exxos's Atari, Amiga & retro forum

so there should be continuity between that pin and pin 20 of the WD ?

also, i'm not sure what a ferrite bead looks like, or rather, what it looks like on an ST board

Ping 20 of the WD goes through the 74LS06 so you won't have continuity all the way.
You should have continuity between the WD and the 7406 and from the output of that gate on the 7406 and the pin on the floppy connecter (the filter beads are inductance so they should show as continuous if there is no AC component on the current going through).
Based on the 1040STF Schematincs :
WD1772 pin 20 ---> 74LS06 pin 9, then 74LS06 pin 8 --> bead 224 --> floppy connector pin 16 / DIN 14 pin 8

Rodolphe

what is 'bead 224' ? is it something soldered to the board? can you point it out on the pics I posted ?

spiny wrote: ↑Thu Aug 24, 2017 11:21 am what is 'bead 224' ? is it something soldered to the board? can you point it out on the pics I posted ?

He means the inductors "L". They are in a row near the ports, on your image, they look like resistors "on end". I think they are zero ohm resistors used on later boards.

On older boards there were a odd shape blue thing, they had 2 inductors with a capacitor in the center as used as a simple RF filter. Though it seems Atari removed them (maybe not needed or down to cost..) and used zero ohm links instead.

cool, so i'm looking for L224 or L24 ?

spiny wrote: ↑Thu Aug 24, 2017 11:35 am cool, so i'm looking for L224 or L24 ?

I marked the route. Looks like L224.

well, I dug out my meter and for some reason i can't find continuity on any of the pins mentioned, L224 only seems to link to pin14 on U14 and i can't find any links from L224 to any of the floppy pins.
I'll spend more time checking at the weekend I think, when I have more time. spent most of this evening rebuilding a carb for the engine i'm building for my 1978 VW Van

spiny wrote: ↑Thu Aug 24, 2017 10:24 pm well, I dug out my meter and for some reason i can't find continuity on any of the pins mentioned, L224 only seems to link to pin14 on U14 and i can't find any links from L224 to any of the floppy pins.

You should probably check from the connector to the L224 and make sure you have a connection there. Or at the very least, find the motor on signal between L224 and U14.

If you can post top view of your motherboard I can see if I have one here to double check.. Atari did move about the pin numbering on U14 a lot. So its possible the diagram doesn't exactly match your board..

Assuming you can trace L224 to motor on pin on the external connector, then at least you can confirm L224 is the right one. L224 should at least connect to one pin on U14 somewhere...

pics of the board in question:

OK so its L24 should be connected to pin 8 of the 7406 ?