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Teufelhunden
March 31st, 2015, 07:54 AM
What do you guys think of this auction? I'm considering grabbing it:

http://www.ebay.com/itm/111634068504?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

I'm assuming the worst as far as working, but the price looks low compared to others I was watching a few months ago.

taborj
March 31st, 2015, 08:59 AM
If you've got the cash, and are looking for that particular model, I don't see any big red flags. I'm by no means an IMSAI expert, though. Heck, the auction lists a 30-day return policy, so you could always return it if it's not as represented! :) The seller has a high rating with a lot of auctions to their credit, so that's a plus.

smp
March 31st, 2015, 09:14 AM
From the pictures, it appears to have an 8080 processor board, a few memory cards, a bunch of I/O boards (that may or may not be useful to you), and also has some modifications made to the power supply. They do not talk about providing any documentation, and they show the obligatory picture with the power turned on, where you see all address lines except A2 and all data lines lit up. So, the LEDs work, but there is no indication that anything else is actually working.

I think that $2100 (BIN plus shipping) is a bit steep for this one. I have purchased similar machines in the past for $1000-$1500, but that was in the past.

I would be more sympathetic if this was an individual Seller who you could get into a conversation with and find out what he knows and what he has actually done with the machine. I would be more inclined to try and contact this institutional Seller and see if they might be open to take an offer of something like $1000 or $1500, or re-list it with a more reasonable BIN, but that's me.

My IMSAI has a Z-80 CPU board, a 64K RAM board with one of the RAMs in high memory replaced with an EPROM with a system monitor installed, and a S100computers.com SIO board, and it is working. Using the system monitor with a laptop connected to the SIO for a terminal, you can load HEX files to get programs into the machine. The blemishes are that 3 or 4 switch paddles are missing (I have spares but have not had the guts to try and install them), and it has a clear plexiglass cover rather than the blue metal original cover. If I were to list my machine, I would like to list it for $2500, but I do not know if I would actually get it.

Good luck!

smp

dfnr2
March 31st, 2015, 09:39 AM
The price does not seem low to me, but also not outrageous. Given that it comes with a decent complement of memory, etc., and that the front panel at least lights up, I'd say there's a good chance it works or can be made to work. There's nothing unique about this unit that would make it risky to pass up.

I would expect it to sell for somewhere in the $1500-$2000 range on auction, so it's at the upper end of what I would expect for this unit. I'm sure a similar one will come along and sell for less, if you're not in too much of a hurry.

It does look like a nice unit though.

Teufelhunden
March 31st, 2015, 09:43 AM
Thanks for the advice guys! I think I will hold off for now and see if it gets relisted at a lower price.

leiy
March 31st, 2015, 09:00 PM
Definitely a nice computer, C8080A date code 7604 tells its age.

NeXT
April 1st, 2015, 02:24 AM
Two grand? Forget it.

g4ugm
April 1st, 2015, 09:38 AM
It looks an early(ish) serial number. They started at 1000 and the label on that is 1990 so in the first thousand made. How many of these did they make.

g4ugm
April 1st, 2015, 09:48 AM
Checking the "sold" listings this rather newer model:-

http://www.ebay.com/itm/191537608541

went for a wopping (and it says sold) US $2,669.99...

the last one at auction, which was really scruffy

http://www.ebay.com/itm/301544773064

went for US $1,525.00 and that had only one card in it. So I would ay for what you are getting its a "fairish" price. I would expect it to sell...

leiy
April 1st, 2015, 05:39 PM
Checking the "sold" listings this rather newer model:-

http://www.ebay.com/itm/191537608541

went for a wopping (and it says sold) US $2,669.99...

the last one at auction, which was really scruffy

http://www.ebay.com/itm/301544773064

went for US $1,525.00 and that had only one card in it. So I would ay for what you are getting its a "fairish" price. I would expect it to sell...

I feel the price of the IMSAI 8080 is neutral. It has full fledged configuration and complete port on back.

I have couple of S-100 computers in collection, so I will not buy it this time.

