Oh No another 67 card reader question



#2

To all,

I am working on another HP67 card reader.

I have replaced the gummy wheel - adjusted the fingers so the motor pulls the card through - fixed the clutch - cleaned the keyboard contacts - fixed the cracked posts.

So now I get the card pulling through nice and even at the right speed.

It gives an error on read - no error on write - and yes I will change the capacitor when I can get one today.

BUT - I tried reading the written card in a known good card reader and - error. From previous posts the capacitor only affects the read and the write is ok. I know the write actually writes something but it is not readable in a good reader. I used a good reader to write a dummy program then tried the read in a good reader - OK. Then I used the suspect 67 to write a dummy program and then try reading in a good 67 - error.


Could this still be the capacitor or do I have something else wrong?

Thanks Malcolm


#3

It COULD be one of the capacitors connected to the head circuit (there is one on each head winding), but not likely.

My bet is a bad head winding. There are two windings that should have a resistance of around 40-50 ohms. Also the black head wire should show zero ohms to the metal case around the head. Another posibility is a bad reader chip.

Also, did you clean the head and get those pesky little eyebrow shaped springs back in properly? And are the wires to the head connected to the circuit board. The soldered ones break loose all too easily. The ones that plug into the little connector stake pins love to pop out.

#4

This does _not_ sound like a faulty PSU capactior. My first guess is that you're losing one of the data channels (at least) on both read and write (there are 2 channels/tracks on the card. A pulse on one of them is a '0', a pulse on the other is a '1', basically).
This could be a defective sense amplifier IC (1826-0322 IIRC), it could eb head problems. First check the head connections. Are all 5 wires connected to the card reader PCB, in the right place?
Then check the head windings. You should read about 50 ohms between the blue and orange wires and also between the red and yellow wires. If one winding is open-circuit, you will not be able to read or write.


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