I just bought a pretty nice JVC PC-30, it's missing one volume knob and it has a little quirk. Regarding the missing knob - how do you solve such a problem? I have removed the remaining knob from the slider because it was hard to operate both volumes simultaneously. I'm thinking about looking for a pair of different fitting knobs. Regarding the quirk, the symptoms are - in reverse play, auto stop or auto reverse doesn't work, it just tries to spin the left spindle. Auto stop in rew doesn't work too. The left spindle seems to have less torque than the right spindle. The original owner told me, that all rubber parts are new - belts, pinch rollers, idler tires. What could be the problem? Does anyone have a service manual?
I noticed another thing, when I'm in reverse play and press stop, the reverse switches to forward play (meaning when I press play again it starts playing forward instead of continuing in reverse play). I think it is ralated to my auto stop problem ...
I think, I know what the problem is, the rev take up reel assembly. It consists of the take up reel and two toothed wheels, all of them are able to rotate independently and are coupled by some slipper clutch - sadly there seems to be no adjustment of it. Between the two toothed wheels seems to be some felt but I have no idea what kind of clutch is between the reel and the wheels. The lowest wheel has to stop to engage the auto reverse/stop mechanism I was thinking about interchanging the fwd and rev reel assemblies, to make sure the problem is in the reel assembly but they have different part numbers in the SM, I'm afraid they are not the same (not interchangeable).
I did some torque measurements: f. play take up 60, back tension 15 r. play take up 15, back tension 5 ff 80 rewind 20
These measurements seem to be off: takeup torque should be similar on both FWD and REV, and more likely closer to 30-40 g x cm. Back tension should be more or less similar, if I were to guess, I'd say probably closer to 5 g x cm. Rewind should be higher than 20, FF is likely good as it is. Check the supply reel, as that seem to have some slippage, indicated by both low REV torque and low rewind torque. More pictures with how the mechanism looks like will be of help.
I agree. The torques for forward and reverse should be similar The pictures I have taken are ugly. Here are two of the "better" ones: I can post the tape mechanism exploded view from the SM. Here are some YT videos: In them you can see a lot more how the tape mechanism looks and works, than from my ugly pictures.
This is the auto-stop mechanism ? It's interesting that the mech looks to be a more complex variant of the Tanashin-type mechanism. There are 2 front idlers that connect the capstant to the table reels, what purpose do those have ? Are they for FF/REW ? In this type of mechanism, the clutch is usually in that small black pulley driven by the flywheel. Is that the case here ? Are there any other clutches ? You mentioned something about a felt pad in the toothed wheels area. Can you describe that more specifically ?
Yes, it is the auto stop mechanism. The idlers are for play (right for f play, left for r. play). They are driven from the capstans, there is a toothed "ring" on them and they drive the upper toothed wheel of the reel assembly. FF and Rewind is driven by the belt from the forward play capstan to the black wheel in the center (RF CLUTCH ASS'Y in the SM) and then by toothed wheels to the lower toothed wheel of the reel assembly. There seems to be a felt between the upper and lower wheel of the reel assembly. It is visible on this ugly picture: To my knowledge there are at least 3 clutches, one in each reel assembly and one in the FF/Rewind gear in the center.
In the linked videos things are much better visible than in my crappy pictures (and in motion): in the first video 01:18-02:10 front of the tape mechanism 02:11-3:27 back of the tape mechanism in the second video 0:23-0:40 back of the tape mechanism, motor plate removed 4:30-6:00 idlers working 6:50-7:18 FF, then play in the third video 0:42-1:10 front of the tape mechanism, idlers working 03:40-3:53 clutches visible Part of the auto stop/auto reverse mechanism seems to be under the reverse take up reel, the rest is on the right top on the backside of the mechanism. Screenshot from the first video:
I have looked carefully at the videos provided, the only one that seems to point in some direction is the one in English. What has catched my attention are those 2 rubber idlers. The low reverse torque can be caused by either a slipping rubber idler or a problem with the table reel clutch itself. The low torque can be related to the auto-stop not engaging, if the outer part of the clutch is not rotating at all, but slipping at the rubber instead of the clutch. It seems indeed there are 3 clutches in this unit: one is on the belt driven pulley as in all Tanashin-type mechs, and another 2: one on each of the table reels. Did you replace the rubber on that 2 idlers ? Marian might have the correct dimension in stock, check his website. I suppose the belt driving that cam gear is not slipping, as that could also be an issue. The auto-stop mechanism itself seems similar to the one used in Sony mechanisms, with a rotating cam and a lever that gets pulled in a certain position when the drive table reel stops rotating, at which point the cam will engage the stop.
