I could have some help figuring out how to upgrade it from a 16Mhz 386 CPU to a 33Mhz 386 CPU and how to find the parts I would need and I know it is one where the processor is on an expansion board and here are some pics of the insides:
and some more Photo's:
The Last few pics:
It also has a 5.25 Disk Drive and a 3.5 Inch drive and no HDD
You need the CPU swapped to something 33MHz rated to make sure it works at all, but then the actual frequency at which it'll run is decided by the mobo clock. Which sometimes can be replaced if it's a crystal generator in 4-pin metal package (and I would assume it is for this mobo). But here's the main problem - will the rest of the mobo be able to keep up. And I wouldn't bet on it I'm afraid... but you can try a lower overclock first, say install 38 or 40 MHz generator (the CPU clock is half of that). If you are lucky the original will be socketed, if not you have to desolder it and preferably put a socket there so you can swap and try easier. Do note, the final choice might need a zip tie to hold it in place, these things often like to work themselves out of the socket due to vibrations, that will prevent mobo from booting obviously and a few years from now it can happen to you - and you'll forget about the swapped generator and start poking everything else.
BTW that's a nice B1 stepping 386, too bad it's sigma-sigma. Still, plenty of interesting CPU bugs on it.
EDIT: PS, what brand of 5.25" floppy drive is that? Looks a bit like Shugart models...
Deunan wrote on 2021-05-16, 23:41:But here's the main problem - will the rest of the mobo be able to keep up. And I wouldn't bet on it I'm afraid... but you can try a lower overclock first, say install 38 or 40 MHz generator (the CPU clock is half of that).
Agree !!
Because the CPU crystal (32Mhz) is on the CPU card you might be able to find a diff back plane card to install, modding the one you have is "iffy" because the "chipset" is a bunch of TTL + PAL's which are most likely designed to run at speed based on the crystal. So changing the crystal to 66Mhz for a 33Mhz cpu will most likely fail. Just my opinion based on what little I can see from the pics.
What is the Zenith model number ? There should be some stickers on the back or inside the case.
Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun
I believe I have the service manual to that model, let me check my archive.
Deunan wrote on 2021-05-16, 23:41:You need the CPU swapped to something 33MHz rated to make sure it works at all, but then the actual frequency at which it'll run is decided by the mobo clock. Which sometimes can be replaced if it's a crystal generator in 4-pin metal package (and I would assume it is for this mobo). But here's the main problem - will the rest of the mobo be able to keep up. And I wouldn't bet on it I'm afraid... but you can try a lower overclock first, say install 38 or 40 MHz generator (the CPU clock is half of that). If you are lucky the original will be socketed, if not you have to desolder it and preferably put a socket there so you can swap and try easier. Do note, the final choice might need a zip tie to hold it in place, these things often like to work themselves out of the socket due to vibrations, that will prevent mobo from booting obviously and a few years from now it can happen to you - and you'll forget about the swapped generator and start poking everything else.
BTW that's a nice B1 stepping 386, too bad it's sigma-sigma. Still, plenty of interesting CPU bugs on it.
Thank You and I'm pretty sure it is socketed from the looks of it I can see the socket underneath the cpu and it is the one with the clay top which I believe is usually socketed from what I read I think. I did order a A80386DX-33 IV but still have to buy the 33Mhz 80387 Co Processor for it though.
vetz wrote on 2021-05-16, 23:50:I believe I have the service manual to that model, let me check my archive.
Yes Please Thank you! It has 4 bays on the front and one is 5.25 disk floppy drive and the other is a 3.5 floppy drive, though this one does not have a HDD hope to find a suitable one for it soon.
Zenith is very unfriendly computer to work with especially mods or overclocking. Leave it as is. Even the bios is odd too, nobody did it, just Zenith's homebrewed bios. The chipset is complex and over engineered, so many TTL chips and oodles of early PAL and GAL chips (programmable logic), LSI ICs to fail at higher speeds and hot running. Don't risk the computer dying from overclocking. 16MHz is very close for this large number of boards across slow bus. Even 20MHz might fail.
When I had IBM AT motherboard given to me, running at 8MHz, I tried 10MHz and it died shortly after, no chipset.
Get PSU's dust buildup blown out, don't let fan spin, also it's Zenith's home labeled components inside the PSU. Impossible to repair and very strangely designed. I even had a low-profile PSU computer by Zenith trying to fix PSU was impossible and smoked my MFM hard drive's motor as load (ST125) in big cloud of smoke even it was not spinning!
If PSU fails, the pinout is same number of voltages as AT (5V, 12V, -5V and -12V).
I was glad not to keep any Zenith computer. Zenith did produce of many types of computers, and strange engineering, on a cards, even on non-standard motherboard in a equally non-standard case, 8088, 8086, 286 and 386 types) back in the day, university had these in large number when they were new. Even the EazyPC was based on V40 SOC and is partially compatible and finding a mouse is a bugbear to get work and only works with 1 type of hard drive which were miniscribe 8 bit IDE, again unreliable.
Also reliability was poor. One computer needed socket repaired, I had many zenith boards that needed repaired, tracing the board to find failed chip is difficult.
Cheers,
Great Northern aka Canada.
thegenerallee86 wrote on 2021-05-16, 23:53:vetz wrote on 2021-05-16, 23:50:I believe I have the service manual to that model, let me check my archive.
Yes Please Thank you! It has 4 bays on the front and one is 5.25 disk floppy drive and the other is a 3.5 floppy drive, though this one does not have a HDD hope to find a suitable one for it soon.
Sorry, the one I have scanned is for the newer model which supported 20,25 and 33 mhz CPUs, else the case looks the same.
https://www.dropbox.com/s/l4kv059x6alwdmh/201 … 659788.pdf?dl=0
I might still have the manual for your model though, as the huge ring-binder the manual came in included other models as well.
vetz wrote on 2021-05-17, 01:00:I might still have the manual for your model though, as the huge ring-binder the manual came in included other models as well.
project UH19 is interested 😁
http://www.win3x.org/uh19/motherboard/result/ … ufacturerId=436
Horun wrote on 2021-05-16, 23:47:Agree !! Because the CPU crystal (32Mhz) is on the CPU card you might be able to find a diff back plane card to install, modding […]
Deunan wrote on 2021-05-16, 23:41:But here's the main problem - will the rest of the mobo be able to keep up. And I wouldn't bet on it I'm afraid... but you can try a lower overclock first, say install 38 or 40 MHz generator (the CPU clock is half of that).
Agree !!
Because the CPU crystal (32Mhz) is on the CPU card you might be able to find a diff back plane card to install, modding the one you have is "iffy" because the "chipset" is a bunch of TTL + PAL's which are most likely designed to run at speed based on the crystal. So changing the crystal to 66Mhz for a 33Mhz cpu will most likely fail. Just my opinion based on what little I can see from the pics.What is the Zenith model number ? There should be some stickers on the back or inside the case.
This is the Model # on the back of the computer case: ZBF-3339-EK
