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First post, by Nexxen

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Readings: with PSU on
1. 3.3V pin of the voltage selector for SIMM ram (close to slots)
2. CS4986 chip, close by simm (see pics down), pins 1 and 48
3. mosfets readings with and without cpu inserted (single voltage i.e.)

Hello people!!

I bought this board with a P200 MMX.
https://theretroweb.com/motherboards/s/pcchips-m575

The cpu came with a broken pin that was stuck in the socket and I had to remove the lid and take it out.
Being a Vss I don't think it's dead but haven't tried it in another board yet.

The board doesn't POST.
I checked a few things and I found a broken trace near the socket, probably caused by the retention mechanism of the heatsink (the old system with hooks).

I also found a stain on some vias that scratched away in a reddish powder, no idea what kind of substance caused the corrosion.
2 are completely severed and I'll have to rebuild them.

There is no clock to the cpu. Normally I'd expect 66MHz on that pin, or the selected frequency. CLK goes to another IC: CS4968AM.
I think it's some kind of clock generator but I couldn't find any datasheet.

Board is stuck on reset, without clock it's not a surprise.

Also IC responsible for RTC I can't find no datasheet: ALi M5819P.
There are 3 Xstals and they all work, 2x 32.xx KHz and a 14.xx MHZ.

At this stage I'm stuck and have no further ideas. Unless it's the chipset and I'm out of luck.

Update: the frequency generator isn't getting the required supply, +3.3V. A Mosfet involved might be malfunctioning.
Looking into it.

My requests:

datasheets for the two aforementioned ICs: CS4968AM and ALi M5819P
Edit: found this http://biossrc.chat.ru/files/5819pb01.PDF
Edit2: https://theretroweb.com/chip/documentation/cy … 67801453944.pdf

Any help is GREATLY appreciated. Let's be bold about it 😀

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Last edited by Nexxen on 2024-06-13, 11:33. Edited 14 times in total.

PC#1 Pentium 233 MMX - 98SE
PC#2 PIII-1Ghz - 98SE/W2K

Reply 1 of 8, by Nexxen

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Cpu + RTC

RTC pfd, I still have to check if it is correct.

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PC#1 Pentium 233 MMX - 98SE
PC#2 PIII-1Ghz - 98SE/W2K

Reply 2 of 8, by Nexxen

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I made a mistake and reported the wrong voltage to the Clock Generator, the CS4968AM.
From measurements it is connected to the 3,3V that supplies the whole area, including ram slots.

Reading is 1,16V. The Mosfet responsible for this voltage is a FD3055 (supplied by PSU +5V that reads +5,20V)
S=+1,16V
D=+5,20V
G=+5,86V
https://pdf1.alldatasheet.com/datasheet-pdf/v … /RFD3055LE.html

Gate V comes from a AS431 close to it (supplied by PSU +12V).

Resistance between leads are (assuming they are correct, no voltage):
S-D: ≃3K
G-D: ≃ 3K
G-S: ≃ 6,5K

I have to replace it.

I checked fro anything too hot to be good, but I don't think anything is shorting on that rail.

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PC#1 Pentium 233 MMX - 98SE
PC#2 PIII-1Ghz - 98SE/W2K

Reply 3 of 8, by Nexxen

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PCChips rebranded/renamed everything. CS**** chip came with Cypress production markings but no reference on the net, maybe a custom production?
After finding the pinout with my multimeter...
... I dug a bit into the frequency generators and found that Cypress has a lot of CY**** model numbers for frequency generators for Pentium I/II, 686... . Looked for ALi IV and the net helped pinpointing it.
Basically they renamed the CY2273A to this CS4968AM.
The pin configuration matches -1 and -4 pinouts.

https://theretroweb.com/chip/documentation/cy … 67801453944.pdf

PCChips be damned!

