Thread: Mk14 vdu
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Old 1st Jun 2020, 8:26 pm   #29
Timbucus
Octode
 
Join Date: Mar 2019
Location: Barry, Vale of Glamorgan, Wales, UK.
Posts: 1,362
Default Re: Mk14 vdu

Well as requested - the short story is here are the mods I did to get a nice clean composite on my Phillips CRT. Basically the manual BOM has to have R9 and R7 changed and the omitted R6 needs to be installed - C10 is still omitted.

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Note that I was unable to tune the modulator - I have since swapped it for another and still cannot on either my Phillips or my period Sony - the latter does give a poor picture.

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It is possible I need to revert the component values to allow the use of the modulator - I was unable to find its DataSheet UM1233 but, maybe it needs the near 5v p2p that the system was putting out that was blanking my usual desktop CRT. Martin has said that his LCD works with the original values on composite - it does not seem to mind the higher voltages.

The composite image on my Phillips is great though!

For completeness of mods done: I have bent up b27 (as that would short the clock to a GND on the b side so a wire patch underneath (tiny one, one pad down from the resistor) takes it to XOUT on the 'a' side where it comes from the MK14.

The resistor is for the pullup for NWDS which is mentioned in the VDU Manual as needing to be done on the MK14 - note that changes to NENIN have already been done on the Slothie V6 board - you would need to do those on a real one or the JMP/Martin clones along with the pullup. I did it on the clone VDU as it is removed when I unplug it.

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Finally the two white wires (and the associated bent up pins, move b13 the VDU ON/OFF from connecting to PA0 on the INS8154 I/O chip to FLAG1 (on pin b1) as recommended in the manual - I prefer this as you can turn it on and off (which you need to do to use cassette or a KeyProgrammer) still without an IO chip (I have used patch wires in its socket to pull the relevant pins up and down) - and it is canon from the manual - I may well hook my Graphics/Chars (b14) over to Flag2 for a similar reason.

The other wire is the Reverse Pages pin which I move from INTR (an input to the IO chip) onto PA3 which can be an output.

My next step will be to make a neat 8154 plug in module with some switches for the other lines and try my actual 8154 to change things within a program.
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