BubbaShakers
April 8th, 2015, 10:30 AM
New member here. I "cut my teeth" on Apple II's (//c, //e, and later IIgs) in high school, and am an inveterate collector of "old stuff" (e.g. 1920's era radios). I've always wanted an IMSAI since seeing ads for them in old computer magazines when I was in college. I am the one who purchased the system in this thread.


My initial goal is to get this system working to the point to where I can key in a simple program via the front panel and have it execute (e.g. the test program described in the IMSAI assembly manual). I used to build my own boxes for running OS/2 in the early '90s and know my way around 80's and 90's Intel and Apple equipment fairly well, but this is my first S-100 box.


The system as I received it contains the following:


IMS MPU 4 Rev A
MITS 88-16MCS 16K Static RAM (configured for 0-3FFF)
California Computer Systems - 2016B 16K RAM Board (configured for 4000-7FFF)
(2) Solid State Music 4K Static Ram Cards (configured for C000-CFFF, D000-DFFF)
IMSAI - RAM 4A Card (configured for F000-FFFF)
IMSAI SIO Rev 3 (Connected to 2 DB25 ports on the rear panel marked 44H & 45H Serial and 42H & 43H Serial)
Northstar MDS Disk Controller (no cabling / connections present)
Cromemco D+7A I/O (Connected to a number of individual I/O jacks on top of the back panel, and a couple of DB25 ports marked 18H parallel in and 18H parallel out)
Bus Extender


I'm guessing there was once another 16K RAM card for 8000-8FFF as well as another 4K RAM card for E000 that are no longer present (or are there other reasons why the system would be deliberately set up with these gaps?). In addition there are ports on the back (marked Lear Seigler and Sperry -- I'm guessing the former at least was for a terminal) that are connected to a couple of loose edge connecters -- presumably there was at least 1 other i/o board present that has since been removed.


I have downloaded all the 8080 manuals from imsai.net, and found manuals for most of the 3rd party cards on s100computers.com.




I have NOT attempted to power the system on since receiving it, and would appreciate pointers on how to proceed. I have a basic multimeter but no oscilloscope. Based on smp's comments above I'm not assuming that anything works.


My initial thinking is start by pulling all the cards and testing the voltages on the power supply first (I just had to recap the power supply in an Apple IIe that gave up its magic smoke after powering it on for the first time in 15 years - would rather avoid that here). The IMSAI manual describes testing the power supply -- but with the front panel card in place. Is this safe, given the age of the electronics? If not, can an "empty" system with just the backplane (appears to be a fully populated EXP22) be safely powered on and used to get reliable voltage readings?


Thanks,
Jason

BubbaShakers
April 13th, 2015, 06:06 AM
So I ended up pulling the cards (except for the CP-A), testing voltages, and adding just the MPU and 1st RAM card back, testing, then re-adding the remaining cards one at a time - each time reentering the small test program from the assembly guide. After the cards were all added back I entered and ran a few other programs I found on on the net, including the "cylon effect" program for the programmed output lights I found on Lawrence Woodman's site.

To net things out, the system seems to be working (at least the CPU and RAM -- haven't tried to do anything with the IO boards other than verify the system continues to behave with them in place).

I am having an issue though, with the deposit next switch not working -- but only on one of the RAM cards.

For some reason, deposit next is unreliable with the first memory card. It will always advance the address, but will usually not write to memory (it seems to always store if all 0s, but but for nonzero bit patterns it will usually store only a subset of the 1's). The deposit ("up position") switch always works, and I can enter programs by using deposit next to advance the address, then flipping the switch up to actually store. At first I thought there was an issue with the switch itself, or with the circuitry on the CPA, except that deposit next works flawlessly on the other 4 memory boards.

The problematic card is an MITS 16K at address 0000. The other cards consist of a CCS 16K, a couple of Music 4K cards, and an IMSAI RAM4A. All are static memory cards. I can deposit/deposit next and examine/examine next memory on the other cards without issue (some of them even have LEDs that light up when the memory on the card is accessed).