To be precise, the CY2283 also matches but has a 100MHz generator, and PCChips being cheap as fudge I guess they didn't stick that one there.
https://pdf1.alldatasheet.com/datasheet-pdf/v … ESS/CY2283.html

PC#1 Pentium 233 MMX - 98SE
PC#2 PIII-1Ghz - 98SE/W2K

Reply 4 of 8, by Nexxen

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1.
I lifted Source lead and no Output.
Other two leads values' don't change.

I removed the FD3055 and tested it.
Resistance between Gate and Drain is 5K ohms.
Between Source and other two is nothing, over 20M ohms.

I deem it dead.

If anyone knows how to read the schematics, please confirm. Thanks

For good measure I ordered some new ones.

PC#1 Pentium 233 MMX - 98SE
PC#2 PIII-1Ghz - 98SE/W2K

Reply 5 of 8, by Roman555

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Nexxen wrote on 2024-03-12, 02:55:
Readings: with PSU on 1. 3.3V pin of the voltage selector for SIMM ram (close to slots) 2. CS4986 chip, close by simm (see pics […]
Show full quote

Readings: with PSU on
1. 3.3V pin of the voltage selector for SIMM ram (close to slots)
2. CS4986 chip, close by simm (see pics down), pins 1 and 49
3. mosfets readings with and without cpu inserted (single voltage i.e.)
...

Hello,
1. JP4 (both A and B) in 3.3v position - measured 3.5V on jumpers; 5V on free pins.
2. CS4968AM (48 SSOP): pin1 - 3.5v, pin48 - 3.5v (there is no pin49).
3. See on the picture
Good luck!

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[ MS6168/PII-350/YMF754/98SE ]
[ 775i65G/E5500/9800Pro/Vortex2/ME ]

Reply 6 of 8, by Nexxen

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Roman555 wrote on 2024-03-16, 10:42:
Hello, 1. JP4 (both A and B) in 3.3v position - measured 3.5V on jumpers; 5V on free pins. 2. CS4968AM (48 SSOP): pin1 - 3.5v, […]
Show full quote
Nexxen wrote on 2024-03-12, 02:55:
Readings: with PSU on 1. 3.3V pin of the voltage selector for SIMM ram (close to slots) 2. CS4986 chip, close by simm (see pics […]
Show full quote

Readings: with PSU on
1. 3.3V pin of the voltage selector for SIMM ram (close to slots)
2. CS4986 chip, close by simm (see pics down), pins 1 and 49
3. mosfets readings with and without cpu inserted (single voltage i.e.)
...

Hello,
1. JP4 (both A and B) in 3.3v position - measured 3.5V on jumpers; 5V on free pins.
2. CS4968AM (48 SSOP): pin1 - 3.5v, pin48 - 3.5v (there is no pin49).
3. See on the picture
Good luck!

This helps. Thanks!
What revision is your board? I'm trying to solve this also on discord if you want to join.

🤣 this comes a day too late as yesterday I desoldered the heck out of that board 🤣
Probably the middle mosfet is dead on my board, what's the model number on yours?

Can you give me the reading for the round IC below the mosfet on the left?
I get 12VPSU // Ground // 8.86 no cpu - 2.18 w/ cpu

PC#1 Pentium 233 MMX - 98SE
PC#2 PIII-1Ghz - 98SE/W2K

Reply 7 of 8, by Roman555

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Sorry, but now the mainboard is in a place difficult to get from.
But I suppose the schematics of LDO is pretty straightforward here and looks like on the picture.
You can try to compare it and also measure nominal of resistors.

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[ MS6168/PII-350/YMF754/98SE ]
[ 775i65G/E5500/9800Pro/Vortex2/ME ]

Reply 8 of 8, by Nexxen

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Solved, it was the FD3055.
Replaced with an equivalent it works 100% OK

@Roman555 , thanks for the help - I forgot to mention.

PC#1 Pentium 233 MMX - 98SE
PC#2 PIII-1Ghz - 98SE/W2K