My toughts on the Panasonic RQ-SX transport

Recently I have been (unsuccessfully) working on a a Panasonic RQ-SX60 and while trying to make it run properly I have developed some thoughts on this problematic transport



First of all, the ratio between the motor hub diameter and the right flywheel diameter is much smaller than other tape transports. Typically the motor hub is pretty small and the flywheel are a bit larger than those in the Panasonic and that results in a better torque on the capstan and a better decoupling between any motor vibration and the flywheel rotation.

Than the flywheel itself, beside being relatively small it also has a plastic gear underneath making the overall mass not big enough to have a decent inertia (i.e. basically being a good flywheel). By comparison the left flywheel has a bigger mass and indeed it pulls better the tape.

The poor right flywheel (small mass, driven by a motor hub not much smaller that the flywheel itself) has to drive a heck of a lot of other gears: there are two gears just to get to the clutch, the clutch assembly, then the gears on the left of the clutch (which would drive the cam gear) and finally the gears to connect the clutch to the hubs. Not counting the hubs and the flywheels there are also other 6 or 7 gears always rotating and driven exclusively by the right flywheel. It is no surprise that when the right flywheel is a pulling the tape, W&F is not exactly top notch (in my RQ-SX60 it actually plays horribly).

I cannot find any good point in this transport design: it is not too reliable, performs poorly and also a bit noisy. I'm not a mechanical engineer but i think they could have done a far better job than this one.

 

I would like to chime in and ask for help at the same time.
Recently I successfully replaced the belts of the SX10.
Upon inserting a tape is inserted, it spools up the tape in one direction for 1 or 2 seconds, directly followed by reverse direction - sprockets are turning and engaged, pinch rollers not.
However, when trying play, somehow the sprockets are not engaged but the pinch rollers are. The results is tape clutter in a few seconds.
I've opened it up, desoldered and checked for debris etc., but can't seem to find anything.
After soldering the connections and attempting to play, again the same faulty behavior.
It very likely is related to the design of the mechanism and the inherent quirks as described by @enryfox .
Any tips or tricks to help resolve? The player is in mint condition, would not like to see it go to waste.

 

Based on my experience with recent Sony mechanisms I would double check that any switches on the board that are supposed to link into the mechanism are correctly lined up and engaged together. Slightly related, this morning I was reading about an early Nakamichi cassette deck where if you didn't get the record switch properly engaged with the mechanism it would erase your tape when you tried to play it.

 

Thanks for the tip. Unfortunately I did not make any proper pictures. It is a pain in the rear end that you have to desolder all these connections to take it off, without the opportunity to do brief tests while the board and the mechanics are separated. I’ll remove the board once more tomorrow.

 

I have rebelted a different Panasonic, and on that it was only when I desoldered the board that I found I had the wrong belts
http://stereo2go.com/forums/threads/panasonic-rq-e27v-rebelting-and-big-thanks-to-mihokm.2154/
Looking at my photos I can see a switch on the back of the board that must sense some kind of position in the mechanism.
On a Denon HiFi cassette deck I repaired recently the problem was a dirty switch contact which again was supposed to indicate a position to the electronics but wasn't doing so.

 

I’ll check it as soon as I have time to open the unit completely (again). The mechanism is relatively similar to the SX53 that I took apart last week, no problems with that one though. I’ll look carefully for any type of switch.

 

You can manually engage all modes just by pushing the lever below the the solenoid and then hand turning the motor. Each push of the solenoid engage the program gear which makes 1/4 of a turn and change mode.
You can engage play mode and verify that all gears correctly turn. Verify if the clutch is still working, they all fail sooner or later.
Anyway, from this transport you will never get decent W&F, it will most likely sound wobbly. Even experts throw in the towel, at best you can make it run correctly, but it won’t sound satisfactory.

 

We miss tourists too, downtown is more deserted than usual while two years ago it was crammed with visitors from around the world. By the way right now you are missing hot weather with high humidity and afternoon thunderstorms ...

Going back to topic, recently one of the youtube channels I follow has documented a repair on an RQ-SX20: he has very good skills with repairing vintage electronics, but he's definitely not an expert on walkman's. He finds mostly the same problems as everyone trying to fix RQ-SX, and in the end you can hear what he defines satisfactory, but I think it is still too wobbly. An humble Rq-X11 plays way much better.

 

This may help

 

Thanks for sharing. Colin’s video actually triggered me and I opened this Panasonic up after watching it carefully.
I just desoldered the board again and shot a brief video of the 3 different modes that are controlled by a) the actuator and b) the direction of the motor.
I've only uploaded the 3rd and most important mode since that is the mode that the player can’t get into. The grey wire I use to test and trigger the actuator is connected to a 1.2V power source.
Notice how motor needs to be reversed very briefly to allow one light grey lever to unlatch. This lever is indicated by the artistically drawn green arrow (on my phone). The lever is sprung to allow it to pop back upwards as soon as it is unlatched. I removed a black protective plastic piece to see this lever in action, compared to the board in the photo of the first post of this thread. From then on both tape spools can be engaged alternatively by changing the direction of the motor, until the actuator triggers the first mode again.
I also noticed the rev-fw switch on the board that mates with plastic pins of the transport mechanism was not correctly placed back (it was me). See attached picture and screw driver pointing at the pins. I made sure to install the switch right but to no avail yet. The unit does not engage the tape spools in play mode but the capstan and pinch rollers do. My test tape is now pretty much dead.

Panasonic RQ-SX10 in play mode by Emiel posted Aug 2, 2021 at 10:30 PM

 

I honestly do not remember the motor had to change rotation direction to fully engage modes. In this type of transport, the motor always rotate in the same direction except when in FF/REW mode as it needs to move that sort of pendulum to connect one of the hubs. The only information the CPU has is the actual mode engaged (via the mode switch also shown in Colin's video) so i'm not sure it has any way to determine when to reverse rotation direction. Other type of trasnports (RQ-X) use motor direction to change mode, but they are completely different.
I think there might be something wrong in the lever not latching: from recollections of my experiments, after engaging the solenoid, by constantly rotating the motor in the same direction, play mode would engage and take-up hub would start rotating through the clutch assembly. Another push of the solenoid and reverse play is engaged, always with the motor rotating in the same direction.

 

After looking closer at the photo of post #1 and comparing it to the player in front of me, it seems that the coiled central spring is missing..
Pretty sure I did not get that one in one of my eyes, but it is missing nevertheless. I need to check the few Panasonic units I have still left for the same type of mechanism for a replacement part..

 

@Emiel That is the clutch and on this transport it almost always fail: black plastic retainer ring cracks an the clutch falls apart. In my picture i have replaced the plastic retainer with the brass replica by MMihok.

 

I’ll check FYA this week @enryfox as I still need to place an order for a few belts. Did not think of it before, but it seems easier than ripping apart another device!

 

Would you by any chance have the measurements of the spring that is underneath this retainer?

 

I'm sorry but I no longer have any Panasonic Walkman with such transport. I like all my units to be working and those walkman are unfixable, after ageing it is very hard to get decent W&F.
Regarding the spring, more than the size, what matters is the spring constant (i.e. its stiffness): too weak and torque is not enough, too strong and torque is excessive making the transport very unstable.

 

Thanks for the answer. I’ll order a few springs soon and will post the results here.