The previous owner told me, that all rubber parts were replaces - both pinch rollers, both idler tires and all three belts. From the look of the rubber parts, he told the truth. From my observations the problem is in the left spindle assembly (the one with the auto stop mechanism behind it). The idlers are not slipping. When I stop the spindle with my fingers in reverse play, the upper toothed wheel in contact with the idler keeps spinning. When I stop the spindle with my fingers in rewind, the lower toothed wheel in contact with the "center" toothed wheel keeps spinning. The auto stop mechanism is controlled by the movement of the left spindle assembly only. When in f. play or ff, the right spindle is driven "directly" and the left is driven only by the tape movement. When the tape movements stops, the whole left spindle assembly stops too and the auto stop mechanism engages. When in r. play or rewind, the left spindle is driven "directly" and when the tape reaches the end, the spindle stops but just the spindle. The toothed wheel(s) which is driven (lower in rewind, upper and lower in play) keeps spinning and the auto stop does not engage. I have to stop the lower toothed wheel with my finger for the auto stop to engage. My conclusion: - the lower toothed wheel of the left spindle assembly controls the auto stop - the clutch between the toothed wheels and the spindle is worn out and has not enough torque - the clutch (felt) between the two toothed wheels seems to be fine, because in r. play the upper toothed wheel is driven but the lower keeps spinning even, when the spindle stops I have no idea, how the clutch between the two toothed wheels is made and if it is fixable. I have to admit I'm afraid to disassemble the spindle assembly because if I break something, I'm out of luck. I'm considering I'll use it as a non reverse tape and I have to keep an eye on it when rewinding and remember to stop it by hand ...
I agree with your conclusion, it's likely the clutch in the reverse/REW table reel that does not have enough grip. That would also explain the low takeup torque on reverse play and on rewind. Don't think much can go wrong if you remove the table reel itself to see how it's constructed. The clutch has to maintain some pressure on the felt pad to work, likely by a spring. If the spring is a normal coiled one, it is a possibility that the retaining washer has cracked and the spring does not sit in its fully compressed postion anymore. Depending on how this clutch is built it might be easily repairable or it might need a custom manufactured part.
I'll try to remove the reel assembly. There seems to be a spring between the reel and the wheels - there is a gap, where you can see a part of it. And it seems, that part of the auto stop mechanism is under the reel assembly. I'm afraid the reel assembly is pressure fit together and I really, really don't want to break it.
Try removing this split washer (it looks like one, although the picture is grainy) and see if the table reel slides out. It shouldn't require force to pull it out after the removal of that split washer. Pay attention as there might be a second anti-friction washer underneath it and most likely another one on the back side of the reel.
I finally found some time (and determination) to continue to work on the JVC. After removing the split washer, I could easily remove all three parts of the assembly. Here are some pictures: On the first image you can see the clutch between the two wheels (felt on one part and round grooves on the other) On the second image you can see part of the the auto stop mechanism (wheel with two prongs) and the second wheel from the side where the spring presses against it (the small lighter ring). The whole "clutch" between the reel and the wheels is done by the spring in the reel pressing against the wheel. Detailed pictures: (the small lighter ring - the ring is just grease, after cleaning, there is just barely visible ring, see on the last picture) And there is not enough torque transferred. The question is how to fix it? Try to stretch the spring somewhat? Clean the grease? (it seems it is original, there is some on the other reel in this location too) Try to make the part of the spring which presses against the wheel rough with some fine sandpaper? Try to make the part of the wheel where the spring presses against it rough with some fine sandpaper? Any other ideas?
It's an interesting design... Given how the 2 clutches are designed, one thing is for sure: I would not expect the torque to be the same on both sides. The one with felt pad and circular grooves is going to have more friction in it than the one with just a spring. The only way that I see to compensate for this is to either: - stretch the spring a bit and eventually use a thicker grease; some grease should be used as metal on plastic will inevitably create wear; - replace the spring with another one that has larger wire diamter, so it is harder; The ideas with making the surfaces rougher will probably work, but will also create wear if not greased. Does that auto-stop wheel (with 2 prongs) have any friction material on the other side ? Or signs of something that has been removed/is worn out ? To me it seems like something is missing, as just that spring is not enough to create the necessary friction.
There is also a clutch hidden behind the two pronged auto stop wheel. The second reel without auto stop is almost the same, it's just missing the auto stop part, there is a small spring instead (and it works fine). I assume it's in original state, it doesn't seem that someone removed the split washers before me. Another idea - put some (metal) washer between the wheel and the spring? Or grease it just a tiny little bit? (there is much less grease on the second reel assembly)
It makes more sense now. First, I would double check those felt pads and try to clean them. It is possible that the glue that holds them oozed into the material, reducing the friction. The idea with metal washer is a very good one as well. You can even put more than one, glueing them together. Given there is a clutch on the second one as well, how much you grease the spring is probably not going to make much of a differnce. I would look for different springs (assuming the felt pads are in perfect condition), you can find them on Aliexpress at very low prices. You need to search by outer diamter, length and wire diameter. You can either choose a longer spring with same wire diameter or larger wire diameter with same length. The bad part is you will have to wait for these springs to arrive.
I was inspecting the felt closely and it seems fine to me. And the friction between the wheels is similar on both reels. So I think that part is fine. The problem is the friction between the middle wheel and the reel, that differs between both reels significantly. I'll try to experiment with washers first, maybe stretch the spring a little bit and then look for some other springs ...
After another inspection and some quick experiments it seems, that the problem is on the other end of the spring (the one in the reel). The spring rotates in the reel really freely with minimal friction - that can't be right ...
