HP 67 Card reader still no go



#14

I got an HP 67 on eBay a while back. Works fine except for the card reader. Cards would not go through, motor would speed up and slow down, dragging.

I read and performed the procedure for replacing the roller with a piece of vinyl tubing. The original roller did not look "gummy" but I replaced it anyway. The heads and the rest of the inside all looked clean. And I pulled it off without losing any of the pieces.

Now the cards move smoothly through the reader, the motor moves at a constant speed that sounds good, but the display still reads "Error" every time.

Any suggestions? I've read that silicone tubing is better than vinyl, and ordered some. But since the card motion sounds smooth I doubt that it will help.


#15

Are you trying to read or write a card? That is are you sure the card has something on it? Try writing a card and then reading it back.

rdb.

#16

The problem is either a switch problem or card reader chip problem . There are gold plated finger switches that turn the motor on/off, and tell the card reader cpu whether a card is protected or not. If these swiches are not set properly, you will get that error. I usually look at the keyboard pcb and trace the points that the finger switches touch and then use an ohm meter to check switch contacts as I insert a card. If one is out of adjustment, you tighten or loosen the small screws that retain the switches.Another way to check the switches is to insert a card( with card reader assembly removed) and look at the relative hieghts of the fingers. The first finger that operates as the card is inserted is the card reader on switch. Since that is working properly, try to adjust the heights of the other switches to match that.
The speed at which the card goes through the calculator could also be the proble. There is on some HP-67s a 1-turn pot for adjusting the card speed. I usually set it in the middle position. There is also a nylon eccentric shaft that serves as the axle for the wheel. By turning this shaft either clockwise of anticlockwise will change the speed of the reader because it adjusts the grip of the wheel and card.

Hope this helps.


The card read crc chip is on the main cpu board by the way.

#17

You should also check the five wires from the read write head to the circuit board. They are VERY fragile and either break off (if soldered down) or pop out of their socket pins (on later models). You DID write down their positions before you started working on it didn't you? This is a VERY good idea... it had saved me many, many times.

Also I beleive that the CRC chip is on the long, thin little circuit board that plugs into the main cpu board. The head connections are next to it. Not all heads have the same color code and different versions of the card reader board have slightly different layouts.


#18

The chip at the end of the long, thin circuit board is marked 1826-0322 which, according to the HP-97 Service Manual, is just a sense amplifier. The HP-67 doesn't have a separate Card Reader Chip (CRC), these functions I believe are integrated into the main CPU.

I also have an HP-67 that has a similar problem. Experimenting with it, I found that it can write cards fine (and these cards are readable on another HP-67), however, it cannot read cards. The outputs of the Sense Amplifier appear normal on a 'scope, which leads me to suspect that at least in this case, it's the main chip that went bad (although it is also conceivable that I have a faulty ROM chip.)


Viktor


#19

I believe the crc chip is the biggest one on the HP-67 cpu board. It has the same part # as the one on the HP-97. The HP-97 repair manual lists this as the crc chip.
I have replaced this chip in the past on HP-97s that would disply "error" when trying to read a card, and have fixed that problem.


#20

Erik,

You know what, you're absolutely right. I always boldly assumed that the 'big chip' on the HP-67 CPU board is in fact its main CPU; it never occurred to me to cross-check its part number. Thanks for correcting me! It also gives me hope that I'll be able to bring back one of my HP-67s to life with relative ease (if you call desoldering a large chip like that easy, that is!)


Viktor

#21

One potential problem that can arise is replacing a drive wheel with rubber that is a different diameter than the original. The card speed will not be the same. If the new rubber is larger than the old, the card will move too fast and the last few bits will fall of the end of the card. HP uses a "select value to fit" resistor to control the motor speed. Its a real pain to adjust as you have to unsolder it and replace it with another one. I had one unit that I fixed by replacing the drive rubber with a slightly undersized piece of black neoprene fuel line.

It really helps to have access to a magnetic viewer or magnetic "developing" fluid to see the data tracks on the card. I think Edmund Scientific still sells the magnetic developing fluid. I've seen one brand called Mag View. Another is called Mag See.


#22

The later HP-67s hasd a one turn pot for the motor resistor. I wish they had doine that on all of them.

#23

Thanks to all the suggestions for repair of this 67 card reader.

To answer one question: I get "Error" both when trying to read and write cards.

I cleaned the heads with tape head cleaner and replaced the roller again, this time with silicone tubing instead of PVC, but that didn't help.

I think the problem is with the switch contacts. I traced them to pins 14, 16, and 17 of the CPU board and measured them with a voltmeter as I ran a card through the reader. Only one of them showed activity. I tried bending the contacts. I also cleaned them and the PCB pads with acetone, but neither helped.

Next I think I'll try fiddling with the screws that adjust them.


#24

If you do not see all three switches making contact then you do have a problem in the leaf spring contacts.

The first switch is the card detect switch. It starts the motor. Sounds like it is OK.

The other two are the write protect switch and the head enable switch. Write protect is sensed close to the beginning of the card cycle about the same time as the card edge.

The head enable switch is sensed after the card has started moving. It is used to trigger the read/write electronics. These switches are all activated by the card pressing on those little nylon balls.

If you dont get a head switch signal, typically the display wont go blank as the card feeds in and you may or may not see the ERROR indication (depending upon the machine firmware version). HP-65's show an error by flashing the display.

#25

Thanks again to all your suggestions. I got it working!

I turned the adjustment screws about 1/8 of a turn, enough to get the springs to make contact with the PCB. Operation was a bit erratic first. I could write cards OK, and read the back in, but could not read the pre-recorded cards. But after some use, and with no further adjustment, it started working better. Now I get an occasional error but have always been able to read the card on the second try.


#26

Two things to try for the erratic reads: first run the cleaner card in the standard pac through it a few times.

Also you may need to adjust the tension on the eccentric cam pin. This is the nylon pin that serves as the axle to the drive roller. Rotating it adjusts how hard the card is gripped by the roller. You can get to it without disassmbling the reader. I use a small screwdriver as a lever to tweak it when it is in a near vertical position. When it is more horizontal I use a right angle dental pick.

One final problem could be a slipping motor clutch. This is the friction fit joint between the motor shaft and the worm gear that drives the reader wheel. There is a nylon insert in the end of the worm gear that either clips or begins to crumble. I usually wind up using a SMALL drop of black CA glue to fix the problem.


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