haxor wrote on 2022-11-09, 23:07:

POST card is not displaying any codes

The previous owner desoldered the dallas 12887 (which was probably empty) but did quite a mess with bad solder joints. I didnt touch this area yet, only checked if the socket had continuity to somewhere near (74L chips). Seems they have contact except for pin A3 - no idea where its going or if its connected at all. The traces are buried below the socket and i'd have to desolder the socket to find out where its going. Tried area around it but couldnt find anything where it connects to.

I can tell you BIOS might not want to progress without/with malfunctioning dallas chip, but no post codes means your bios doesnt execute at all.

haxor wrote on 2022-11-09, 23:07:

Unfortunately the bios chip is soldered to the board. I'd like to only desolder it if neccessary (to prevent stress to the board). I am not sure if above problems could be caused by a missing/defective bios.

scope bios cip select/ output enable pins, address and data pins, see if any data is read from EPROM at all

haxor wrote on 2022-11-09, 23:07:

The previous owner desoldered the dallas 12887 (which was probably empty) but did quite a mess with bad solder joints. I didnt touch this area yet, only checked if the socket
had continuity to somewhere near (74L chips). Seems they have contact except for pin A3 - no idea where its going or if its connected at all. The traces are buried below the socket
and i'd have to desolder the socket to find out where its going. Tried area around it but couldnt find anything where it connects to. Anyone know if this is used at all?

Here’s a photo I took when I desoldered the Dallas chip from my Batman’s Revenge board. Hope it helps!!

rasz_pl wrote on 2022-11-10, 04:38:

BIOS might not want to progress without/with malfunctioning dallas chip, but no post codes means your bios doesnt execute at all.

scope bios cip select/ output enable pins, address and data pins, see if any data is read from EPROM at all

I've scoped all pins from the eprom. Chip select and output enable are high once powered up and stay high. The data and address pins do all show signals (on some i see 60 Mhz signals on others different).
How would i know that there is actual read activity to/from the eprom?

TheMobRules wrote on 2022-11-10, 09:52:

Here’s a photo I took when I desoldered the Dallas chip from my Batman’s Revenge board. Hope it helps!!

3D1EDF35-42D4-4B7C-AD41-0BFF856475B6.jpeg

Thanks alot! This helped to check the traces - they are fine. So i can outrule the dallas as the culprit (for now).

haxor wrote on 2022-11-10, 11:36:

rasz_pl wrote on 2022-11-10, 04:38:

BIOS might not want to progress without/with malfunctioning dallas chip, but no post codes means your bios doesnt execute at all.

scope bios cip select/ output enable pins, address and data pins, see if any data is read from EPROM at all

I've scoped all pins from the eprom. Chip select and output enable are high once powered up and stay high.

pins 20 and 22 of BIOS _must_ both be low at the same time for successful bios read

rasz_pl wrote on 2022-11-10, 13:18:

pins 20 and 22 of BIOS _must_ both be low at the same time for successful bios read

are you sure? The board has a intel n28f001bx chip (plcc 32). PIN 20 on that chip is D6 and 22 would be CE (chip enable).
Just checked the datasheet and it appears both CE and OE should be low for successfull operation/execution. I assume you mean these two?
So there must be something driving these high...any idea where to look for?

haxor wrote on 2022-11-10, 20:11:

n28f001bx chip (plcc 32). PIN 20 on that chip is D6 and 22 would be CE (chip enable).

ah yes, different footprint, 22 and 24

haxor wrote on 2022-11-10, 20:11:

Just checked the datasheet and it appears both CE and OE should be low for successfull operation/execution. I assume you mean these two?
So there must be something driving these high...any idea where to look for?

they are driven high by default, and both go low only when chipset decodes memory read from BIOS address space access
you can look at maybe similar design in intel 430HX reference design https://usermanual.wiki/Document/intel82430hx … .1819793331.pdf

mercury chipset https://pdf1.alldatasheet.com/datasheet-pdf/v … EL/82378ZB.html doent have dedicated romCS output? seems page 114 shows 74F138 decodes and generates this signal

>This register enables/disables accesses to the RTC, keyboard controller, floppy disk controller, IDE, and BIOSlocations E0000–EFFFFh and FFF80000–FFFDFFFFh. Disabling any of these bits prevents the encoded chipselect bits (ECSADDR[2:0]) and Utility Bus transceiver control signal (UBUSOE#) for that device from beinggenerated