There's not much in the way of configuration on the MITS card -- just a single dip switch bank used to set the base address.

leiy
April 13th, 2015, 06:54 AM
So I ended up pulling the cards (except for the CP-A), testing voltages, and adding just the MPU and 1st RAM card back, testing, then re-adding the remaining cards one at a time - each time reentering the small test program from the assembly guide. After the cards were all added back I entered and ran a few other programs I found on on the net, including the "cylon effect" program for the programmed output lights I found on Lawrence Woodman's site.

To net things out, the system seems to be working (at least the CPU and RAM -- haven't tried to do anything with the IO boards other than verify the system continues to behave with them in place).

I am having an issue though, with the deposit next switch not working -- but only on one of the RAM cards.

For some reason, deposit next is unreliable with the first memory card. It will always advance the address, but will usually not write to memory (it seems to always store if all 0s, but but for nonzero bit patterns it will usually store only a subset of the 1's). The deposit ("up position") switch always works, and I can enter programs by using deposit next to advance the address, then flipping the switch up to actually store. At first I thought there was an issue with the switch itself, or with the circuitry on the CPA, except that deposit next works flawlessly on the other 4 memory boards.

The problematic card is an MITS 16K at address 0000. The other cards consist of a CCS 16K, a couple of Music 4K cards, and an IMSAI RAM4A. All are static memory cards. I can deposit/deposit next and examine/examine next memory on the other cards without issue (some of them even have LEDs that light up when the memory on the card is accessed).

There's not much in the way of configuration on the MITS card -- just a single dip switch bank used to set the base address.

The benefit of MITS 16K SRAM board is very low heat dissipation compared to other same era 16K SRAM card, you can try to change faulty chips on the MITS SRAM board.

Marty
April 13th, 2015, 07:11 AM
Hi All;
Bubba, One thing to be aware of is that You have an Imsai and You are using a Mits Board in it, So, Mits has pins 20 and 70 for Protect and Unprotect.. If I remember correctly, Imsai Grounded one of those and did something else to the other pin with a diode..
So, the Mits board might be in Protect mode..
To check for sure put some scotch tape over pins 20 and 70 and Retest the Board, and see if You can Write to it..

THANK YOU Marty

leiy
April 13th, 2015, 07:15 AM
Hi All;
Bubba, One thing to be aware of is that You have an Imsai and You are using a Mits Board in it, So, Mits has pins 20 and 70 for Protect and Unprotect.. If I remember correctly, Imsai Grounded one of those and did something else to the other pin with a diode..
So, the Mits board might be in Protect mode..
To check for sure put some scotch tape over pins 20 and 70 and Retest the Board, and see if You can Write to it..

THANK YOU Marty

Hi, I have MITS 16K SRAM board on Altair 8800, but there has no protection mode on these card maybe.

Marty
April 13th, 2015, 07:29 AM
Hi All;
Leiy, If you are using a Mits memory board in a Mits machine, then You have a Protect and Unprotect Switch on the Front Panel.. Which Sets or Unsets the the protect Flip-flop on the Memory Board..

THANK YOU Marty

leiy
April 13th, 2015, 07:44 AM
Hi All;
Leiy, If you are using a Mits memory board in a Mits machine, then You have a Protect and Unprotect Switch on the Front Panel.. Which Sets or Unsets the the protect Flip-flop on the Memory Board..

THANK YOU Marty

Hi, Marty, I can't toggle on protect mode on MITS 16K SRAM, but I can toggle to activate protect on MITS 1KB SRAM board.

Marty
April 13th, 2015, 08:06 AM
Hi All;
Leiy, Without a schematic, to look at, I can't say if the protect mode is there or nor on the 16K SRAM..
But, one way to find out is to see If there are any connections to pins 20 and 70 on the bottom of the Board..
If there is a connection, then it might need further looking into, otherwise if there is no connection, then there is no Protect/Non-protect..
THANK YOU Marty

BubbaShakers
April 13th, 2015, 09:44 AM
The manual for this card does not mention a write protect feature, nor does the schematic show pins 20 or 70 active. In any event, if this was a write protect issue, why would deposit work but deposit next fail (wouldn't they both fail)?

