I recently had two WM-D6 units that showed similar symptoms. Both units had CP601 repaired per @Deb64's prescription. They both looked to be successful repair job in the beginning, and as I was running them for hours, they started showing up bad wow flutter. I thought initially they just need RV601 speed adjustment. After experimenting, I found: Unlike normally functioning unit, these units show speed fluctuating greatly with sine curve at lower speed level of RV601 Speed fluctuation reduces and almost not visible at exactly on-spot speed (3008 Hz per my test tape + WFGUI) After running for about 20 minutes (or shorter as symptom develops) the speed starts to drop randomly, eventually creating stuttering symptom. This creates scratching sound from the motor When this happens, we can detect that there's signal noise detected at pin 3 of CP601. This was strange to me since pin 3 is an input from FG901 (Frequency Generator) and they don't create noise when the wire was separated from the board (though as a result it would run fast). This symptom is recorded as a video here. Since pin 3 would not show that drastic disturbances coming from the op amp of CP601 if capacitors didn't fail, my suspicion was at these two capacitors C1 and C2. C1: 47 nF C2: 22 nF My repair was very simple. I didn't have SMD capacitor kit readily at hand, but I had ceramic capacitor kit. I took them off from the board, put wires on where they came off on the board. I used those wires to solder capacitors on. They were placed at the back of the board and wrapped with electric tape. I am testing the repaired CP601 now and it's already improved when tested at lower range of RV601 (no fluctuations). W&F is now measured at 0.047% (before this repair, the best number I was able to obtain from this unit was 0.07%) I will test for another week before come back with confirmation but it looks pretty good so far. --- UPDATE 10/22/24 The unit is still measuring at 0.047% W&F 10 sec max. It ranges 0.03 ~ 0.05% when eyeballing. Considering the 3khz test tape sourced from eBay (was recorded by K555ESJ deck) itself is not perfect, it could really be sitting in the spec 0.04%. --- UPDATE 10/29/24 I ended up replacing capstan ring and that made the W&F worse to 0.065%. It runs quieter mechanically, but probably it needs some burn in time. Also SMD caps arrived and were installed. In the process I corrected the C2 value to 22 nF. 10 nF cap created the same issue as that initiated this whole repair process. (I measured 10 nF from the one I took off but I only had 22 nF at the time and used it instead and I find that was simply a pure luck!)
