Japanese 'green' thread lock

[ktm-don]

I just picked up a HK 670 in reasonable shape. The tuner section has a small gear on the end of the strung pulley that drives a larger gear on the tuning capacitor.

In the process of pick up and handling, the pulley backed out of position, allowing the small drive gear to fall off. It seems to be oriented by a double D cutout and the flattened shaft of the pulley.

It was a bugger to get back into place without taking down the entire dial string, something I'd like to avoid. When I did get the gear back in place, I did not index the gear teeth perfectly, as the dial indication is off from the actual station frequency. There seem to be two ways to re-align the dial, rotating the pulley on it's shaft or moving the pointer on the string.

So, back to the original title, the pulley is secured by two screws clamping it to the shaft. They are locked in place with a familiar green compound that I've seen on other vintage units. I tried chipping free as much as I could, but I was unable to budge the screws. They are small, and I did not want to destroy the slotted heads.

Anyone have a trick for releasing this stuff? Heat and solvents come to mind, but I can't really apply heat to the pulley bushing, as the pulley itself is plastic, and 40 years old. Moving the pointer looks challenging as well, bits of glue secure the pointer to the dial string.

Any suggestions would be appreciated.

 

[Tom B]

Those tuning caps have the same issues whether HK or others. The large pully and its shaft can easily pull off. When this happens, the "spring Load" on the set of gears connected to the tuning cap disengages.
To repair it,
1) I remove the grey pot metal bracket for the tuning cap (2 small flat head phillips #1.
2) no need to remove the large pulley from the shaft, but doing so makes it a little easier
3) you should have the shaft, small grey gear, small special washer (the washer locks the tuning cap from overdriving) loose, as well as the 2 small phillips screws
4) The problem is that the shaft is supposed to fit tight inside the small gear when assembled, but it no longer does.

Fix A- I have used crazy glue to secure it, but this is dangerous because if too much is used, its very easy for the shaft to now get glued to the grey metal bracket. (The shaft needs to go through the grey bracket, with the gear and washer inside). If you try this way, make sure you have some acetone handy to try and loosen the parts if the shaft siezes to the bracket. You should also do a number of dry runs to make sure you have the parts in the right order. (shaft goes through the top hole in the bracket, through the special washer, and then through the small grey gear. ) the shaft should turn unil it hits the stop created by the washer. Turning in the opposite direction will cause a stop when the other part of the special washer hit the bracket.
Fix B (my preferred way). I take the Shaft (made out of soft aluminum) and mar the shaft near the end in 2 places. I use a old type wire cutter, but you can also use the cutter section on a pair of needle nose, or long nose pliers. I only make small indentations into the aliminum. Be careful, as it is soft, and if you are using something like wire cutters, you can "cut" it rather than just putting small indentations in the shaft. The indentations are to be close to the end of the shaft, where the small gear will wind up sitting. You can now reassemble. Put the shaft through the bracket bearing, through the special washer, and into the gear. You will need to tape the shaft into the gear because the shaft has been marred. You should not have too much play on the shaft moving in and out when you are finished. If you do, you may need to put the blade of a small screwdriver, or a piece of a credit card between the small gear, and bottom bracket plate, and tap the shaft again. Do this a little at a time, as you still want the shaft to turn freely.​

When this is done, the shaft should now sit in its bracket firmly, and not come out again.
Put the shaft and bracket assembly back on the tuning cap by just installing the back flat head screw. Pivot the shaft assembly until it engages the tuning cap gears. turn to one end on the shaft, manually position the tuning cap all open or all closed, and then pivot the shaft assemble to engage tuning cap gears. See it you can turn the shaft and get the tuning cap to travel properly. If it doesnt really travel pivot the shaft assembly out, and position the tuning cap opposite of what you had (either all open, or all closed). Pivot the shaft assembly back down, and make sure the travel is proper. Lastly you will need to reload the 2 parallel tuning cap spring loaded gears, to prevent play in the gears.
Its tricky getting the second screw back in, and the gears need to be in a certail position to do so. Be careful, as you don't want to slip teeth, or lose the spring load while doing this.

