Custom interposer module for TI486SXL2-66 PGA168 to PGA132 - HELP!

Discussion about old PC hardware.

Re: Custom interposer module for TI486SXL2-66 PGA168 to PGA132 - HELP!

Postby luckybob » 2018-2-02 @ 02:02

Oh, I'm just an amateur at best. I know enough to be dangerous. I know the higher the frequency, the more it matters. I've read that as little as an 1/8th of an inch at 100mhz can knock stuff out of whack. (it was a long while ago, take with a big grain of salt.)

Bare minimum the address and data lines need to be length matched. As many VCC pins as possible need decoupling caps. Look at modern boards, wires will snake back and forth between chips and memory sticks. That's more extreme length matching.
It is a mistake to think you can solve any major problems just with potatoes.
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Re: Custom interposer module for TI486SXL2-66 PGA168 to PGA132 - HELP!

Postby feipoa » 2018-2-03 @ 02:59

I have tested the professionally made TI486SXL2-66 QFP144 to PGA132 module in various motherboards. My observations thus far are that it does not work in my one UMC 481/482-based motherboard which contains the Cyrix flush circuit on the motherboard. I'm not sure if there is some other aspect to this motherboard which causes the module not to work, or if the issue is indeed the onboard flush circuit. It does work in my UMC 481/482-based MSI MS-3131 motherboard, which, if I recall, does not contain the conventional Cyrix flush cicuit. The module worked fine in my SiS Rabbit, VIA 495, and MS-3131 boards. I have 3 more motherboards to test it it, which are the Baby Screamer, CHIPS, and SiS460. The SiS460 board is not my favourite board due to its slow speed, however, it does contain the conventional Cyrix flush circuit.

Once I've tested the commercial module on the 3 other boards, I'll start to map out the pins.

So far, the module works just fine at 80 MHz in DOS and Windows 3.11. Not sure if there is much value in trying 100 MHz. Many boards do not like a 50 MHz FSB. An interesting benchmark might be the BL3 at 2x40 vs. the SXL2 at 2x40.
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