• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Initial repair guidance for dual well Kenwood cassette

R

Rocky_714

New Member
Hello all,

I have a Kenwood CT-2050 dual well cassette deck that I need some initial guidance on trying to repair. The deck was within a system that sat for a very long time because of an amp that was in a repair shop for a year and a half (and ultimately wasn't repair when I got fed up) and then for another untold months while I decided what to do about replacing it. The disuse led to the current curiosity. I'm thinking that it is something electronic because the symptoms are identical for both wells but it concerns the transports. The belts appear to be intact for both sides but neither well will enter PLAY mode in either direction (the machine is bidirectional). Each transport will fast wind in both directions to the end of the cassette entirely. When one presses PLAY, the heads-guides-pinch roller assembly will rise fully up to the tape for 2-3 seconds but auto-stop and retract. The capstans seem to be physically connected to the tape reel drives so I think that it is driven when PLAY is engaged (but I'm not sure since I can't see the detail of the gear connections between the plates of the drive system) but the tape reels don't move so I don't think the pinch rollers and capstan meet so there is no tape movement. No tape jamming occurs. Since the behavior of both wells is the same, I'm guessing that something in the logic is telling the system that the drives have stopped and that auto-stop should be triggered, or that there's no tape in the well and that the drive should be stopped.

I have the service manual but it doesn't tell one how to do anything (like troubleshoot), only the exploded view of the mechanism and the schematic diagram. Also, I'm not an experienced debugger/tech but a rank amateur. I know how to solder and have basic knowledge of how to read a schematic but my practical knowledge is severely limited. So, please, be very specific and dumb things down and I promise, I won't be insulted. If you're looking at the schematic of the service manual as I am, give me grid coordinates if you know them. If not, be as remedial as you can about what the specific control or area of a circuit I should look for. If it is mechanical, let me know what you're thinking I should look for. I very much appreciate all suggestions. Thank you greatly.

-Rocky_714
 
Register to hide this ad
Hi all,

Did I do something wrong here or did I just baffle everyone? I'm not immune from criticism so just let me know. On the assumption that this just a TLDR problem, let me summarize:

Unit: Bi-di dual well cassette Kenwood CT-2050

Symptoms:
1) Both wells behave the same way: wells won't enter "PLAY" mode. Head assembly with pinch rollers rise momentarily but receded after 2-3 seconds no matter which direction play is desired
2) Belts are intact
3) Motors will wind tapes in both directions in both wells so reels operate under fast wind conditions

Surmise:
Suspect that something electronic is going wrong, possibly sensors, since both wells behave identically. If there were mechanical failure, it would have been too unusual a coincidence for both wells to be affected identically.

Question:
Where should I start to look/identify in the system or test to identify where the problem lies? Professional repair is likely to cost more than the deck is worth.

Thanks.

-Rocky_714
 
The first thing I'd check, and I don't know the correct name for it, is the "run detector". It's usually a pulley, driven by a small belt, carrying a circular magnet. There will be a sensor or reed switch next to it. Make sure that magnet is actually turning, or the unit will shut off after 2-4 seconds. A bearing could be gummed up, preventing the magnet from turning.
 
Hey,

Thanks for responding. I'll go looking for that. The machinery is pretty dense in there but I'll check. Here's another piece of information I just gleaned while poking around that might suggest the direction is elsewhere:

Pressing the REC/ARM button, which is their version of a REC/PAUSE button which prepares for going into recording but doesn't require tape motion, does the same thing as "PLAY". That is, the head assembly rises for 2-3 seconds and then retracts and undoes the button press. Since it doesn't require tape motion, I don't think a tape motion detector would inhibit REC/ARM.

I tested the tape selector (Cr02/Norm) and Record inhibit (tape punchouts) sensors, at least on the one side and they're working. I'm not sure the head assembly would rise if those weren't working but it was worth a try.

-Rocky_714
 
In short, yes. The unit has one motor for each well. It runs and spins the mechanism for fast winding in each direction. Not only that, it spins at least part of the mechanism for the entire time while I try to engage PLAY until it shuts itself off and the head assembly retracts. I can't tell why there's no motion in the transport while the motor spins but there is motion of the motor and some belts while there's no motion of tape and reels.

