JX30 VL-Bus Motherboard issues

[kishy]

Originally Posted by lutiana

I do not have an EPROM programmer, so I will need to either leave the cache disabled or find another way to test them.

Any idea on where one can buy new chips?

I have some cache chips I've yanked off stuff in the past, I'll check the numbers for you when I'm home again later.

Edit:

9 chips
28-pin DIPPs

UM61M256K-15
95330 N70218

Not sure if these could help you but if so let me know.

[lutiana]

Originally Posted by Chuck(G)

Nope--it's just the bare RTC/SRAM chip, the original animal as used in the 5170. It'll keep ticking as long as you care to replace batteries. A set of AA-sized alkaline batteries should last at least 3-4 years easily.

Interesting. Must have been switched onto the board at some point, all the documentation I can find on it says:

The JX30 Motherboard does not require an external battery to be installed.

The Dallas / Benchmarq Real Time Clock Chip contains an internal battery for an approximate lifetime of 8-10 years.

But no matter, the external battery I jerry-rigged is working fine. Its amazing what one can do with some electric tape, aluminum foil and a few bits of wire.

[Chuck(G)]

You can get a 4 AA battery holder at Radio Shack for under $2.00. Might hold together a bit better than tape and foil.

[lutiana]

Originally Posted by Chuck(G)

You can get a 4 AA battery holder at Radio Shack for under $2.00. Might hold together a bit better than tape and foil.

Yes, it will. I intend to, but when I rigged it Radio shack was very much closed

But my tape job will most likely hold for a very long time actually, it would just be a pain to change batteries.

[kishy]

Originally Posted by lutiana

Yes, it will. I intend to, but when I rigged it Radio shack was very much closed

But my tape job will most likely hold for a very long time actually, it would just be a pain to change batteries.

Ah yes, I've done the "battery holder made of tape" thing before too. Just don't use $0.50 electrical tape, it tends to melt even at room temperature.

[lutiana]

Does anyone know if these work as cache replacements?

I simply cannot find any of the chips that are actually on the board.

[Chuck(G)]

They look close enough. I wouldn't have thought that 32Kx8 high-speed SRAM shouldn't be too hard to locate. But maybe the "window" has passed?

How about this one from Jameco?

JDR's got some too, but they're about $6 the each.

[lutiana]

So according to this the TAG chip is by the ISA slots, and it is a different chip (a tc5588p-20). It appears to be an 8kx8 chip.

One thing I don't understand is why there are 10 slots for SRAM chips on this board. The one marked U200 seems to be the odd one out.

Do i need all 10? Could I pull the chip from U200 and put in the tag slot (and leave U200 empty?)

[Chuck(G)]

I suspect the cache is parity-checked.

You can use a 32Kx8 SRAM in the tag socket, regardless. The pinouts are compatible--it simply won't use the extra memory.

[lutiana]

If you look at this picture:



You will notice that there are 9 sockets by where the cache chips are and the TAG chip is up my the ISA slots.

I took the ninth chip (the odd one out) and switched it into the tag chip slot removing the 8kx8 chip. It worked! I know have 256kb of write through cache.