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  1. Refer to the diagram at [here...

    Refer to the diagram at [here]. Frequency changes shown in red.

    - 8288 needs a faster rating ?
    - Any fitted NPU needs a faster rating ?
    - Change to PCLK ; impact to things relying on the 8253...
  2. I found a photo online of the rear of an Amstrad...

    I found a photo online of the rear of an Amstrad PC5086.
    So a 9-pin RS232 port, which appears to be part of the motherboard.


    The TxD pin (pin 3 on the 9-pin connector) normally sits at the...
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    Using the camera on my mobile phone, the LED in...

    Using the camera on my mobile phone, the LED in my TV's remote shows quite well in normal room light, and up to 45 degrees off the center-line of the LED.

    But another remote of mine, one for a...
  4. Try the diagnostic procedure at [here...

    Try the diagnostic procedure at [here]. No keyboard required.
  5. I did some experiments a while back. The results...

    I did some experiments a while back. The results are at [here].
  6. It does.

    It does.
  7. Entering "key off" removed the black blocks, and...

    Entering "key off" removed the black blocks, and entering "color 4" showed a red block.
    Photo at [here].
  8. Suggested by Eudimorphodon at post #7 I will...

    Suggested by Eudimorphodon at post #7


    I will get onto that then report back.
  9. Supporting that: I removed the hard disk...

    Supporting that:

    I removed the hard disk controller from my IBM 5160 so that the 5160 would boot to Cassette BASIC.
    On the 5160's IBM CGA card, I removed the character ROM from its socket.
    I...
  10. Welcome to these forums. What pins are...

    Welcome to these forums.


    What pins are connected to what?


    What do you mean by "on" ?

    RS232 output signals have two levels; a positive voltage or a negative voltage. There is always a...
  11. Hopefully it will work. On the 5150...

    Hopefully it will work.


    On the 5150 motherboard, the two video switches are to be both set to ON.


    If the layout of your card matches the one at [here], then the jumper at position SW4 needs...
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    I did not notice the gap. How embarrassing. Hold...

    I did not notice the gap. How embarrassing. Hold a second whilst I look an excuse. Found it. My LCD monitor has a 'nonlinear horizontal deflection' problem, resulting in me not seeing the gap.

    I...
  13. I put a write-up at [here...

    I put a write-up at [here].
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    5-band, that colour wise, looks like...

    5-band, that colour wise, looks like |orange|black|brown|red|brown|

    Per the 'Resistor Color Code Table' at [here], 30.1 kΩ of 1% tolerance
    Example at [here].

    Looking at your multimeter photo,...
  15. For my IBM/Xebec controller (variation #3) and...

    For my IBM/Xebec controller (variation #3) and ST-412 combination, if I remove the data cable from the ST-412, there is no 1701 error at system power-on time.

    Looking at the source code for the...
  16. Before the test seeks happen, the spindle has to...

    Before the test seeks happen, the spindle has to reach the required speed.

    For my ST-225 (spindle stopped), from power-on to the final test seek is close to 20 seconds. Measured twice.
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    The partition table resides in the hard drive's...

    The partition table resides in the hard drive's master boot record (MBR), the first sector on the hard drive.

    The DEBUG program of DOS can be used zero/erase the data in the first sector. See...
  18. Like as shown at [here...

    Like as shown at [here], when the RTC chip is powered by battery, the voltage drop across the diode (a diode that is forward biased) is quite small (actual voltage dependent on diode type and...
  19. Welcome to these forums. Always good to know...

    Welcome to these forums.


    Always good to know what we are working with.

    Did the supplier indicate that the items are fully functional ?


    This needs expansion/clarification. Do you mean...
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    See [here...

    See [here].
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    When I am answering posts, I am never sure what...

    When I am answering posts, I am never sure what knowledge a poster has on the subject matter, and so I look for clues in what is written. For example, when someone writes, "When I set the EGA card to...
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    Note that when you 'set the EGA card to...

    Note that when you 'set the EGA card to monochrome', the IBM EGA card did not become a monochrome card (i.e. from a hardware perspective, not a monochrome card).

    Out of curiosity, I replicated...
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    The motherboard POST of the IBM PC will not...

    The motherboard POST of the IBM PC will not execute the initialisation code in a BIOS expansion ROM unless the ROM's 8-bit checksum is as expected. The checksum is not always for the entire ROM. More...
  24. Maybe your multimeter does not show narrow pulses...

    Maybe your multimeter does not show narrow pulses like mine does.

    But another way for you to confirm that the READY line is being asserted by the ST-225 is to:

    1. Power off the ST-225.
    2....
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    One way to see if the BIOS ROM on the IBM EGA...

    One way to see if the BIOS ROM on the IBM EGA card is being executed at power-on, is to simulate failure of one of the card's RAM chips. You will then hear '1 long beep then 3 short beeps', which the...
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