-Rocky_714
 
OK, let's try this. Is someone willing to help with a little hand-holding here? I could use a little help in interpretation of the schematic. First, I believe the Kenwood KXF-W6010 is equivalent to my CT-2050 - it's just US vs Europe designations (the service manual covers four similar models). On the schematic of the service manual (easily obtained on hifiengine.com) on page 8, there is an element I'd like to check at the coordinate L8 in the schematic. It shows the head and controls assembly mechanism for the right well for the KXF-W6010. In it, it highlights a "Photo Reflector". In the exploded view, there is something called the "Photo Interrupter" (number 485 on page 12 of the exploded view) which I think are closely related. It feeds a sensor in the well of the cassette which is covered by the cassette carrier/cover when closed and uncovered when the carrier/cover is open.

I expect that it should have different DC voltages depending on the state of the door. I need to know what it should be when I measure what it is. Thanks for any help.

-Rocky_714
 
No matter, it appears that the "Photo Reflector" circuit changes state properly depending on whether the door is open or closed (reading changes by about 1V) so it's not this that's preventing the deck from going into play.

Anyway, if there's anything I can do to get more help here, I'd appreciate it.

-Rocky_714
 
I suspect the problem is still related to the issue in post #3. Somewhere in the deck is the run detector. Sometimes it’s on the tape counter run by a separate belt. Could be a light source is out or the counter belt is bad or a disc with black and white segments is somehow not spinning. You need to find what the deck is looking for to verify it’s working, and correct that.
I suspect if someone knew what that was they would let you know…
 
...Somewhere in the deck is the run detector...
Click to expand...

You're probably right. I guess I was interpreting it a little more broadly in the sense of "Look for the things that can inhibit running or PLAY." of which I thought the door closed sensor would be one. The door closed is one of many inputs to what I believe is the main logic chip. Unfortunately, there's no telling what the logic is or which of the inputs is important to PLAY.

So, yes, run detection would be important. But reels move in fast wind but not in PLAY. Capstans turn but don't cause tape to advance in PLAY. Tape counting moves in fast wind but not in PLAY. Where the detection for these not happening is not yet clear to me.

I'll still be investigating. Thanks for responding.

-Rocky_714
 
A common issue for mechanisms of this era is the grease. Whether be it tape, CD transport or turntable, anything that moves got grease, that has now hardened or absorbed enough moisture to impede movement. I don't know this mechanism, but if it's got sliding parts you may need to check and make sure that's that are not being prevented from fully engaging.
 
Thanks, loudnoises. I had to move on to other higher priority concerns for awhile but now I'm back and looking more closely at the issue. In the meantime, I found another CT-2050 for sale at an estate sale for cheap in which one cassette well didn't work (in the same failure mode as my original one) and the other worked fine. I thought I could use it as a testing set without risking much in the original machine. Although I knew I wouldn't be able to work on it for awhile while I addressed my other issues, I thought I had a good path going forward.

As it turns out, while I was away, the second well on the second machine failed as well. I didn't feel bad because it was cheap ($24). Nonetheless, I bought a set of belts for all four wells and changed only the originally non-working well on the second machine to rule out belts as a cause. Testing began, and I think, loudnoises, that you are closer to the cause than you know. My diagnosis, so far, is that the pinch roller is not pinching the tape or turning sufficiently in either direction to drive the tape. I tried to manually supply added pressure to the pinch roller in the direction of the capstan to see if the spring that normally does that had just weakened with age. Unfortunately, that didn't cause the pinch roller to start spinning. I could only conclude that there is too much drag on the shaft underneath the roller preventing it from spinning. Or is it that the pinch rollers have dried out too much to grip the capstan/tape to drive the tape forward?

I tried dripping some isopropyl into the pivot and working it in back and forth underneath the pinch roller to clean out any old debris or dried out grease that had accumulated underneath it. That wasn't enough to free it up to allow it to pinch tape. These experiments were done without tape present so if I can't get it to spin without tape, I can't believe it will spin with tape present. Anyway, loudnoises, I expect grease would be the next attempt but what kind of grease to use? I imagine it has to be thin enough to be able to work in underneath the roller but thick enough not to drip and act as a cushion over the pivot shaft. I have some "Optical and Instrument Helicoid Grease" that is used for camera lenses that contains Lithium and PTFE. Would that work? If not that, can you suggest a type?

Anyway, I worry that the shaft itself has cracked and can't be compensated with grease. From the service manual, it looks like the entire pivot assembly is the replaceable part, not the pinch roller, or the shaft, can be replaced independently. Looking it up at the Kenwood parts supplier does not even find that part so I may be out of luck on that. Let me know your thoughts on alternatives if you think grease might not work. Thanks.

-Rocky_714
 
I've only had to fix a few transports, you're already ahead of me! Lithium grease is usually good for plastics. I've also used some leftover food safe grease from a kitchenaid mixer repack. The only fully success I've had was a tascam 112, those were built to be fixed so I'm a little jaded.

