exxos's Atari, Amiga & retro forum

Late delivery of some of the axial mainboard caps just arrived ..so looks like a busy soldering day ;)

Ok...replaced all the 47uf capacitors in the sound stage....and in the process found some corrosion spots..
..and also an open circuit trace that connects one of those caps to pin 26 of U508.
problem was i couldnt attach a bodge wire to R 531 (51k) corrosion again.
Managed to get R531 off the pcb eventually ..but it broke in half in the process.
Easy enough to replace if I had one.
Obviously there is reason wht 51k was chosen..so now I have 5x 1/2 watt 51k resistors on order as well.
I could have just fitted a 56k but figured Id wait till the replacement arrives before it gets powered up again.
Besides which I still have other electrolytics to replace and I aint rushing this.
rgds
VS

My friend paid me a visit today and brought with him a small bag of resistor packs..
amongst them was a nice 9 pin 8 + VCC array..
Just fitted it onto the disc controler chip.
Looks good to go.
I will of course check for shorts to VCC > GND and adjacent pins.
I figured this was the best solution for VCC ie the common pin.
rgds
VS
...I must remember to tidy up the resistors on U305

Had a think about U305 which is modded by connecting 5 pins to vcc by 5 1k resistors...
Because the pins that need 1k to vcc are staggered ..this to be seemed a neater way to do it using a 8x 1k resistor array...
I dont know if 6 way ie 5 pins plus common vcc exist...? but I didn't have such a thing anyhoo so used a 9 pin but didnt use the 3rd and last 2 pins ..just bent them out of the way..
rgds
VS

I did a little PCB for that chip a while ago with 0805 SMT resistors. But it's a lot of work to get it to look neat. Here you can see it finished and in place on the motherboard.

I did the PCB with resistor at the bottom. The gerbers attach is two different version. Resistors on top or at the bottom.

DoG wrote: 10 Feb 2026 22:42 I did a little PCB for that chip a while ago with 0805 SMT resistors. But it's a lot of work to get it to look neat. Here you can see it finished and in place on the motherboard.

I did the PCB with resistor at the bottom. The gerbers attach is two different version. Resistors on top or at the bottom.

Floppy_fix_2020-07-19_Bottom.zip
Floppy_fix_2020-07-17_Top.zip

Certainly better than a bunch of random 1/4 watt resistors..
Nice neat job :)

Now I'm hoping this doesn't cause me issues...but I needed to mount a switch for the TOS switcher externally accessible but to be as unobtrusive as possible.
I found the smallest latching switch I had and mounted it here..see pictures.
Where have other members mounted switches on their Atari ?

First time power up since the mainboard recap...
Fingers tightly crossed that I hand't introduced a fault in that process.
Ran up a coppy of Loom I wrote to disk with Omniflop.
Appears to run ok but a fault ? I had before the recap was still apparent.
Is it a fault or a monitor incompatibility ?
I was hoping this would be cured by the re-cap.
roughly every 10 to 15 seconds there is a slight dimming of the display..nothing actaully crashes or changes but is annoying.
any thoughts would be most welcome.
Oh...just to add..the cpu doesn't even remotely get warm to the touch..
If I had to guess..one way of confirming the HC credentials of the chip I bought ?

Vipersan wrote: 12 Feb 2026 14:07 roughly every 10 to 15 seconds there is a slight dimming of the display..nothing actually crashes or changes but is annoying.
any thoughts would be most welcome.

I've only seen that with bad monitor connections, or when the floppy drive is reading, the stepper motor causes a slight voltage drop which causes the monitor brightness to dim. On some machines its worse than others and the PSU brand can also be factor.

exxos wrote: 12 Feb 2026 14:43

Vipersan wrote: 12 Feb 2026 14:07 roughly every 10 to 15 seconds there is a slight dimming of the display..nothing actually crashes or changes but is annoying.
any thoughts would be most welcome.

I've only seen that with bad monitor connections, or when the floppy drive is reading, the stepper motor causes a slight voltage drop which causes the monitor brightness to dim. On some machines its worse than others and the PSU brand can also be factor.

Cheers for the useful info..a starting point at least..
I'll get a scope on the video signal and monitor its amplitude for deviations I think.