HP97 Card Reader Motor Replacement?

[GanjaTron]

Hi everyone,

I have refurbished the card readers in my two HP97s (gummy wheel --> tygon or silicone tubing), but one of them has been seriously acting up recently. It sporadically stalls and won't start up at all, or run very slowly, sounding severely laboured and irregular.

After removing and hooking the motor up to a PSU, I immediately noticed it squeals and vibrates intermittently. If I tap or shake it, the squealing stops briefly, only to resume after seconds. In contrast, the motor in the working card reader is practically silent. I compared the current draw of both motors with a bench supply at 2V and got the following (note the motors are from different manufacturers, both Swiss):

Escap (squeals):
Outside card reader: 20-25 mA (intermittent), 50-60 mA (squealing)
Installed, unloaded: 110-120 mA (240 mA startup!)
Installed, card loaded: 240-250 mA (!)

Maxon (silent):
Outside card reader: 15-20 mA
Installed, unloaded: 20 mA (25 mA startup)
Installed, card loaded: 160 mA

According to the service manual, the motor shouldn't draw more than 50mA unloaded, and 180 mA under load, so the Escap appears to have worn bearings or brushes, on top of which it draws an almost tenfold current just to get going!

Interestingly, if the motor is installed in the card reader and powered by the calc, it will only start up when a small resistance is placed in series with one of the motor leads; I noticed this when I hooked up my multimeter to measure current. The motor will then sporadically come up to full speed for 2-3x successive card reads before slowing down and stalling again for a while. Once stalled, the voltage across the motor is just 0.1V or so (instead of >2V) before the calc gives up and issues an error. That leads me to also suspect a fault with the Sense Amp on the card reader PCB, or can the worn motor bearings alone cause this behaviour? (I haven't tested the Maxon in the faulty card reader yet -- TODO).

So in a nutshell: has anyone had problems with their card reader motor and found a viable replacement? Furthermore, has anyone experienced flaky motor voltages coming from the Sense Amp?

Thanks for any hints,

--Roland

[Zaphod]

(04-30-2018 07:34 PM)GanjaTron Wrote:  I have refurbished the card readers in my two HP97s (gummy wheel --> tygon or silicone tubing), but one of them has been seriously acting up recently. It sporadically stalls and won't start up at all, or run very slowly, sounding severely laboured and irregular.

After removing and hooking the motor up to a PSU, I immediately noticed it squeals and vibrates intermittently. If I tap or shake it, the squealing stops briefly, only to resume after seconds. In contrast, the motor in the working card reader is practically silent. I compared the current draw of both motors with a bench supply at 2V and got the following (note the motors are from different manufacturers, both Swiss):
So in a nutshell: has anyone had problems with their card reader motor and found a viable replacement? Furthermore, has anyone experienced flaky motor voltages coming from the Sense Amp?

Thanks for any hints,

--Roland

Speaking generally that just sounds like a dried out bronze bush at either end of the motor.....
You need to apply a tiny drop with ideally a syringe applicator (Like one of these: https://www.amazon.com/slp/oil-bottle-wi...fyuvh9w56h )

Let it pull into the bearing bush gradually by capillary action.... and you may find that's all the problem was.
The only other problem micro motors suffer from (usually) is brush/commutator problems .... brushes wear out or the commutator face tarnishes producing random dead spots because the brush pressure isn't usually very strong.

The pulley end is usually easy as it's visible, the brushes end needs you to carefully remove the end-cap... but you need to work out how to protect the brushes as you remove the end-cap. Manufacturers usually hold the brushes apart via holes in the end-cap to get them safely over the end of the spindle and on to the commutator area.

Squealing is undoubtedly the bushes dried up though... the spindle will 'rattle' at high frequency in the bush.

[GanjaTron]

Hi Zaphod,

thanks for chipping in. I did drop some teflon lubricant down the spindle (albeit on the end of a toothpick, lacking a syringe), and let that work in. That brought partial success to the effect that the squealing is now intermittent, so after a few days I followed up with low viscosity oil specifically for precision mechanisms, and let it sit on end overnight. That made no difference at all. I hesitate to dump something more aggressive into it, as I expect the additives may break down any insulation inside.

I have no idea how to open the motor up. There are four tiny holes around the connector (brush?) end of the motor, but I can't tell if these are hex screws or recessed rivets of some sort. Could post a pic if that helps. Btw, the Maxon motor is different: it has a red plastic end cap that wraps around the side. The end cap on the squealy Escap is flush.

I guess it's easier to pacify a squealing kid...

--Roland

[Zaphod]

Photo's would be good

The four holes could be anything, even be the holes I was mentioning that hold the brushes apart on assembly.

[Warbucks]

For what it's worth, silicone and/or teflon based lubricants prevent other oils from bonding.

JW

[GanjaTron]

(05-01-2018 05:56 AM)Zaphod Wrote:  Photo's would be good

The four holes could be anything, even be the holes I was mentioning that hold the brushes apart on assembly.

Hi Zaphod,

here's a couple pix showing the four holes, which don't appear to be hex screws after all. They simply look like recesses in the rim of the gray plastic end cap. There's also a glued black plastic cover underneath the terminals which, when removed, reveals a spindle sandwiched between two flat contacts. I take it these are NOT the brushes, right? If they are, should I apply oil or contact cleaner to the exposed spindle? If not, how would I go about disassembling this thing further (i.e. removing the end cap)?

                   

This thing shrieks so bad beyond 2V, it's actually painful!

--Roland