Restoring a HP9830B calculator.

[MattisLind]

Working!

At least I think most of it is working!

Here is the story anyway:

I contacted Tony and received his excellent repair guide for HP98x0 calculators. (His file is in postscript, and is rather small but I converted it to PDF for ease of viewing, then it became huge.) I also downloaded Tony's schematics. While searching the net for HP9830 related material I also found Brent's excellent page on the HP9830 and this HP9830 emulator.

Thanks to Erik I now have the missing DELETE LINE key, thank you very much! BTW. I have spare key tops from a HP2648 keyboard if anyone need keys for a HP9830 (or a HP2648...). Missing only the "5/%" key and one SHIFT. Slightly yellowed though.

Now on to the restoration. After cleaning the unit from plenty of dust I went on following the guide Tony has written, starting testing the insulation of the transformer using a megger. No problems at all. Then (with all cards pulled out except for the PSU module) I powered it up slowly using a variac. Measuring the voltages at the PSU output they all checked OK. But it appears that the +5V switcher need to have some minimum load as well as the 19.5 V output. The latter I would have discovered if I had studied the schematics before I applied power. The 19.5 is generated by a power source circuit and thus will give full raw voltage if not loaded. A 1kOhm resistor did the trick here and using the ROM backplane as dummy load made the 5V produce 5.01V. Since the 19.5V is slaving of the 16 V using a zener, without load on the 19.5V the 16V output started to rise. I presume that eventually the crowbar circuit would hit in, but I never got that far as I used a variac.

Well, with all voltages measuring correctly I just inserted all cards and hit the power on button. I was quite amazed that I got this:

and after pressing random key and finding ENTER I got this:


In a way it was disappointing since I sort of hoped for an interesting journey to repair it... Maybe this shows the quality of old HP products. (My modern HP work PC had the PSU break down after two years. Of course it was just relabeled Chinese stuff inside) The only thing I immediately recognized as failing was the power on indicator in the front.

Of course I haven't tried much yet. Not the tape driver, not the printer interface nor the ROM modules.

Right now I need to assemble the keyboard, then the whole unit.