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

  1. #11

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    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

  2. #12
    Join Date
    Jan 2010
    Location
    Central VA
    Posts
    4,706

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    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.

  3. #13

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    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

  4. #14

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    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

  5. #15

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    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

  6. #16

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    Quote Originally Posted by Jan1980 View Post
    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
    20 and 17 has a feed through, connecting them together. For the IMSAI, they shouldn't be connected together.
    Dwight

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