Comments very welcome: HP 25C shows *some* signs of life… Occasional zeroes on display. Voltages present, semi-clean (what are typical noise levels? I threw extra tantalum across the 6V – reduced noise, but otherwise, no help). Clocks present. POR seems to POR. Serial data bus shows continuous repetition of the same word (though the signal looks very odd – the lower quarter or so is decidedly not a clean digital signal – is THAT normal?). The SYNC line has a problem – all I see there are +/-900 mV spikes. Makes me think the processor is toast.
Thanks,
Michael
It sounds like a damaged ACT chip. This is common on theses Woodstock and Spice models due to trying to operate them with the AC adapter without the battery installed (or a bad battery). If this is the case, there is now a great repair option
http://www.panamatik.de/html/hp_calculat...r_kit.html
Though Steve's recommended solution is far better, and I also strongly recommend it (or even better, Panamatik's Woodstock Low-Power), for the record there is also an option of replacing the bad ACT chip with another from a working machine, which can be taken from any Woodstock including the HP-21 which is more available and typically cheaper to purchase. Though I generally avoid recommending destroying a working vintage machine, sacrificing a 21 to restore a 25 can be justified IMHO.
But I too say you should go with Panamatik's kit, it provides you with a much better machine, and no Woodstock would be harmed in the process.
Thanks for the tips. Cool upgrade board! But I'm just not that ambitious. As for cannibalizing an e.g., HP 21...weird...they go for such a wide range on eBay...so, maybe – if I can get a very cheap one. But given my 25 is also missing the case back, I doubt I'll expend much more effort, unless...a 21 has the same case! :-) Though if I ever do get the 25 working, I might make a wood back for it.
(04-27-2018 11:42 PM)mdunn Wrote: [ -> ]Thanks for the tips. Cool upgrade board! But I'm just not that ambitious. As for cannibalizing an e.g., HP 21...weird...they go for such a wide range on eBay...so, maybe – if I can get a very cheap one. But given my 25 is also missing the case back, I doubt I'll expend much more effort, unless...a 21 has the same case! :-) Though if I ever do get the 25 working, I might make a wood back for it.
Good news! The back of all the Woodstock machines are the same; certainly on the outside, and I believe on the inside as well, so if you locate a good '21 donor, you can migrate the ACT and use the back too.
Though I have to admit to wanting to see a Woodstock with a Wood back!
(04-28-2018 12:32 AM)rprosperi Wrote: [ -> ]Though I have to admit to wanting to see a Woodstock with a Wood back!
Or............ Concrete! :-)
(04-29-2018 02:49 PM)mdunn Wrote: [ -> ] (04-28-2018 12:32 AM)rprosperi Wrote: [ -> ]Though I have to admit to wanting to see a Woodstock with a Wood back!
Or............ Concrete! :-)
I know! Lego!!! Or ....... dried-up plumber's putty.
Naah...
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