HP9114A Battery Charging Circuit Board

[aj04062]

I have two of these packs that do not work with new batteries. Something is amiss on the PCAs. These PCAs have 5 total components: Transistor, Rectifier, Diode and two resistors.

The connector that plugs into the drive reads 6V, but the drive will not turn on. If I bypass the board and hook directly to the battery, the drive works so this issue has to be in the board somewhere. It seems to not be getting the current it needs to run the drive.

I have replaces the 6.8V diode and the transistor (TIP41A). The rectifier doesn't come into play here. What is baffling to me is it seems like all the current must run through a 4.7k resistor. This doesn't make sense to me.

Has anyone else had issues with these 5 part charging boards and diagnosed the issue? I have a much more complicated (earlier version I think) board and it works FINE.

I have sketched out the circuit if it would help.

[rprosperi]

(10-20-2017 12:57 AM)aj04062 Wrote:  Has anyone else had issues with these 5 part charging boards and diagnosed the issue? I have a much more complicated (earlier version I think) board and it works FINE.

By coincidence, a friend recently sent me this note about the 9114 battery PCB:

Quote:One of the things on the PCB inside the pack looks like a resistor (or similar device) but is really a 3A fuse. So if/when things don't work well, check on that component. It's easy to spot if you are looking for it, follow the "+" power trace.

Maybe it's the fuse?

[Dave Frederickson]

I've blown the fuse in the 9114 battery pack a few times. See p.22 of the attached schematic.

http://www.hpmuseum.net/document.php?hwfile=2718

The fuse is that thing that looks like a switch.

Note that the fuse in the 9114B is 5 amp. The part number for a replacement fuse can be found here:

http://www.hpmuseum.org/forum/thread-281.html

Dave

[aj04062]

Thanks Gents.

I got it. Does the original fuse have the same markings as 4.7k resistor? That is not helpful. I kept staring at this circuit and was mystified how the heck it would work. Mind you I am not an EE (ME).

A fuse, on the other hand, makes perfect sense!

[Dave Frederickson]

Hi Adam,

The fuse may have color bands like a vintage resistor, but the replacement fuses I referenced are green in color. From the schematic, the fuse is the component connected between pins 3 and 5 of the connector. You should be able to follow the traces back to the fuse. It should measure zero ohms with a meter.

Dave

[aj04062]

Thanks.

Already replaced and working. Easy to trace.