You can just put the shaft back in and leave it without securing, but will always have the chance of it backing out, dropping the gear and washer. and loosing tuning capability.
As far as the green glue, acetone on a wood handle Qtip works nice, but only use on metal. Acetone will melt plastic.

 

[ktm-don]

That is an awesome response, thanks Tom B! I was wondering if a small circlip was lost from the shaft, but I understand now that the gear was to be a press fit and stay in place from the friction. The shaft on the HK looks like steel, but I need to get it back on the bench with better tools and lighting, it could be aluminum.

I'll try a bit of acetone on the locking glue, I was concerned about solvents attacking the plastic pulley. As far as I can see loosening those screws and letting the plastic pulley turn on the shaft would be the best way to re-align the pointer to the correct frequency. I may have 'jumped' a tooth on the gear alignment, this is the first time I've powered up this receiver, so I don't know how accurate the dial position was initially.

 

[gadget73]

I had to fix this on a Luxman. Took me several attempts to get it all just right. What I found with that one at least, I couldn't simply re-clock the pulley or string to fix the gear if it was off a tooth. It hit the hard stops on the tuning mechanism before the condenser was fully open or closed. I just had to fight with it until it was all where it went.

probably the same problem on that one. I stuck a C clip in the groove on the shaft to keep it from sliding out and it behaved itself just fine afterward.

 

[audiocrzy]

 

[Pio1980]

I absolutely loathe those tuner drives.

 

[ktm-don]

Well, I could not remove the pulley locking screws in spite of repeated applications of acetone. It's not possible on the HK to remove the bracket screws without removing the pulley. It's currently together mis-indexed, off by many megahertz. I'm thinking about trying to move the pointer. The good news is that the tuner section seems to be really sensitive, picks up low wattage stations with a dipole better than the Nicco that was previously in that spot.

 

[gadget73]

the problem with having it mis-indexed, you probably will not get full travel end to end even if you do move the pointer. At least that was the situation I had with the Luxman with what I expect is a similar mechanical arrangement.

 

[Tom B]

Well, I could not remove the pulley locking screws in spite of repeated applications of acetone. It's not possible on the HK to remove the bracket screws without removing the pulley. It's currently together mis-indexed, off by many megahertz. I'm thinking about trying to move the pointer. The good news is that the tuner section seems to be really sensitive, picks up low wattage stations with a dipole better than the Nicco that was previously in that spot.

Using a qtip, and repeating rubbing around the screws, uusually removes enough that you can remove them. What type of screws are they? Usually just 2 standard Phillips #2 screws?

 

[gadget73]

Probably JIS

 

[ktm-don]

The screws

the problem with having it mis-indexed, you probably will not get full travel end to end even if you do move the pointer. At least that was the situation I had with the Luxman with what I expect is a similar mechanical arrangement.

The screws locking the pulley to the shaft are tiny slotted set screws. It does not take much to damage the screw head slot. I left off the limiting washer, the string slips on the dial shaft easily, so I don't think it will damage the tuning cap by over-driving it. I can tune the whole range, just offset with the pointer position. It was too challenging to get the gear, limiting washer and pulley shaft all aligned while pushing the shaft into place. I might try it again, but my guess is that getting the pulley off the shaft by removing the set screws would be the best bet.

It had crossed my mind to heat the set screws with the tip of a soldering iron to loosen the glue, but it's a tight space, and I was concerned about heat transfer through the metal hub to the plastic string pulley. It just feels like it was built with the idea that it would not ever be disassembled.

 

[gadget73]

oh it was a massive PITA so I know what you're talking about. This one came to me with the dial string off, and I noticed the bits were all out of position when I turned the wheel to set it to whatever end of the dial so I could line the pointer up. I spent a lot of time with it before I figured out where it all had to go, and even more time before I managed to actually get them there.