exxos's Atari, Amiga & retro forum

Hi people,

I've got two faulty ST's, both Rev B ST's. On the rear of the shifter socket they both have different resistor/capacitor bodges, can anyone here clear up which is correct for this revision?
Thanks,
Steve

For orientation, ram is at the bottom of each photo.

Image1: a single resistor 1k or 10k? and a capacitor
Image 2: only one capacitor

I think original Atari factory hardware mod ...

What are the Shifter Pin numbers? IMP or normal chipset?

Thanks @frank.lukas
Ah yes.. sorry I always forget these are capacitors.

Image 1:
Shifter: C025914-38 / PH23-023 CAP
1k resistor (Shifter pin 1 to GND)
capacitor: yellow violet black gold black (Shifter pin 21 to GND)

Image 2:
Shifter: C025914-38A / PH23-024
capacitor: yellow violet black gold black (Shifter pin 11 to GND)

See the schematics ...

Steve wrote: 12 Aug 2021 11:14 1k resistor (Shifter pin 1 to GND)

Seem normal (10K on the H5 in fact)

Steve wrote: 12 Aug 2021 11:14 capacitor: yellow violet black gold black (Shifter pin 21 to GND)

BLUE bit 2... Odd to have capacitors in the blue line like that, maybe it was just inherently more noisy on that colour :shrug:

Steve wrote: 12 Aug 2021 11:14 capacitor: yellow violet black gold black (Shifter pin 11 to GND)

/LOAD. Again probably noise.

Overall by the looks of it, these bodies are probably just tailored to whatever board has whatever problem after manufacture.

capacitor: yellow violet black gold black

4 7 x1 5% ?

47pF

Ok, thank you guys. So it seems they're perfectly fine to keep as-is.

Just as a follow up to this thread I decided to try these capacitors on another ST with poor video output:


But even after applying these capacitors nothing changed and the video output is still poor, with all those vertical white and black dotted lines. Does anyone have more suggestions on what else I could try to smooth out the image quality / reduce noise?

Its a inherent problem which a lot of early STs suffer from :? All you can do is add something like 10uf ceramics on the power on the shifter and rgb drivers and 47pf from RGB on the video connector to gnd.

exxos wrote: 17 Aug 2021 20:32 Its a inherent problem which a lot of early STs suffer from :? All you can do is add something like 10uf ceramics on the power on the shifter and rgb drivers and 47pf from RGB on the video connector to gnd.

Okay cool, just to clarify for my feeble mind:

• 10uf ceramic on Shifter 5v pin to GND
• RGB drivers, are these Q5,Q4,Q3,Q2 transistors? If so am I connecting 10uf from base/or/collector/or/emitter to gnd on each one?
• With the 47pf, is that three 47pf's, one on each line R,G,B connected to gnd. At the video connector.

thx