JVC CX-F7K restoration

Valentin · Dec 26, 2022

This is one of my favourite walkmans out there. There is something that I like about full logic units with a separate motor for the logic control, like the WM-7 or this JVC. It's mostly related to the experience created when pressing a button and hearing the mechanism engaging. And I also like the simplicity of the mechanisms used in units like this one,
I think this JVC is almost as simple as a mech can get.
It's also the only one I have seen where motor turns in both directions depedning if it runs in forward or reverse. This simplifies the mechanical side a lot.

Of course, the unit as an assembly is far from being simple: there are a lot of electronics packed inside a very small case, making the disassembly process not as simple as in others.

NOTE: this thread is intended mostly for entertainment purposes and it's not intended to be a repair tutorial.
I would rate this repair a 8/10 as a difficulty rating and consider it's one of the most difficult compact cassette walkmans to repair, especially due to the fragile flex PCB and the requirement to repair the clutch (which although straight-forward is not what I would consider a DIY job).
Just replacing the belt requires to disassemble the entire unit and mechanism, so beware of sellers on ebay pretending to have refurbished a unit like this.
Not to mention replacing the belt alone in this device won't fix its problems, as the motor will also need lubrication and the clutch will need to be repaired.
The problems that I state below are to be found on all CX-7/CX-F7, CX-5/CX-F5, CX-R7 and CX-V9 of this vintage, so keep this in mind if you intend to buy such a walkman.

Despite many of these walkmans still work, they will need to be serviced because:
- the belt has strectehed and will slip during FF/REW;
- the motor will start squeeling due to lack of lubrication;
- the broken clutch will cause low takeup torque or even no torque resulting in eated tapes;
- the CX-(F)5 and CX-(F)7 will also need new capacitors;

DESIGN:
In terms of constuction it uses a big flex PCB that is used for both the main PCB and the cassette lid PCB. The part of the flex where the components are mounted is glued on a thin aluminium sheet.
It uses a single AA battery and a typical DC-DC converter with a transformer (a topology found in many walkmans, portable recorders and even Discmans). All the mechanism functions are controlled by a microcontroller that reads the position of the mechanism using a sliding leaf switch.
There is a second mode switch on the governor board (seen in first picture), that controls the motor's direction. Given the simplicity of the mech, the table reels are engaged only by the torque of the clutch, so the need to reverse the rotation of the motor.
The auto-reverse function is electronically-controlled by reading pulses from an IR sensor.
Something else worth mentioning is how the radio function is implemented: given there is not enough room for a variable capacitor in the cassette lid (where the tuning pot is located), the tuning is done with varicap diodes.

REPAIR:
Repairing the mechanical side consists of lubricating the mechanism (capstan bearings, table reels and motor), repairing the clutch and reinstalling a new belt.
On the electronics side, there are 5 electrolytic SMD capacitors that are leaky and need replacement. Besides that, cleaning the mode switches and potentiometers is about all that needs to be done.

Tutorial for clutch repair: https://stereo2go.com/forums/threads/jvc-cx-5-cx-7-cx-f5-cx-f7-cx-r7-cx-v9-clutch-repair.8461/