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w2hx
August 28th, 2014, 05:03 PM
Hello folks,

I am the new owner of an IMSAI with the Cromemco Z80 ZPU board. I have yet to receive the system from the seller, so I am likely to have some troubleshooting ahead of me. However, I am interested in running a floppy/hard disk if possible. I have come across an drive system from an Xerox 820. The enclosure contains the power supply, one Shugart SA-850 floppy and one Shugart SA-1004 hard disk. The drive system, when connected to a Xerox 820 seems to work for both drives. There is a cable emanating from the enclosure with a 36-pin "D" connector.

Is there any reason why I should not be able to get this drive combination running with my IMSAI? I guess the main question is, what S100 board should I look for that would support these two drive types? And secondly, electrically speaking, is there any reason why this 36-pin connector might not contain all of the signals I would need to interface this with whatever s100 board I get?

I should also note, that this IMSAI also comes with a Cromemco 4FDC board, which I believe was designed for voice-coil drives, not the shugart. So I will likely not be able to use this board (except with the possibility of using it for other features it has such as serial port).

What advice can you give?
thanks

Eugene

Marty
August 30th, 2014, 06:25 AM
Hi All;
Eugene, You can the enclosure for Your power supply requirements for these two drives.. But, your Best bet, would be to get the ZFDC Board by John and Andrew, But You would need to Build the Board Yourself.. You can get the Board thru Gary Kaufman at http://n8vem-sbc.pbworks.com/w/page/...CB%20Inventory , Or You may/might still be able to get an Old Tarbell Floppy Disk controller on EBay, preferably their Double Density, but initially the Single Density Board is more readily available..
As far as the SA-1004, it is an SA 506 type of MFM drive and So You would need to find an S-100 controller for it, I don't know if John and/or Andrew have an S-100 MFM Controller.. Mine came from MiniScribe..

THANK YOU Marty

JDallas
August 30th, 2014, 08:06 AM
...I am the new owner of an IMSAI with the Cromemco Z80 ZPU board...
I have the original complete set of documentation for my Cromemco ZPU board. If you have questions on that I should be able to help.


...I am interested in running a floppy/hard disk if possible...
The hard drive will be the bigger challenge. I'd recommend you get the floppy going first and then all Cromemco system issues resolved before then considering the hard drive interface.

Be sure to read up on vintage computer restoration regarding the capacitors that dry out. Particularly on the huge linear power supply in the back of the case... generally you replace those caps before even trying to power up.

When you do power up first, make sure you have ALL the S-100 cards removed from the bus first. Instead of completely removing the cards I normally just assure power is off and then pull them out of the connector about 2 or 3 inches, still supported by the card slots, *BUT* if I were powering that huge Cromemco power suply with possible capacitor flame outs, I'd remove them COMPLETELY. If the power supply smokes or pops, just immediately turn off the switch on a power-bus its connected to.

Before removing cards from the lateral S-100 card cage, be sure to document their position and orientation (i.e. component side). The positions are less critical but sometimes cables don't reach if you change it up much.

Once you have stable power voltage levels, you can than consider what boards you want to try (never install or remove cards while power is ON; always power off first).

There may be issues with some of the capacitors on the boards too, but pick a minimum set you need to get a basic toehold to computing and search online for any documentation from someone that has done the same boards first.


...I have come across an drive system from an Xerox 820. The enclosure contains the power supply, one Shugart SA-850 floppy and one Shugart SA-1004 hard disk....
I had a Xerox 820 in the old days. I'd recommend disconnecting the hard drive disk cables until later when more is running well. The 8 inch drive should be compatible (maybe someone will inject better information) as the interface is the same for all the standard drives... just some timing and pin assignment use. Most can be handled by changing the jumpers on the drive (aka FDD for flopy disk drive).

Your Cromemco floppy disk controller (FDC) card should do fine after some possible capacitor replacements (an easy job, just annoying waiting for parts to arrive). People here can help you solder with the right equipment. Note though that the FDC probably won't support "double density" floppy formats, but once you get everything working, you can then consider upgrading that as someone suggested, or focus your spare time and money on the hard drive instead. Generally speaking, don't buy things that require that computer to function UNTIL you know it will function.


...There is a cable...from the enclosure with a 36-pin "D" connector...
Usually there is a 50 pin connector for 8 inch drives and 34 pin connector for 5 1/4 inch drives that came along later than the Cromemco. You many find documentation PDF files on that board. I usually go to the following website for old documentation first:

http://maben.homeip.net/static/S100/cromemco/index.html

If you go one directory up from that Cromemco page, you'll find a lot of other brands.


...electrically speaking, is there any reason why this 36-pin connector might not contain all of the signals I would need to interface this with whatever s100 board I get?...
If that is the Cromemco floppy disk controller, it will likely do everything you need, but maybe not everything you want. For example its unlikely to support double density floppies, but you can add that later.

When connecting a floppy drive, documentation for the drive and controller board helps a lot. What you basically do is select the drive number and jumper out some features you don't need. You can add some back later. This forum (VCF) has an online chat channel which can be a good source for quick help.

server irc.slashnet.org 6667
server slashnet.org 6667

I found it useful putting my Cromemco Z-2 System together back in 1978 to tabulate the S-100 pin assignments and polarity on all boards before plugging them in. If all boards are made by the same company, that's not likely to be necessary. Memory cards are usually simple and don't use any divergent S-100 pins.

I've found some of the poorly defined and seldom used S-100 pins used for different things which forced me to modify those boards to another unused pin. One board even had one pin with the wrong polarity... so I had to jumper in an unused inverter gate on that board to be compatible. The S-100 wasn't standardized until the early 80s as the IEEE-696.



...a Cromemco 4FDC board, which I believe was designed for voice-coil drives...
Probably won't make any difference. Later you may want to get a FDD upgrade to get better performance and double sided floppy support (assuming the drive doesn't have that).

w2hx
August 31st, 2014, 10:30 AM
Thanks everyone!

w2hx
September 1st, 2014, 11:45 AM
Thanks very much, JDALLAS for the offers of help. will contact you if needed (very likely)!

JDallas
September 1st, 2014, 03:31 PM
No problem. I'm often in vcf's IRC chat as " jd ". I monitor it on a netbook until lunch and then again in the evening.

MikeS
September 1st, 2014, 04:01 PM
No problem. I'm often in vcf's IRC chat as " jd ". I monitor it on a netbook until lunch and then again in the evening.What are folks using for an IRC client (WinXP)?

JDallas
September 1st, 2014, 05:18 PM
What are folks using for an IRC client (WinXP)?
If you use FireFox, the Chatzilla plug-in for FireFox is simple enough. Not near as powerful as Mirc but who needs all the bloat?