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+--- Thread: HP 2648 running at 50 hz (/thread-16707.html)
HP 2648 running at 50 hz - locsharp - 04-20-2021 09:53 PM
Hello,
I got an HP2648 terminal from the US.
I read in the manual that if you run the machine with 230V 50Hz power ( like we have in Europe ) beside changing a couple of fuses , you have to also replace the display timing card crystal.
The one required is 17.55 Mhz but I am not able to find this anywhere.
Is there a way to solve this ?
Thanks
Ste
RE: HP 2648 running at 50 hz - BobVA - 04-22-2021 01:04 PM
Nice find!! And welcome aboard!
Options are:
- Look for a broken terminal to salvage the crystal. Easy, but not very predictable :-) A quick google makes me think that frequency wasn't in common use for other devices, so it may take awhile to turn one up.
- Get a bespoke crystal made. There's still some places that do this. This thread on the EEV Blog has some useful links.
- Use a programmable synthesizer IC to generate the frequency. This isn't rocket surgery, and it's inexpensive, but you will need the schematics and some electronics experience / tools to figure out exactly how to do it. You'll need to determine what kind of signal that crystal oscillator circuit generated (e.g. voltage, etc), duplicate it, then inject it where the terminal electronics expect it. Radio amateurs have to do this frequently since the crystal market dried up, so google something like "replace crystal with frequency synthesizer" and you'll probably turn up a lot of information.
Schematics and lots of technical documents for the 2648 are available at Curious Marc's site among others.
I'd also ask around on the Vintage HP Computer Group at groups.io. Somebody there may have solved the problem or have the crystal in their junk box.
Also check maybe check around on some of the links at The 9845 Project
RE: HP 2648 running at 50 hz - Martin Hepperle - 04-22-2021 03:15 PM
maybe look here - they seem to have the desired frequency:
https://www.surplussales.com/Crystals/Crystals-6.html
Martin
RE: HP 2648 running at 50 hz - locsharp - 04-24-2021 06:55 PM
(04-22-2021 01:04 PM)BobVA Wrote: Nice find!! And welcome aboard!
Options are:
- Look for a broken terminal to salvage the crystal. Easy, but not very predictable :-) A quick google makes me think that frequency wasn't in common use for other devices, so it may take awhile to turn one up.
- Get a bespoke crystal made. There's still some places that do this. This thread on the EEV Blog has some useful links.
- Use a programmable synthesizer IC to generate the frequency. This isn't rocket surgery, and it's inexpensive, but you will need the schematics and some electronics experience / tools to figure out exactly how to do it. You'll need to determine what kind of signal that crystal oscillator circuit generated (e.g. voltage, etc), duplicate it, then inject it where the terminal electronics expect it. Radio amateurs have to do this frequently since the crystal market dried up, so google something like "replace crystal with frequency synthesizer" and you'll probably turn up a lot of information.
Schematics and lots of technical documents for the 2648 are available at Curious Marc's site among others.
I'd also ask around on the Vintage HP Computer Group at groups.io. Somebody there may have solved the problem or have the crystal in their junk box.
Also check maybe check around on some of the links at The 9845 Project
Good points.
Thanks very much for the info.
RE: HP 2648 running at 50 hz - locsharp - 04-24-2021 06:58 PM
(04-22-2021 03:15 PM)Martin Hepperle Wrote: maybe look here - they seem to have the desired frequency:
https://www.surplussales.com/Crystals/Crystals-6.html
Martin
That's great !!
I will order some.
Thank you.