I cleaned and rebuilt the card reader on this unit, adjusted the reed switches according to the service manual. It now reads well, but sometimes still shows 'error' after a successful read operation. Also, after the card feeds successfully and moves completely through the reader, the motor continues to operate for a second. Any ideas?
Help Appreciated,
Dave
(05-04-2021 07:56 PM)Dreato Wrote: [ -> ]I cleaned and rebuilt the card reader on this unit, adjusted the reed switches according to the service manual. It now reads well, but sometimes still shows 'error' after a successful read operation. Also, after the card feeds successfully and moves completely through the reader, the motor continues to operate for a second. Any ideas?
Help Appreciated,
Dave
It could be that the card sense chip is just "old" and might miss a bit every now and then. This will produce a checksum error.
The motor continues to run briefly after an error condition. This is because of delays written into the HP microcode.
cheers
Tony
Thank you. And thanks for diving into the microcode!
Regards,
Dave
Tony:
I've got a spare sense amp chip. I'll swap them and check.
Regards,
Dave
(05-06-2021 01:13 AM)Dreato Wrote: [ -> ]Tony:
I've got a spare sense amp chip. I'll swap them and check.
Regards,
Dave
Maybe the capacitors as well. if the head is badly worn or dirty it may not be making the best card contact.
cheers
Tony
cheers
Tony
In (vintage) audio equipment like tape recorders, the head becoming "magnetized" is an issue. You would then use a head demagnetizer to improve the audio quality. Could this also be used to improve the reliability of a card reader?
(05-06-2021 10:28 PM)Kees Bouw Wrote: [ -> ]In (vintage) audio equipment like tape recorders, the head becoming "magnetized" is an issue. You would then use a head demagnetizer to improve the audio quality. Could this also be used to improve the reliability of a card reader?
Can't see why not, it the same mechanism.
cheers
Tony
Thanks for the suggestions. I used my old head demagnetizer during the rebuild.
I'll check the caps. I've learned that tantalum capacitors have a limited life, albeit longer that regular electrolytics.
Regards,
Dave
It was the caps. Tx for the reminder about these! Interesting to note that all the caps I removed tested fine on my capacitance meter.
I'm seeing cap problems in some HP25s I'm working on. The caps test fine in the meter, but don't work well, or at all, in the internal power supply.
Regards,
Dave