Ok, I think I found something after the second inspection with magnifying glass. It is in SIMM slot 1, Bank 0. Surprise - two bent pins. These were really hard to spot:

I'll straighten these bent pins with fine tweezers. But now I'm wondering why the board wouldn't boot and complained about memory (single long "beep", "C6, C1" POST codes) with two memory modules installed in Bank 1.

I'll test the board tomorrow (just to be sure it's completely dry after the "bath") and hope the memory issue will be resolved and there will be no more "surprises".

P.S. Bent pins straightened and back to their places. I think bent pin 5 was in contact with pin 4 (both are data pins) and maybe this is the cause for memory error when SIMM modules were installed in second memory bank - Bank 1.

majestyk wrote on 2024-05-31, 06:34:

This should be easy to test: Remove all cache chips, the TAG chip and any inserted COAST module. The system would start without error - IF cache was the problem.

I almost forgot. Here it is the only COASt module that I have. SMART IN364TCSP83YG15, 94V-0 with two Sony CXK77W3211Q-12C SRAM chips and one Cypress CY7C185-15vC (8K x 8 ) SRAM chip:

I don't know if this COASt stick will be compatible with SY-5TCxx motherboards. I was looking for Vcc and Vss pins in the COASt slot on the mobo and I gave up when most of the pins in one of the sides of the slot turned out to be Vcc.

majestyk, if yours SY-5TC is still at hand, can you give me the markings/values for the missing VRM U42 and the two missing SMD resistors near U42 - R106 and R107, please? Just in case if my board starting to work properly, so I may hardware-upgrade it to a newer revision.

It lives, again! 😀

First successful POST after the "bath" and SIMM slot 1 bent pins repair:

Something funny here: This is the first Pentium-class mobo I've ever seen with BIOS that has fading away EPA logo effect as in the 486 Award BIOSes. Maybe this effect is only used in Award BIOS version 4.50PG.

Now I have to complete the ext. battery holder mod. And of course I'll try the newest available BIOS for this board modified with BIOSPatcher 6 and MODBIN.

Many thanks to Mr. Steunebrink (Chkcpu), Brightraven, majestyk, Sphere478 and all other participants in this thread, who made me "bath" this mobo and give it a second inspection!

P.S. I will not risk to install my only COASt module in this board until someone confirms that they're 100% compatible.

analog_programmer wrote on 2024-06-01, 10:08:

majestyk, if yours SY-5TC is still at hand, can you give me the markings/values for the missing VRM U42 and the two missing SMD resistors near U42 - R106 and R107, please? Just in case if my board starting to work properly, so I may hardware-upgrade it to a newer revision.

Glad it´s back to life!
The integrated VRM is a "PQ30RV31" (Sharp), R106 is 430R and R107 is 261R.

majestyk wrote on 2024-06-02, 10:19:

Glad it´s back to life!
The integrated VRM is a "PQ30RV31" (Sharp), R106 is 430R and R107 is 261R.

Thank you for giving me this information about the missing components! The datasheet for this VRM is available online, I'll try to find some suitable replacement.

A good find, the bent SIMM slot pins and Great to hear you got the board fixed! 😀

Having provisions for a CPU VRM as well, this board would be a good candidate for Necroware’s S7-VRM module. Then you could max it out with a K6-2+ at 400MHz! 😉

Cheers, Jan

Chkcpu wrote on 2024-06-02, 12:01:

A good find, the bent SIMM slot pins and Great to hear you got the board fixed! 😀

Having provisions for a CPU VRM as well, this board would be a good candidate for Necroware’s S7-VRM module. Then you could max it out with a K6-2+ at 400MHz! 😉

Cheers, Jan

Thanks for all the help, Jan!

Yeah, the external VRM module for the CPU will be an easy mod - a matter of soldering a couple of male 2.54 mm pin headers. The hardest parts of this task will be to find one of those MMX CPU VRM modules (I've never seen one "in person") and to find the jumper settings for using it. But this board has great potential in support for s.7 MMX CPUs and even AMD K6-III+/2+ CPUs. The only drawback is its lack of SDRAM support.

But now first things first. I have to finish the RTC ODIN external battery mod.

My tinkering with this board ends here: Re: Socket 4, 5, 7 BIOS image collection

So, this is one nice ancient s.5/7 piece of a motherboard for those who can get/make suitable VRM module for dual voltage s.7 CPUs. The VRM module presented in the Necroware's YT-channel (I'm not sure if this guy's nickname here is "scorp") seems promising: https://github.com/necroware/s7-vrm