VOGONS


First post, by cyberluke

User metadata
Rank Member
Rank
Member

Hi, I bought Optiplex 433/LE and it has missing both buffer and cache.

I got 15ns cache and for buffer it should be TTL, but 74F244N is not working. No pc speaker noise, only hdd led goes on and screen will not turn on. I also tried latch version 74F643 os=r something like that.

Does anyone know what should come there?

There is one ebay seller from Bulgaria and he refuse to send me photo, he has it including the buffers. Last two months Im only buying various parts and it is not working.

I would be also curious if you could out isa vlb riser from IBM or if it is possible to make vlb riser for this board like DIY.

Here are my photos.

Attachments

Reply 1 of 11, by cyberluke

User metadata
Rank Member
Rank
Member

Adding more photos, you can see 74F245 is onboard and wired to these two buffers.

Attachments

Reply 3 of 11, by cyberluke

User metadata
Rank Member
Rank
Member

In the end 74F245N (SN74F245N Texas Transceiver LED Driver 8-Bit-Bus DIP20) seems to work, but now I have a problem with cache. I used 20ns cmos sram for both tag and cache: Alliance AS7C256-20PC. I know it supports only 128kb of cache total. I have around 20 chips total and tried to put them randomly, maybe some of them are faulty. Once it did boot into bios and it did show 120kb. But then it locks up during the boot from HDD or FDD. Then I tried different chips combinations and it never works anymore. It beeps or it locks up after BIOS POST.

Any clues? Try to order new chips? 20ns should be safe value for 486DX motherboards.

Reply 5 of 11, by cyberluke

User metadata
Rank Member
Rank
Member

I have additional photo from E-Bay.

Tag ram is MCM6265CJ15 = 15ns, probably 64k (this could be it!)

Cache looks like IDT chip 20ns (some have Alliance chip 20ns)

So that should be correct. I have tried tag 20ns (Alliance) and 15ns (Winbond) and no luck so far.

I have ordered 1x Winbond 15ns and 4x IDT 20ns now.

Attachments

Last edited by cyberluke on 2022-01-03, 17:27. Edited 1 time in total.

Reply 9 of 11, by snufkin

User metadata
Rank Oldbie
Rank
Oldbie

Hope you get it working. I just looked up on UltimateRetro just in case there was any information on it:
https://www.ultimateretro.net/en/motherboards/1593
https://www.ultimateretro.net/motherboard/manual/33432.pdf

And... no. The MicroHouse sheet shows both TAG and U55&57 as unidentified. So if you do get it working this could be a small gap filled in.

Reply 11 of 11, by cyberluke

User metadata
Rank Member
Rank
Member

Yes, it is strange. I have read that Dell & IBM motherboards of that time could have similar compatible stuff. Here is datasheet for that TAG: https://www.alldatasheet.com/view.jsp?Searchword=MCM6265CP15 and it says 8K x 9.

I have verified that U55&57 are 74F245N and TAG is MCM6265CP15. You can see that on the last screenshot above.