The capacitors are 0.1µF, and look to be 0805 parts.

I'm not sure what the resistor array has to be but it seems it should 8x individual resistors, and possibly using same value as the two others nearby looking to be 33 ohm. No clue what the package is called other than SOP16 of some sort.

Tiido wrote on 2021-08-25, 07:03:

The capacitors are 0.1µF, and look to be 0805 parts.

I'm not sure what the resistor array has to be but it seems it should 8x individual resistors, and possibly using same value as the two others nearby looking to be 33 ohm. No clue what the package is called other than SOP16 of some sort.

Thanks. I figure I can grab the info off of the other arrays when the card arrives and hunt down whatever is closest. Any idea on the voltage rating for the caps?

Anything past 6.3V is usable, higher is better with these ceramics.

Tiido wrote on 2021-08-25, 07:03:

The capacitors are 0.1µF, and look to be 0805 parts.

I'm not sure what the resistor array has to be but it seems it should 8x individual resistors, and possibly using same value as the two others nearby looking to be 33 ohm. No clue what the package is called other than SOP16 of some sort.

Ok, so it looks like it's essentially this resistor network:
Bourns Inc. 4816P-1-330LF
https://www.digikey.com/en/products/detail/48 … emSeq=374896202

I'll order most of the parts after I verify that the card actually works. I'll wait on the modules themselves till i've installed the sockets, caps, and resistor network (in case I screw up and brick the card). Do you think I'll need to reflash the bios or should everything "just work" once I've got the parts in?

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

weedeewee wrote on 2021-08-25, 20:07:

What will you be using for U20 ? […]
Show full quote

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. The pads lead to a series of 5 unused pads on the back of the card so a pic of the back might be useful as well.

Tiido wrote on 2021-08-25, 18:57:

Anything past 6.3V is usable, higher is better with these ceramics.

Ok, so the 50V parts I have in my cart at digikey are overkill? https://www.digikey.com/en/products/detail/CL … emSeq=374885058

50V is firmly in the diminishing returns category, 16 and 25V are gonna be enough and probably significantly cheaper.
The resistor array looks good.

Jackal1983 wrote on 2021-08-25, 21:31:

weedeewee wrote on 2021-08-25, 20:07:

What will you be using for U20 ? […]
Show full quote

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.

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 ? […]
Show full quote

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.

You could just check if there's any traces connecting the ram to the chip. If there are, chances are the chip is needed for more ram.

weedeewee wrote on 2021-08-25, 22:28:

You could just check if there's any traces connecting the ram to the chip. If there are, chances are the chip is needed for more ram.

Problem is, some of those traces terminate underneath one of the resistor packs, and that part of the board has some big honking ground plains in that area. Also the traces are a pain to work out on this thing: the board itself is a greenish tan color and the traces almost blend in! The chip leads could be connecting to the resistor packs in that area underneath the packs and going on to the memory. I'll investigate further before I order.

Update: Found another pic of the same board with everything populated except the modules themselves. Looks like U20 has something to do with memory after all. I'll order the chip (dirt cheap from Digikey) as well. The main chip is simply WD's rebadge of the original PVGA1A-JK, not a different chip. It looks like the R19 and R20 jumpers will need to be removed as well.