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Old 27th Apr 2018, 12:50 am   #36
Slothie
Octode
 
Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 1,287
Default Re: MK14 schematic revisions

Yes. a guy in California was selling them (I think it may have been the one you pointed out) so I bought 4. They arrived Thursday! So I have those and some 65X61 chips, and there is a link on the bottom of the board to select which type (they all have to be the same type).

If John can find his 7408s then I have a source for all the chips!
I just need to get my PROMs programmed; I have the schematic for the MK14 prom programmer, which I could hook up to an arduino. I just need to be sure it works first time because I only have the two!! Did I see you say you had a 74S571 programmer? could I ask you to program them for me if I sent you the PROMS and return postage?

The 7408 has a 130 ohm resistor in the output (see schematic) which would limits the current through the LED to about 25ma, which multiplexed 8 ways is an average of ~3ma which is the correct sort of average current for the LEDs in the bubble display.
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