9114 disc drive issues

[Hiwi]

Hi,
i like to share my hardware repair experience. I had 2 issues:

1. The print fuse in the battery case was blown. The drive was completly dead. Connecting a current limiting power supply showed, that there must be a short an the main board.
The 9114 powersupply generates the 12 V for the floppydisk using a pwm. The output drives a Mostfet. It had a short between drain and source. Replacing it (BUZ71) and the disk was working again.

2. Last week, the drive lids up all leds including test, but no spinning of the floppy. The 12V is there VC (5V) and 5V as well. But no 12V on the connector of the floppy. I tested the powerswitiching transistor, everything ok. No activity of the drive controller. The eprom was a bit hot, that was suspect. Signals oK, I tried to read it with epromburner, no error, but no content everything zero. It is an Intel 27128 Eprom. I had only 27C512 on hand, so with a minor change i should work. I burned the Code into the 27C512 and took pin 1 and 17 out of the socket and connected them to ground, pin 14. They are A14 & A15 and not needed.

To my suprise the drive came back to life.

I never had a faulty eprom before.

May be there is a design issue, the VPP line of the 27128 is connected to VCC. Should this not be ground? Actually reprogramming is not possible.



Ralf

   
I have attached the rom file, in case anyone else has the same issue.


  hp9114b.TXT (Size: 16 KB / Downloads: 10)