HP 9114A Disc Drive Problem


I have one HP 9114A which work flawlessly. Then I got a second one which supposedly has a weak battery. So I tried to power it up with the good battery of my first drive. It came on but didn't work. Now both drives don't come on with either battery pack. Seems as something has fused inside the battery packs. Any ideas are much appreciated. Daniel



I'm not sure about the details, but the HP9114A Operator's Manual, p. 2-9, mentions that the batteries are fused. There's no mention for the fact that they may be repaired.

If you are going to open the pack, please, do it on your own risk. I'm just passing the same information I was given, O.K.?

Best regards.


Thanks Luiz,

I've opened the two batteries and found out that they have different PCBs. One battery is of Type A the other of Type B (more comploex PCB). But I didn't see any element on them which could fuse. So I took the good byttery of Type B to the Type A battery which now let's me power up both drives. So now I have another problem. I tried to format a Maxell DS,DD 1.0 MB diskette whith my HP41CX. When I do NEWM 128 it formats nearly the whole diskette and then stops with message NO MEDM. Strange and it does it on both drives. What's going on here - this has once worked. But I must say that I haven't used the good drive since about one year. Do I use the right type of disks?


I'd try using a floppy drive cleaning disc. I've found it has made my drives DRAMATICALLY more reliable :-)

On another point...

Would it be possible for you to scan both PCB's (both sides too)? I'm interested in the difference between various charger units HP used.

My email address is steveh at iinet dot net dot au.

From memory there was a fuse in mine... I'll try to check when I get home.


I have taken snapshots of the PCBs and have sent them to Steve. Anyone else interested just let me know.


Hi Daniel,
there IS a fuse on both PCBs. Referenced to the PCB of type B the fuse is the part located dirctly on the left of the 5 Pin connetor. It is eihter labeled 5AF or it looks like a resistor - body green with code red red black(? I dont remember exactly) green on it. IT IS A 5A QUICK ACTING FUSE. When I come home this evening I can send you photos of both and I will verify if the black ring(in the code) is correct.
Kind regards, Andreas


Thanks to all for your help so far. I'm sure I'lll be able to repair the power supply issue with the help of the photo by Andreas. Now there's still the problem with formatting the diskettes. Just not sure if I'm using the right ones. Besides that has anybody use the DOS program SYDEX to format diskettes?


Besides that has anybody use the DOS program SYDEX to format diskettes?

Hello Daniel,

I did use CopyQM, TeleDisk, FormatQM(?) and others ... 10+ years ago.

I should be able to find them in the floppy stack down in the basement.
What's your question about these programs?




I found the fuse on the Type B PCB to be broken. I'll possibly replace it with something similar. I also found out that I was a bit too impatient. The formatting problem has disappeared after fully charging the battery. Now both drives work properly. I've also tested writing a HP41 program on one drive then reading it on the other drive and vice versa. Thanks for all your help.


Hi, Daniel;

good news from you! Congrats.

One information I took from the HP9114A Operator's Manual that I found interesting: use the AC adptor as many times as you can. Using the HP9114A with the AC adaptor directly connected to the AC outlet and to the batteries is sort of good practice.

Despite finding it strange, I've been keeping this procedure.

Best regards.


Hi Daniel,
I just sent you the snapshots - I know you do not need them anymore - with some comments and hints. In a few days I can send you the schematics too, if you are interested. Just let me know.
Kind regards, Andreas


I have replaced the 5 amp fuse in the charging circuit and have a question regarding the charging cycle. When charging partially discharged battery the voltage measured at the battery will slowly increase as the battery is charging. When the battery is completely charged the charger output voltage will slowly rise to 8.05 volts and then drop to 7.5 volts in a continuing cycle (no load on the battery or charger) When the voltade is at its highest a green LED will turn on on the PCB and apparantly cycle on and off as the voltage changes. It is a type B circuit board. I have not checked to see if this occurs with a load on the battery. I was just wondering if this is normal for this circuit.


Hi Dale,
for me this sounds like a kind of 'trickle charge mechanism'. But I wonder if the voltage is correct. When you read datasheets and application notes of lead acid batteries(there is good info at Hawker's website) you will find(for a 6V battery) 7.5V max. voltage for cyclic use and about 6.9V max. voltage for standby use. But in all cases 7.5V is the highest allowed voltage. So, may be there is something wrong with the charger circuit? Another thing is the little NTC on the PCB. May be this resistor is a built in temperature compensation for the 'end of charge' voltage. I have a netlist of the PCB. I hope to have a schematic of it in a few days. Then, perhaps I can tell you more.
Kind regards, Andreas


Hi Dale,
I made some measurements on the PCB of my Battery unit. It is toggling in the same way you described. The voltage readings are 7.81V max.(LED switches on) and 7.33V min.(LED swithces off). Both voltages drop when the NTC is heated, for example by hand.
It is a trickle charge!
The schematic is ready. I have to make it a bit more 'readable' and then pdf it.
Do you want the schematics?

Kind regards, Andreas


I am interested in the schematics for the charger. My main concern was that I did not damage the circuit board when I replaced the 5 amp fuse. This seem like an unusual way to implement a trickle charge.
Thanks for the information!!
Dale Richmond


Hi Dale,
<<This seem like an unusual way to implement a trickle charge.>>
You are right. It is a 2 point regulation - like the basic heating regulation at home - resulting in a mean voltage of about 7.5V.
Regards, Andreas


You need to cover the hole in the corner of double sided disks for them to be recognized by the hP drive. This just happens to be where HP placed the optical sensor for detecting an inserted disk.

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