Imsai VDP 80 Thoughts

[applequack]

I have the opportunity to buy a pretty rare system, but it's also in terrible condition. My understanding is that these units weren't well designed, and had thermal issues that plagued the floppy drive, particularly, and made it require constant realignment.

Being an S-100 fan, I already have several Imsai 8080s, but I've only seen this unit online, never in person. The CRT is toast. There is some leakage that has affected the motherboard. It may be impossible or unfeasible to resurrect.

I still am thinking of buying it. If anyone has any recent data on pricing, and what a reasonable offer might ballpark out at, I would greatly appreciate it. I'm thinking perhaps $500, and if I can't ever get it going, it's still a cool-looking piece of early computer history.

 

[ajacocks]

That is a really cool machine, and I have not heard of it, before. I'd be quite tempted, in your place.

- Alex

 

[pbirkel@gmail.com]

Looks like the CRT simply has cataracts, which can be corrected. Hopefully those aren't hiding burn-in. A side-effect of the cataracts is that because the PCB is located directly under the face it was the recipient of the leakage. Can't tell from the photo just how bad the consequences might be.

 

[snuci]

I have one. I don't remember if the drive is a Persci 277 or 299 but it will require some maintenance. My own VDP-80 is not running but I have not attempted a restoration yet. If the drive is a Persci 277, there is a guide by Martin Eberhard that can help you restore it. I used it for the Helios II drive in the SOL-20. From the cataract damage and "leakage", I don't think there is anything directly under it but it's been a while since I had mine opened. I think it's the heaviest computer I have. They are extremely heavy. As for price, it's really hard to determine. It is very rare but there is damage so it really is between you and the seller what you are willing to offer and what they are willing to accept.

Here is a picture of what's under the monitor. It may just be corrosion on the monitor frame.



Good luck.

 

[applequack]

Looks like the CRT simply has cataracts, which can be corrected. Hopefully those aren't hiding burn-in. A side-effect of the cataracts is that because the PCB is located directly under the face it was the recipient of the leakage. Can't tell from the photo just how bad the consequences might be.

Hmm, that makes sense. I did a little reading about this. And yes, the PVC safety coating has melted down onto the PCB, which is no fun.

 

[pbirkel@gmail.com]

Hmm, that makes sense. I did a little reading about this. And yes, the PVC safety coating has melted down onto the PCB, which is no fun.

Well, yuck. My experience was with repairing an HP 2645A terminal that looked just about like your CRT; ugly. There are various approaches to lifting off the safety glass; I successfully used a flexible knife to gradually detach the periphery and then the center area was liquid enough to simply lift off the entire sheet (with some suction). See the attached pictures. The residual gunk cleaned up with mineral spirits. Fortunately only the case was damaged in consequence of the leak. I used silicone double-sided tape to reattach the face plate at the periphery. My backup plan was the hot-wire technique. I've read about the solvent-soak as well, but didn't get to that stage :->.

As @snuci pointed out, that's a PerSci dual-drive there (and, yes, it's HEAVY). It's a fast voice-coil mechanism that performs similar to a HDD of that era. But very finicky. That oxidation seen on the interior pan in the third photo doesn't bode well for getting that PerSci FDD to work again. I'd think in terms of having to replace it. Probably there's enough room to hide a Gotek emulator somewhere (behind the fan?) and then use an extender cable to bring out the card-slot to a location on the back panel (perhaps an empty DB25 cutout), leaving the PerSci to look good, but I expect that you'd need to swap the existing FDD controller (only a very few worked with the PerSci) for a more conventional one. Or you could just attach an external FDD subsystem. So I'd take that all into account when haggling.

There's a 7-slot card cage; what's populated there? According to sales literature there should be a DIO-C controller. If that's missing then you have another challange to obtain a suitable FDD controller in order to try to restore the PerSci drive. There should also be a VIO board for the display. And a CPU board ... and a memory board ("32K/64K") ...

Is there any media or technical documentation? It looks like the Maslin C-D archive includes some VDP-80 8" software in the dddrive/Sydex/8in folder.

IMO $500 is a reasonable offer-point. Expect to do a fair amount of restoration work.

 

[pbirkel@gmail.com]

PS: My comment WRT $500 as an offer point was based on the assumption that the card cage was appropriately populated with undamaged cards. If it's empty then a lot depends on your "appetite" for a major restoration :->. As you've already got several IMSAI 8080's "under your belt" presumably you already know the drill ...

 

[seaken]

Well, I don't know much about that machine but I was thinking it looks really cool! I would be happy just to have it cleaned up and on display. If I were talented enough to get it working that would be just an extra goodie.

I once owned a NorthStar Horizon with a Televideo terminal. I wish I still had it and regret giving it up. (But I didn't know I would end up an old computer enthusiast back then). This IMSAI is way nicer to look at. I am working on restoring my NorthStar Advantage now and things are looking good. But again, this is way cooler! I hope you can get it.

Seaken