SONY TC-K555ESA: Servicing the Mechanical Block
In the past somebody attempted to replace the supply pinch roller on this machine and failed to do so. Furthermore he even managed to destroy the tape path alignment. Fortunately the heads screws were not touched. It is a well known problem of the TCM-200D class mechanics that a worn out supply side pinch roller would cause tape skewing. So let's change these rollers. Or better let's change every rubber part in this deck. There is the cam belt and the capstan belt. While the latter is easy to replace, the former requires a little bit of outside of the box thinking.
This is the mechanical block on my tiny workbench.
View from above.
And a close picture with the tape path. Pretty unique and weird erase head with transparent sidewall so that you can see the coil windings.
Disassembly is now in progress. Notice the worn capstan belt. I turned it on the other side a couple of years ago for a bit more grip.
While here I decided to replace the electrolytic capacitors on the two small PCBs affixed to the mechanical block. I started with the quartz frequency reference circuit. Only a couple of parts here to change. I used Nichicon PWM series replacements.
All electrolytic capacitors are replaced.
...PICTURE FOLLOWS SOON...
The take-up side pinch roller is very easy to replace. It pops out easily if you put back-force between the roller and the roller arm. Use a soft plastic tool for this operation. The supply side pinch roller however is a little bit difficult to get out. Removal of the pinch roller arm assembly is pretty easy. Warning: doing so breaks the tape path alignment. But this is the expected result.
Then getting the roller out of its axle requires an improvised rig. I used a bicycle brake cable stopper as spacer, the take-up pinch roller axle as pushing rod, and a vise to apply even and controlled pressure on the pushing rod. If you align everything perfectly in line, the operation is done smoothly. Be very careful though, don't push the rod all the way in, or the supply side axle will get out of the roller assembly. And it is hard to push it back in place. I applied even pressure in a very controlled manner and observed when the axle cleared completely the pinch roller. Thus, the roller gets out easily and the axle stays engaged in the left guidance hole, ready to be pushed back through the hub of the new pinch roller. This is all possible because the pushing rod (i.e. the take-up side pinch roller axle) is a tiny bit smaller in diameter and can be easily retracted by hand from the fixture hole of the pinch roller arm assembly.
In the picture below, the old roller has already been removed and I'm preparing to install the new one. You can also see the pushing rod.
I put a drop of oil inside the pinch roller hub and pushed the axle in reverse order using the same rig.
New roller is installed. Old roller is out.
Then I mounted the pinch roller arm assembly back in its place on the mechanical block. Here are both rollers happily replaced.
Now regarding the belts. I have removed the capstan flywheels, the take-up side also being the induction motor. Care needs to be taken since there are some washers on both sides of the capstan axles, relative to their respective bearing.
Then I removed the front plastic decorative plate to gain access to four screws that separate the capstan bearings carrier from the main mechanical block steel plate. I also loosened the circuit board on the back side of the steel plate and I was thus able to access the cam belt. I used a fine tool to get it out of there and then I inserted the new belt.
Surprise, surprise. Somebody was here before. And he didn't find a suitable replacement belt thus he tied a knot in a similar belt and transformed its dimension into something that worked. Ugly as hell. Here are the old belts versus the new ones.
I mounted everything back in place in reverse order.
I then oiled the capstan bearings with Isoflex PDP 65 oil which I had left from servicing Revox and Studer machines. Then inserted the capstans with care not to scratch them. The washer are also in place. I added the capstan belt and secured everything back in place with the steel plate which is also home to the quartz frequency reference circuit.
I cleaned everything with IPA and the mechanical block is ready to go back in the deck.
Now it is ready for alignment. I did the initial alignment with mirror cassette. Then I used a test cassette with various signals and a dual analog millivoltmeter connected on the outputs of the deck. I thought the alignment would've been harder but in fact it was quite easy to do it.
At the end I secured the alignment nut with some nail polish.
And a picture with the flash activated so that you can see the new pinch rollers in their final position.
So far so good. The mechanical block is very stable. I have tested ferric, chrome, and metal tapes. All run smooth without tape skewing. Now let's record some music!