Cpu + RTC

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

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.

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

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.

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!

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

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.

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

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