HP82143A Repair - Buzzing While Powered On

[cesarb94]

Hello,

So I have an 82143A that currently powers on and is recognized by the calculator when accessing CAT2.

The problem is that when it is powered on there is an audible buzzing sound coming from the power supply circuit at all times. Also, when I try to print something from the calculator, or hit the paper advance key, another sound is emitted by the motor for a brief moment, stops, and then the message "Printer Error" appears on the calculator screen. The motor does not move at all when this happens.

I've been running the printer with a set of NiMh AA batteries, since I'm still waiting for a refurbished pack to arrive. Therefore I do not know if this is a problem with the printer itself, or the method I'm using to power it up.

I've found the service manual. I'll probably start probing around, but if anyone had a similar issue or have a guess on where to start looking, I appreciate any information.

Thanks in advance.

[teenix]

Hard to say, but maybe the power supply sees a heavier load than normal by some fault which in turn is causing the oscillator to work harder and be audible.

Is any part of the circuit getting warm to the touch?

cheers

Tony

[cesarb94]

Hi Tony,

Sorry for the late reply.
No, I've let it on for a few minutes again, but couldn't find any hot spot on the circuit board, at least nothing warm to the touch.

I'll probably work on it this weekend.

Best regards.

[Kostas Kritsilas]

Its possible the cores in the inductors used in the on board dc-dc converter are vibrating. Common heard these days in PC power supplies, especially laptops, but not unheard of in days past, either.

[cesarb94]

So apparently the printer actually works, the real problem was a jammed motor. I've removed it from its mount, spinned the rotor by hand a few times and now it's free and the printer is working. However the buzzing sound is still present and it it's volume gets higher when sliding the intensity selector towards "dark". I've replaced the small capacitor from the power supply circuit but that changed nothing.

[teenix]

Maybe try when you get the D cells. They have a higher current rating. The AA batteries might not be quite up to the task when printing.

cheers

Tony

[cesarb94]

Hi Tony, forgot to mention, In the mean time I've rebuilt a battery pack with SC cells. So this buzzing happens with either batteries, AA and SC.

I've also tried to poke every component to see if the sound changes pitch, but no luck.

Best regards.

(08-24-2021 12:19 PM)teenix Wrote:  Maybe try when you get the D cells. They have a higher current rating. The AA batteries might not be quite up to the task when printing.

cheers

Tony