HP67 repair squelch

[murphy9]

Help - one of my HP67's has become a squeaky mouse!

Any clues to why I'd get a squelch on an HP67. Power up with new battery and get the squelch/squeak, then error. The motor from the mag strip also powers up for a second.
Could be a sensor on the card reader. I'd be interested to see if anyone has any similar experience before I start taking it apart and probe things.

Many thanks

[murphy9]

OK - thanks to the internet I suspect a clutch issue - question superglue or something else. What is the consensus ?    

[Paul Berger (Canada)]

I think you do have a sensor issue if the motor runs when you turn on the 67, that does not happen on mine unless there is a card inserted when I turn it on. This would suggest that the card inserted switch is "stuck" since these are normally closed switches operated by little nylon balls, so it could be just contamination on the circuit board.

[teenix]

(01-15-2020 10:38 AM)murphy9 Wrote:  Help - one of my HP67's has become a squeaky mouse!

Any clues to why I'd get a squelch on an HP67. Power up with new battery and get the squelch/squeak, then error. The motor from the mag strip also powers up for a second.
Could be a sensor on the card reader. I'd be interested to see if anyone has any similar experience before I start taking it apart and probe things.

Many thanks

The HP-67 microcode tests the card status just after switch on. If it "sees" a card in the slot, it will turn on the motor and wait to see if the card is ejected in a certain time. If not, the motor is switched back off and an error is displayed. If so, the motor is switched off and life is cool.

It's possible that...

the nylon ball has foreign matter keeping it held against the card switch,

corrosion anywhere along the circuit path from the switch contact to the CRC chip,

the switch needs adjusting,

something jammed in the card reader slot,

or worst case, the CRC chip has failed.

A word from the once bitten, twice shy. If card reader disassembly is required, this should be undertaken with care. The small parts are experts in the art of disappearing. Also be careful if you really have to adjust the switch contacts, it is easy to overdo it.

Hopefully just a clean up and it will be fine.

cheers

Tony

[murphy9]

thanks all for the tips.

Teenix - yes - I spent 2 weeks trying to find the nylon bearing after my last (successful) rebuild.

Any thoughts on the clutch question - super glue or new rubber/plastic shroud (and how the heck do I source that?).

[teenix]

(01-16-2020 06:11 AM)murphy9 Wrote:  thanks all for the tips.

Teenix - yes - I spent 2 weeks trying to find the nylon bearing after my last (successful) rebuild.

Any thoughts on the clutch question - super glue or new rubber/plastic shroud (and how the heck do I source that?).

I found an easy way to fix the drive coupler, although I don't think this solves the motor start error.

See Thread: HP97 The journey begins Post #18
(Sorry don't know how to link it.)

If you want one but can't make it yourself, I'll post one to you.

cheers

Tony

[ijabbott]

(01-16-2020 07:15 AM)teenix Wrote:  I found an easy way to fix the drive coupler, although I don't think this solves the motor start error.

See Thread: HP97 The journey begins Post #18
(Sorry don't know how to link it.)

HP97 The journey begins - post#18

[murphy9]

Many thanks - this looks like something I can get easily here

https://www.jaycar.com.au/50-ohm-rg58-c-...e/p/WB2012

Will have a 'play'

Backup will be superglue :-(

Weekend and Magnifier required I think.

[rprosperi]

(01-16-2020 07:15 AM)teenix Wrote:  (Sorry don't know how to link it.)

You can click on any post number in the upper right corner of each post (in this case, click on the "#18" of that thread) and it will make that post the top of the displayed window and adjust the url in the browser address bar so you can just copy it. It took a long time to find this when MoHPC switched to this now forum s/w, and it seems it is not always available in other versions of myBB.

[grsbanks]

Or you can right-click on the post number and select "Copy URL" or "Copy Link" depending on the browser that you're using. Saves having to change your position on the page and copy the URL from the address bar.

[teenix]

(01-16-2020 04:00 PM)grsbanks Wrote:  Or you can right-click on the post number and select "Copy URL" or "Copy Link" depending on the browser that you're using. Saves having to change your position on the page and copy the URL from the address bar.

Doh!

I waved the mouse over the "Post" part of the text, and not seeing the cursor change I didn't think it was a link.

Thanks for the replies.

cheers

Tony

[teenix]

(01-16-2020 12:19 PM)murphy9 Wrote:  Many thanks - this looks like something I can get easily here

https://www.jaycar.com.au/50-ohm-rg58-c-...e/p/WB2012

Will have a 'play'

Backup will be superglue :-(

Weekend and Magnifier required I think.

Speaking of play, I forgot to mention there that it is easy to make the coupler a bit wider than normal thinking perhaps that it will have a better grip on the motor shaft.

However it should be kept to the same width as the normal coupler because the motor shaft needs a small amount of side play so that the worm gear meshes properly with the drive wheel. After re-assembly a longer coupler may put pressure on the motor shaft causing drag and high motor current.

cheers

Tony

[burkhard]

(01-15-2020 01:46 PM)murphy9 Wrote:  I suspect a clutch issue

It's not a clutch, but a coupler. If it acts like a clutch, it has failed. There should never be slippage.

[Geoff Quickfall]

Correct, it is not a CLUTCH. It is a dampening couple. It dampens any vibration from the motor to the pinch roller.

Crazy glue works but removes the dampening portion, is temporary and if there is any vibration in the system, causes read and/or write errors.

It’s akin to calling heat stakes ‘rivets’.

The squeal is typically from the dampening couple slipping on the motor shaft as the natural rubber couple decomposes in the same way as the pinch roller decomposes over time. The couple has two inner diameters; one for the worm gear and one for the motor shaft.

There are a few fixes out there for this. Just google them.

Geoff

[teenix]

(01-17-2020 02:55 PM)burkhard Wrote:  It's not a clutch, but a coupler. If it acts like a clutch, it has failed. There should never be slippage.

The job of this item is to transfer the motor shaft rotation to the worm gear drive, ie - a coupler.

I suspect some head scratching went on when the first motors arrived to test in HP's labs. With such a small diameter motor shaft, I'm guessing it would be difficult to manufacture screw mount couplings or machine it in any way for keyways and the like. The end solution was simple and elegant and does its job well.

The contact area between the motor shaft and the coupler is very small so it can slip under high load. However, if the coupler is in good condition, a card jam can cause motor stall without slippage. The microcode senses jams (CRC for 65) and hopefully turns off the motor before damage is done.

The drive wheel can slip on the card if worn. This is also allowed to occur as it is written up in the service manual. For example, holding the cards while testing for motor current. In this case the drive wheel is most likely slipping otherwise it has to be the coupler. I personally wouldn't do this test as the coupler may let go on the shaft and cause wear.

Vibration may be an issue but I don't think it is quelled by the coupler as it is made of quite dense material and as mentioned, the contact area is very small and it is in tight contact with the shaft. The shaft turns at 10,000rpm and the data transfer rate is about 1KHz. Unless the vibration is large I can't see much of a problem. I think the main source of vibration is not from the motor itself, but from the rpm reduction mechanism which is actually on the card side of the coupler. The chosen worm gear drive is the simplest reduction method with just one helical gear and therefore reasonably quiet with minimal backlash.

These mechanical marvels have been around for 46 years now and I'm sure some vibrate a lot more than when originally manufactured, but they still work. I've even fitted a dodgy coupler and it vibrated quite a bit, but still worked.

Worst case vibration might cause card flutter against the head but that would have to be pretty bad.

I think card azimuth alignment would be a worse condition, and could be caused by weak or missing card side load springs.

Just an opinion :-)

cheers

Tony