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Godbout Interfacer 1 stops Imsai´s front panel...

J

Jan1980

Experienced Member
Joined
Mar 13, 2015
Messages
72
Location
Germany
Hello.

I own godbout interfacer 1 serial card. When i mount it to my imsai 8080 motherboard, i cannot examine or deposit anymore. Imsai seems to be blocked out. Now, with my logic probe, i checked the 74xx logic chips, they seem to be fine. Which signal on S100 can stop the system ? First, i thought, one of the databus driver is damaged, but they look fine on logic probe. Do you have an idea ?

thx

Jan
 
The IMSAI front panel has incompatible signals with IEEE S-100 compatible cards.
Many cards have ways to disable the offending signals, you'll have to check the Interfacer 1 manual to
see if they can be disabled.
 
Jan1980 said:
Hello.

I own godbout interfacer 1 serial card. When i mount it to my imsai 8080 motherboard, i cannot examine or deposit anymore. Imsai seems to be blocked out. Now, with my logic probe, i checked the 74xx logic chips, they seem to be fine. Which signal on S100 can stop the system ? First, i thought, one of the databus driver is damaged, but they look fine on logic probe. Do you have an idea ?

thx

Jan
Click to expand...

I believe you had DRAM. What kind of DRAM board do you have. Many don't do real refresh, controlled by the CPU. Things like interrupts from the serial card can cause the DRAM to stop refreshing. You can put clear tape on pins to mask them. I put it so the tape is on the fiberglass edge of the board's connector, so that the clean edge is at the edge of the connector, and then use razor to trim it to the width of the pin to remove the excess. I then plug it into the mother board. This allows you to easily isolate a pin you think may be an issue. You can remove the tape easily later. Just don't leave it on the pin for 5 years.
Dwight
 
Looking at the interfacer 1 manual, I don't see anything that should be an issue. The only driven signals onto the bus are the data lines and the interrupts.
Dwight
 
The CompuPro Interfacer 1 as well as most other CompuPro boards were designed to meet the IEEE696/S100 standard. This causes a problem when these boards are used in an IMSAI as Al Kossow pointed out above. CompuPro described the issue (and the solution) as follows:

"The new IEEE 696/S-l00 bus standard calls for lines 20 and 70 to be grounded on the bus. When the IMSAI front panel was designed, many memory boards had the capability to be "protected" from accidental writes to the board. To accommodate these boards, the IMSAI front panel grounded line 70 but pulled up line 20 with a resistor that also enabled all the front panel functions. When DISK 1 [or any other IEEE696 standard S100 board] is inserted, line 20 is grounded and the front panel is disabled. The solution is to cut line 20 on the front panel since this line is now defined as ground."

Alternatively, if you prefer not to modify the IMSAI and you don't plan to install any other IEEE696/S100 boards into it, you could cut the trace leading to line 20 on the Interfacer 1.
 
Al Kossow said:
Did you check the extra ground pins?
Click to expand...

I didn't think of that, thanks for reminding me. More tape to mask pins. I would think the thin packaging tape would work well. You want it to be thin so as to not bend the socket pins.
70 and 98 might be the only issues. Look at the charts Retrotechnology.com has.
Dwight
 
Last edited:
Hello.

I tried the card without bus drivers. Then, i decided me to cut the pin 20 on the interfacer. Then, i removed bus drivers again. Always the same, frontpanel not working. Only RUN/STOP and RESET. I am using 2 Salota mixed memory cards with static RAMs. Every card has 32kb. On the card in the higher memory space are installed 2 empty 2716 eprom. One located on F000, the other located on F800. Later, i´ll use the F000 for floppy bios and the one on F800 for a small machine language monitor.
I´ve also other memory cards in stock with dynamic RAM. Always the same. Which lines can also cut off the front panel ??

thx

Jan
 
I have forget to say. Pin 20 is cutted together with Pin 70. No, i disconnected (with thin tape) Pin 98, then 99. Always the same.. FPA not working...

thx

Jan
 
Jan1980 said:
I have forget to say. Pin 20 is cutted together with Pin 70. No, i disconnected (with thin tape) Pin 98, then 99. Always the same.. FPA not working...

thx

Jan
Click to expand...

You really should use tape.
There was no reason to cut 99? Also 20 is your only ground??
Please don't cut any more traces.
Please this time, list what actions you did , what it actually did?
I suspect it isn't a compatibility problem.
It might be pin 53. Please don't cut traces.
Dwight
 
Removing pin 20 was OK ( my error ).
Follow the following, remove these and leave them out, in sequence. Test after removing each chip.

I assume when you said that you remove the buffer, you meant U25 and U26
I remove jumper on J11
U21
U23
U22
U9
U19
U20
U25
U26
U24

These are all the chips that can effect the main bus, in any form. If the front panel starts working stop and let us know which chip was offending things. Most of them are inputs. If it still causes trouble with all of these chips removed ( do keep track of which came from were ) we'll need a picture of the card edge connectors, front and rear.
Dwight
 
If the only thing you can do is STOP/RUN and RESET/EXT CLEAR with a board in, it's almost always an issue of pins 70/20 being grounded on the board. Grounding pin 20 disables all of the one-shot circuits on the front panel, which disables most of the front panel functionality. I usually just cut pins 20 and 70 on the front panel card itself, since there is no known use for these signals on an IMSAI.
 
So, i removed all ICs. No changes. Then, i made tape on Pin 20 and Pin 70, now it works. I don´t understand, i cutted the trace to Pin 20 and 70, this did not work.. mmmhhh.. But, i can use the front panel again. I found some broken legs on IC 10. I removed the socket, soldered new socked and i soldered ic to another socket to repair the connections. I made the serial setup to 00h. I connected RXD and TXD on connector a. Then, i wrote the following routine:

org 000h
in FFh
out 00h
in 00h
out FFh
jmp 0000h

This should make an echo and i should see the switche setting on the LEDs. But it does not work. Then, i connected ground and TXD to oscilloscope. I have got -10,5 V. I wrote:

org 0000h
in FFh
out 00h
jmp 0000h

I should see a signal on oscilloscope, but nothing. I found the 5.0688 MHZ oscillator. The frequency jumps between some hz and 7 MHZ. I have to check for cold solder points or damaged capacitators.

THX

Jan
 
Ok. I checked BR2941 baud rate generator. It does not work correctly. Voltage and ground is correct, frequency from oscillator is also correctly now. I have to swap this IC first..


Jan
 
YES YES YES !!! It works !!!!!!!!! :)))) I have to learn better to clean this old stuff before soldering. I soldered again th baud rate generator. Now, it has signal on clock output to the uarts. I wrote my echo program again and everything is fine... :)

THX

Jan
 
Jan1980 said:
YES YES YES !!! It works !!!!!!!!! :)))) I have to learn better to clean this old stuff before soldering. I soldered again th baud rate generator. Now, it has signal on clock output to the uarts. I wrote my echo program again and everything is fine... :)

THX

Jan
Click to expand...

20 and 17 has a feed through, connecting them together. For the IMSAI, they shouldn't be connected together.
Dwight
 
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