On a side note, I noticed the front panel did not work at all when I initially put the D+7A IO card back in. I found a note on Herb Johnson's site about pins 70 and 20 causing issues on front panel systems with other Cromemco cards, and sure enough a bit of scotch tape over those 2 pins allowed the front panel to start working again with this card inserted. The deposit next issue occurs, however, even if the MPU and the RAM cards are the only cards in the system.

leiy
April 13th, 2015, 07:14 PM
Hi All;
Leiy, Without a schematic, to look at, I can't say if the protect mode is there or nor on the 16K SRAM..
But, one way to find out is to see If there are any connections to pins 20 and 70 on the bottom of the Board..
If there is a connection, then it might need further looking into, otherwise if there is no connection, then there is no Protect/Non-protect..
THANK YOU Marty

Thanks for valuable advice.

BubbaShakers
April 14th, 2015, 05:41 AM
Looking at the schematic for this board (and confirmed visually by looking at the card itself), pins 20 and 70 do not appear to be active. In any event, if this were a write protect issue, why would deposit work but deposit next fail? Remember, I keyed in and ran several programs from the card (the "cylon effect" program I let run for 20 minutes or so) -- I just have to use deposit -- but only on this card (deposit next works on the other cards).

-Jason

Marty
April 14th, 2015, 12:33 PM
Hi All;
Bubba, Yea, but that at least eliminates, any possibility of that being the problem..
My next suggestion, is that, either the 74123 that makes the pulse for the deposit next, either is Bad itself, or the Cap or Resistor attached to it are bad or out of tolerance.. The timing for both the Deposit and the Deposit Next should be the same length..
Try swapping the 74123 that is used for the Deposit Next with one of the other 74123's.. In fact all of the 74123's for the read/write chain should be checked, Examine and Examine Next as well.. A scope would be even better, but, I think you said a scope you didn't have..

THANK YOU Marty

BubbaShakers
April 27th, 2015, 01:09 PM
So I finally got around to removing the front panel and tried shuffling the 74123's around with no change in results. The resistors appear to be in spec, but I'm not aware of any way to test the caps without breaking out the soldering iron, which I'd rather not do at this point for such a relatively minor issue (which may or may not be with the card itself). I have also acquired an additional RAM card (an IMS 16K 282 SRAM). This new card, in addition to the other 4 SRAM cards that originally came with the system, seems to work fine with deposit next (as well as deposit, examine/next).

I ended up just reconfiguring the MITS card to fill 8000-BFFF and configuring the IMS card for 0-3FFF, since almost all program entry via the front panel will be done in that range. The system still has a 4K "hole" at E000, and from my research the (not currently used) Northstar FDC has ROM mapped within range at E800.

It also occurred to me that none of the programs I've been toggling in and playing with actually try to write anything to memory. With that in mind I decided to try and write a quick and dirty "memory exerciser" that was small enough to key in via the front panel. This is my first attempt at 8080 assembly programming (haven't done any assembly since IBM 370 course in college), so there are almost certainly bugs. In any event it seems to run on my system (I can see it hitting the various cards that have activity LED's as I select ranges with the switches), and did not detect any errors.

I also have an even simpler (26 byte) program that just blasts a range of memory with a test pattern, which you can then "spot check" with examine/next. I can post this as well if interested. Following the asm source is a "nibbleized" listing to better facilitate front panel entry.