Springs do weaken over time, and rollers are definitely a failure point. Terry's rubber rollers is the source for those, he'll fix ya up. I don't know if it's a grip thing but I always remember those rollers being soft and now they're all harder. Time or bad memory who knows? Tape mechanisms aren't as homogenous as the like 4 different cd transport mfgs, everyone built their own.
 
So, further study has revealed additional detail which seems to be true of the pinch rollers of both decks and both of the rollers in each of the wells (one for each direction of tape travel). The pinch rollers have a two part construction. The rubber itself appears to be mounted on a plastic sleeve on which the two are meant to spin together against a plastic shaft that is on the assembly that pivots toward and away from the capstan depending which of the auto reverse directions are selected to play. However, due to age and the drying out of the rubber, the roller has detached from that sleeve and now spins independently of the sleeve. Certainly not ideal but in the final analysis, I don't really care whether it spins with or without the sleeve as long as it pinches the tape to drive it forward.

Now, from the service manual, it is not at all clear how to get the pinch roller assemblies off (or back on) the decks, the right roller shown here:

Right_pinch_roller_assy.jpg
There's no head or circlip or anything like that on the pivot mounting point of that pinch roller assembly. It looks like a press fit of some sort so it's likely easily broken when removed even after the tape drive assembly is removed from the deck, no mean feat by itself. So, although Terry's Rubber Rollers (great reference, BTW) would probably be the ideal solution, I'm leaving it as a last ditch solution. The second (estate sale) deck might have to be the sacrificial lamb since I'm so likely to break so much trying to remove the pinch roller assemblies to send to Terry's before learning how to do it properly, not to forget how it will get re-attached when it gets returned from them.

Amusingly, the service manual has no replaceable part numbers for the 8XX parts in the diagram. It does for the 426 and the symmetric pinch roller assembly on the other side. I went to the Kenwood parts supplier's web site and looked them up and they came up empty. I'll probably email them to ask about them but they're probably just discontinued and unavailable. I'll follow up but it's probably just a dead end.

My first attempt is going to have to be an in-situ repair attempt which I'm in the midst of right now. I'm using Rubber Renue to rejuvenate the pinch roller itself and increase its grip characteristics. The first application was promising if not entirely successful but a few more might work. I'm also going to try that optical grease I mentioned even if it is between roller and the sleeve. With the rubber hardened, the interior cylindrical surface will have a more plastic-like behavior giving a plastic-plastic sliding character between the two. Between the two approaches, I think I can get a workable solution. I don't think the Rubber Renue works for the long term but repeated application can be done without removing from the equipment rack. Finally, disassembly and Terry's is the backup with the second deck as the training ground. Call it a learning experience if not cost effective. Thanks to loudnoises, Bradbrews, and ConradH for their helpful guidance in responding to my inquiries. More guidance is welcome and I'll report back as new insight is gathered.

-Rocky_714
 
Usually pinch rollers are press fit to the bracket, often on only one side.
To replace them you usually need to remove the whole bracket at its pivot point. Then use a suitable tool as a punch to drive the pin out. Put it over a piece of wood with a hole for the shaft to prevent bending the bracket.
New rollers are available, just measure ID, OD, and width.
 
Bradbrews said:
Usually pinch rollers are press fit to the bracket, often on only one side.
To replace them you usually need to remove the whole bracket at its pivot point. Then use a suitable tool as a punch to drive the pin out. Put it over a piece of wood with a hole for the shaft to prevent bending the bracket.
New rollers are available, just measure ID, OD, and width.
Click to expand...
Thanks, Bradbrews. That's important to know. I'm assuming the bracket will pop out from the pivot point with an appropriate pry tool without too much force and will do so non-destructively. And will it press fit back on without a new pivot post, you think? Also, do you have a good source for the pinch rollers?

It appears that I'm heading in that direction. The Rubber Renue/spin lube solution seems to last less than 24 hours, not the 24 months I had hoped.

Thanks again for the help.

-Rocky_714
 
Just to be clear, I was talking about the roller pivot,not the bracket. The bracket moves, so it must be free on the shaft it turns about. There must be something that keeps it in place.
 
I understand you were mostly talking about replacing the roller in the bracket. However, you did mention that that

...you usually need to remove the whole bracket at its pivot point...
Click to expand...

which also looks like it's a press fit from what I can see. I was just asking if you thought that that would be a non-destructive pry tool removal and restoration without new parts. The service manual is not at all clear on that and once removed, it could be a point of no return.
 
You must log in or register to reply here.
Back
Top Bottom