HP67 card reader



#7

Is it possible to find micromarbles which actuate the switches of the card reader on the HP67 ?. She were lost during an "open heart" operation.
This call is for a friend without Internet.
Many thanks for your help. Marcel


#8

I don't know about replacements, but in the past, out of desperation, I have vacuumed the area with a new bag in the vacuum cleaner, then gone through the bag to try to find lost tiny items.

The balls look like tiny versions of the ones in roll-on deodorant. I wonder if ball bearings are ever made out of plastic - maybe for quiet operation under a light load.


#9

(:o ) Sounds reasonable to me.

I am very careful, but recently I got distracted when trying to repair my one and only ever attempt so far of an HP15C. It had it's keys glued by a coke-a-cola having been dumped directly on the keyboard and it was soaked in very nicely.

Have you ever tried to find those two little springs on tightly woven multi-colored carpet(speckled colors of gray to dark brown only. No blues, greens, or reds)?

If it hadn't been for the recent purchase of a torx T-6 with an extremely powerful magnetic charge I would have never found them. Do you have any idea how many times you can move a T-6 across an average area of carpet, very slowly and very carefully?

Doug


#10

You can get exact replacement switch activation balls from www.smallparts.com. They are 1/8" Delrin balls (4 of them used in the card reader) part # BDLR-2 @ $2.00 for 10 of them. (They don't sell the little pin roller that is directly under the r/w head.) You can also use the .005" beryllium copper sheet that they sell (part # BCS-005) to make card contact springs if you lose them.


#11

That's great to know! I just got a 67 and a 97 and working on those card readers is one of the "funnest" calculator activities I've had. BTW I test ran the motor from one of them, out of the assembly, with a Classic battery and it only draws 13 mA. With a little finger pressure on the end of the shaft it rose to 50 mA. This is no more power than an LED, it's amazing to me that it uses so little current (although I have no experience of tiny motors, maybe this isn't so amazing.)


#12

Once you get it in the mechanism the motor can draw 200mA (with an even larger startup pulse). The HP97 service manual mentions how to set the tension of the elliptic cam shaft to the roller by measuring the current with a card stalled in the reader.

#13

I've had luck using steel ball bearings in the card readers. I was actually skeptical at first because I thought that the steel balls might be slightly magnetic and cause problems on the magnetic card strips. Has any body else tried using steel ball bearings which are easily obtainable in the USA?


#14

Most stainless steels are non-magnetic... so look for stainless balls. I would worry more about steel causing wear to the cards and the switch contacts. I would highly recommend plastic balls. They are cheap and readily available.

#15

Hi all: Ellis, david, Doug, Katie, Erik :
Thanks for your help. I will not use steel but plastic balls.
I use always digital macrophoto before repair because a connection wire is possibly quick broken.
Best regards Marcel


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