Kaypro 10s - Won't start without HDD connected?

[k0d3g3ar]

Thought I would ask the community about this. I have 3 x K10s of different configurations, etc. and as to be expected not one HDD works. Consequently they are pretty much useless. So I started down the FreHD route and I'm trying to get that going on one of them, but in all 3 cases I found something really interesting and wanted to know if anyone has a solution.

If I remove the HDD (by way of the controller cable that comes from the mobo), but leave the FDD attached, and I try to turn it on, it won't even power up. I managed to get the rear fan to operate, but it seems that the PSU doesn't want to give power to the mobo if the HDD is not connected. Or at least it maybe that the power is going to the mobo but the K10 refuses to start at all without the HDD connected.

Have others that have opened up these bad boys found something similar? Is there any easy tweak that I need to do that I am overlooking?

Thanks in advance for any ideas.

Myles

 

[durgadas311]

It might help to know what ROM version(s) you have, and possibly mainboard part numbers. The "universal ROM" (81-478) should operate without any HDD controller, since it is designed to operate in all configurations. It's possible that the older K10 ROM might have a dependency on talking to the controller.

Can you tell how far it gets? Does the CPU run but just nothing appears on the screen?

You might try leaving the controller connected but disconnect the HDD from the controller. The ROM should give preference to booting off the floppy, I think.

 

[k0d3g3ar]

It might help to know what ROM version(s) you have, and possibly mainboard part numbers. The "universal ROM" (81-478) should operate without any HDD controller, since it is designed to operate in all configurations. It's possible that the older K10 ROM might have a dependency on talking to the controller.

Can you tell how far it gets? Does the CPU run but just nothing appears on the screen?

You might try leaving the controller connected but disconnect the HDD from the controller. The ROM should give preference to booting off the floppy, I think.

I have attached photos of each mobo I have. It looks like none of them have the Universal ROM you are referring to. Would that be the issue?

It doesn't get far at all. No visible sign of anything to be honest. Not even power appearing to get to the CRT or image, no activity showing on the FDD, nothing.

 

[maxtherabbit]

I don't own a kaypro, but that sure sounds like a minimum load issue. The HDD probably represents the only meaningful load on the 12V rail, without which the SMPS will just not start up.

 

[durgadas311]

Very interesting. You have two different mainboards there. The first phot os of some weird 2X/K10 hybrid board that I don't find anywhere in the technical manual. It's main layout is that of a 2X (and later) board, but the back panel connectors are laid out like a K10. The other two look like traditional K10. The second board shows that the ROM socket is empty, so that won't work as shown. The third board shows the CPU socket is empty, so won't work either. The third does show ROM 81-302, which is normal for that model.

The first also shows ROM 81-302, which seems out of place to me at first. That board has the modem and RTC (and PIO) un-populated, but appears to have the HDD interface populated (the 2X was shipped with all that un-populated). Otherwise, I think the hardware on this board is software-compatible with the K10 board, so maybe the 81-302 ROM will work OK there.

The last two boards both show the HDD controller disconnected - which I assume you did for visibility. Did you try with the HDD controller connected (and powered up)? Possibly with the HDDs also connected and powered (in spite of their failed status). Do you have a floppy you can try to boot?

I'm pretty sure the power supply is just a conventional linear supply, and so the 12V still "start up" regardless. 12V is still used for RS-232, floppy drives, and probably some other things as well.

 

[k0d3g3ar]

I don't own a kaypro, but that sure sounds like a minimum load issue. The HDD probably represents the only meaningful load on the 12V rail, without which the SMPS will just not start up.

That sounds entirely reasonable. It definitely appears like no power is getting to the mobo, although I haven't put a meter on it to test that. I can try and artificially generate the load there and see if I get different results.

Myles

 

[k0d3g3ar]

There was a daughter board that looks like it was a 3rd party board connected to one of the mobos. I removed it, to gain access to the connector to the HDD controller, but I can put it back. It connected over a chip on the board, that was then moved into the daughter board. I'll check the vendor on it - it is something I didn't recognize and definitely looks like the original owner must have added as an after market thing.

So if I understand it, of the three photos, if you were going to put some time into trying to make one work, which would you choose as your primary candidate?

 

[durgadas311]

There were some add-ons that sat on top of the CPU socket and interfaced there to add new hardware. I'm guessing that was the daughter board you removed. I assume the 40-pin chip was the CPU, but you do want to make sure it is a Z80. Mostek made 2nd-sorce Z80s that had different part numbers and weren't so obviously a Z80-CPU. I think they were MK3880. Those are drop-in replacements for Z80-CPU. But it is conceivable that it was something else entirely, so you need to check.

It's hard to say which board is the best bet. The "2X" style board is newer, but it all depends on it's condition. You've got lots of spare parts to swap around to try and get one working. The 1793 FDC is probably the most valuable, as you can't really get those anymore. Maybe since the "2X" board is complete (or looks to be) that might be the place to start. The one that's missing the ROM certainly won't function until that is replaced.