weedeewee wrote on 2021-08-25, 21:42:
Jackal1983 wrote on 2021-08-25, 21:31:
weedeewee wrote on 2021-08-25, 20:07:What will you be using for U20 ? […]
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What will you be using for U20 ?
from the few photos I can find it seems to be a 74LS157D ?
also R19 & R20 are not present on the 512K card.
https://thumbs.worthpoint.com/zoom/images4/1/ … 839c69a1112.jpg
That pic is not coming up. I don't THINK it has anything to do with the memory subsystem but I could be wrong. Do you have a pic of the fully populated card? R19 and R20 seem to be zero ohm jumpers, not resistors, so they may need to be removed.
Oops. guess you first have to visit the site. It came from this https://www.worthpoint.com/worthopedia/wester … -vga-1792465492
I don't know if it has anything to do with the memory or not, but glimpsing at the traces, I just thought it might.
Ok, it seems like that's a later revision of the board: I think it's LH6672, mine is 1389 (might be the date code though). The PCB has a date code of Week 4 of 1990 and the main chip is from the 18th week of 1990. I can't find the PCB date coder on my card (the corresponding area is blank) but the main chip is from more than a year earlier: Week 5 of 1989. Also note that the later card has no oscillators whatsoever. I'm thinking their function is done by the ACUMOS ACLK 1 chip that's just underneath the main chip. It probably derives the various frequencies from the motherboard oscillators connected to the ISA bus. That spot is blank on my board. As far as U20, I may well just pick up one just in case unless Tiido has any idea of what that chip does.
Tiido wrote on 2021-08-25, 21:36:
50V is firmly in the diminishing returns category, 16 and 25V are gonna be enough and probably significantly cheaper.
The resistor array looks good.
Yeah, 25v is about half the price. I put that in my cart as well as a couple of the 74LS157D chips weedeewee noticed. They're only a couple of dollars. It looks like the memory modules will have to come from overseas, though. The upside is that the ones I'm looking at are 100ns (same as the stock TI Modules) Intel chips, so that's a plus I guess.