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mdunn · 04-27-2018, 12:28 PM

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

Steve Simpkin · 04-27-2018, 02:21 PM

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

**rprosperi** · 04-27-2018, 02:59 PM

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.

mdunn · 04-27-2018, 11:42 PM

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.

**rprosperi** · 04-28-2018, 12:32 AM

(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!

mdunn · 04-29-2018, 02:49 PM

(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! :-)

brickviking · 04-30-2018, 12:19 AM

(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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