosive chemicals.
If the capstan's running then I think the FG pulses will be there, otherwise it would shut down. So the problem must lie somewhere in the PB servo loop. A 'scope is useful here - monitor the pulses and see where they go. My money would be on a capacitor in the loop.

[dj_fivos_sak]

Thank you both. I won't have access to the machine until July. I will remove the Nicad battery. It isn't leaking but I guess it will. I also don't have a scope so I will start by recapping the whole servo board.

Fivos