title 'imsai trivial memory exerciser'
; Jason R. Kersten
;
; Quick and dirty memory tester, small enough to enter via front panel
; Programmed Input Switches 4-7 select 4K address block to test
; Loops endlessly in chosen block writing 4K block with test pattern
; (alternating 1s and 0s) then reading and testing. The test pattern is rotated for each
; byte written.
;
; Programmed Outpt LED's show status:
; *......* = Waiting for address selection (PI switches all down)
; *....... = Writing test pattern to memory
; .*...... = Reading/Testing
; ....**** = Error detected
;
; If an error occurs (pattern read in doesn't match written), program will
; show error status and loop. Stop the program via front panel and examine 0x004F (lo)
; and 0x0050 (hi) to see address where failure detected.
;
; Caveats:
; * Does not test 0-0FFF (at least the first 80 bytes of which had better be good ;)
; * Not a "real" test -- will not catch certain errors. Mainly meant as a "sanity
; test" to verify a memory card is recognized by the system (in it's entirety) and
; mapped correctly to where it's supposed to be (and as an exercise to get my head
; wrapped around 8080 assembly).
;
; Status outputs (these are all complements of what actually appears on the LEDs).
sfill equ 01111111b
stest equ 10111111b
sfail equ 11110000b
swait equ 01111110b
panel equ 0ffh
pat equ 01010101b
org 0h
mvi a,swait
out panel
mvi e,pat
;Get starting address from programmed input.
loop: in panel
;if all switches are down (0-0FFFh selected)
;sit in tight loop to avoid overwriting ourselves
cpi 0
jz 0
ani 0f0h
mov h,a
mvi l,0h
shld start
mvi a,sfill
out panel
;Fill 4K Memory block starting at base with test pattern
lxi b,1000h
fill: mov m,e
mov a,e
rlc
mov e,a
inx h
dcx b
mov a,b
ora c
jnz fill
;Test the 4K Memory block we just filled
mvi a,stest
out panel
lhld start
lxi b,1000h
test mov a,e
mov d,m
cmp d
jnz err
rlc
mov e,a
inx h
dcx b
mov a,b
ora c
jnz test
jmp loop
;Error encountered. display error on programmed output and store bad adress
;Beware missing address ranges and ROM.
err: mvi a,sfail
out panel
shld baddr
;Chase our tail until the user stops via the front panel.
tail: jmp tail
start dw 1000h
baddr dw 0000h
end






Nibbleized listing for front panel entry:


PROGRAM: memtest
ADDR DATA
8421|8421
---------------
0000: 0011 1110
0001: 0111 1110
0002: 1101 0011
0003: 1111 1111
0004: 0001 1110
0005: 0101 0101 ;Test pattern (rotated left carry for each byte written)
0006: 1101 1011
0007: 1111 1111
0008: 1111 1110
0009: 0000 0000
000a: 1100 1010
000b: 0000 0000
000c: 0000 0000
000d: 1110 0110
000e: 1111 0000
000f: 0110 0111
0010: 0010 1110
0011: 0000 0000
0012: 0010 0010
0013: 0100 1101
0014: 0000 0000
0015: 0011 1110
0016: 0111 1111
0017: 1101 0011
0018: 1111 1111
0019: 0000 0001
001a: 0000 0000
001b: 0001 0000
001c: 0111 0011
001d: 0111 1011
001e: 0000 0111
001f: 0101 1111
0020: 0010 0011
0021: 0000 1011
0022: 0111 1000
0023: 1011 0001
0024: 1100 0010
0025: 0001 1100
0026: 0000 0000
0027: 0011 1110
0028: 1011 1111
0029: 1101 0011
002a: 1111 1111
002b: 0010 1010
002c: 0100 1101
002d: 0000 0000
002e: 0000 0001
002f: 0000 0000
0030: 0001 0000
0031: 0111 1011
0032: 0101 0110
0033: 1011 1010
0034: 1100 0010
0035: 0100 0011
0036: 0000 0000
0037: 0000 0111
0038: 0101 1111
0039: 0010 0011
003a: 0000 1011
003b: 0111 1000
003c: 1011 0001
003d: 1100 0010
003e: 0011 0001
003f: 0000 0000
0040: 1100 0011
0041: 0000 0110
0042: 0000 0000
0043: 0011 1110
0044: 1111 0000
0045: 1101 0011
0046: 1111 1111
0047: 0010 0010
0048: 0100 1111
0049: 0000 0000
004a: 1100 0011
004b: 0100 1010
004c: 0000 0000
004d: 0000 0000
004e: 0001 0000
004f: 0000 0000 ;lo byte of bad address
0050: 0000 0000 ;hi byte of bad address