exxos's Atari, Amiga & retro forum

The data's getting to the 74LS74 (IC18) and pin 6 of the 556 (IC11) but not exiting the 556 on pin 5.

All the inputs to the first timer of the 556 seem nominal, so looks like that's the issue. I'll see if I have a 556 in stock.

I hope that I have some as they're no longer stocked by RS or Farnell.

Nothing in stock, not even a 555. So an order to Mouser. May get them next week sometime.

I've got loads of 555 chips, not sure about 556 though.

If its just the timer, i'm doing a order to mouser right now in fact..

Well, it looks like it's just the timer as all the inputs and voltages are there for the trigger etc. but no output on that channel.

Earlier I put in an order for 10 556s and 10 555 just for stock. You can never have too many 555s :-)

Looks like you've had a busy evening. My Mac says hello BTW 😁

:lol:

Whilst waiting for the parts to arrive I thought I'd turn my attention to the floppy drive in the FP.

It would partly see floppies when it tried to boot, either giving error 8, 4 or 99 (as it should if there's a non-bootable floppy).

Seeing as it was partly working and it depended upon the disk my working hypothesis was that it had gone out of alignment.

So I brought my F1 back from the storage and this morning removed my floppy mod so it would work with the original floppy drives and had a look. Of course, it wasn't plain sailing, Sony had shifted over to using special security screw heads by this point so the only screwdriver I could use was my trusty Swiss Army Knife. Not ideal but it worked.

Anyway, loosening the screws holding the stepper motor a little (and marking the original position) I first rotated in one direction, and things got worse. A smidge in the other direction and... success!

The drive now boots and reads floppies fine.

If I'd not had watched so many "Noel's Retro Labs" I wouldn't have known how to do this adjustment. (Then again quite often I shout "Noooooo!" at his (and Adrian's, and Jan Beta too) videos when he does something. :-) )

Found a couple of 14 pin sockets so decided to de-solder the 74LS74 and 556.


They were a complete sod to get out.

Not only was there a designed in bodge with that diode (which appears in the schematic) but the manufacturer had bent all the pins of the ICs tight to the circuit board before soldering them! It took a lot of efforts to get them out with the Hakko FR-301, soldering iron, braid and hot air. Still I made it in the end.

The legs of the ICs were a mess, but I managed to straighten them out enough to get them in the sockets.

I refitted the diode on the back of the board.

Phew!

When the 556 arrives, possibly tomorrow, it'll be an easy job to pull the original and replace it with a new one, then we can see if that fixes the problem. The only other parts in the area are some passives and TR1.