Bus resistors in STM

[Steve]

Hiyas,

I'm really bad at reading schematics (my eyes struggle) And need some assistance pointing out the bus resistors that can be changed to 2.2k for the mandatory fixes. Could anyone give me a hand? Thx

Rev H is the one I'm currently looking at:
https://www.exxosforum.co.uk/forum/viewt ... =53&t=1303

Cheers if anyone has the time,

[PhilC]

@Steve I changed all of the resistor networks to 2.2k on mine

[exxos]

Just put your meter on beeper and a middle-ish pin on any resistor back and run the other probe down the CPU pins.. you can quickly work out whats what without even needing to look at schematics.

[Steve]

Ok cheers guys, makes sense :)

[PeckPeekPoke]

Hello Atarians,

I have been removing the resistor arrays circled in this photo found here of the C070523. I believe Yellow signifies Address bus, and Red signifies Data bus.
I bought the Exxos kit and received five 2.2Ks, but this picture looks like seven are required to finish the job.
Should every single one of these that are circled (regardless of color) be replaced with 2.2k ?
Or, are RP7, and RP9 something else?

C070523-001_SILresistors.jpg

[Steve]

I only see 5 circled @PeckPeekPoke ? Where are you getting 7 from.

[PeckPeekPoke]

On the left and right of the upper-left-most ROM chip, there are two of each resistor array:
RP1, RP2, RP3, RP4, then all the others circled by the CPU and Yamaha synth-chip.
Did you put 2.2ks everywhere on the STFM you upgraded ? (It has the same mobo.)

[Steve]

Just change the circled ones ... then you have 5 .. they are the ones you're meant to swap.

[DoG]

C070522.png

I found some schematics on the C070522. It "should" be the same for C070523 I guess. Anyhow, it seems that RP2, RP3 and RP8 are the address bus and RP7 and RP9 are the data bus since they are pulled high to 5V. All of these are 10K.

RP2 is only 8 pin? (7 resistors and the common). All the others are 8pin resistor arrays. You have to check if that is the case on your board.

I really don't know why they have added som pull down resistor as well on RP1 and RP4 (4.7K). RP1 is 8pin on schematics and an additional lonely resistor (maybe R81?).

RP2, RP3, RP8, RP7 and RP9 is what we usually change on these these Ataris.

[exxos]

I really don't know why they have added some pull down resistor as well on RP1 and RP4

How odd, must be a "typo". :shrug:

This is the STM.

Capture.JPG

EDIT:

Can't really work out, but it looks like it has pullups AND pull downs on the address bus... bonkers.. maybe someone can confirm on a real ST ?