General Stuff(tm)

[stephen_usher]

Thinking about this I may replace R36 with a combination of a 720 ohm resistor and a trim pot. This should allow the +5V rail to be tuned both up and down as necessary.

[rubber_jonnie]

Thinking about this I may replace R36 with a combination of a 720 ohm resistor and a trim pot. This should allow the +5V rail to be tuned both up and down as necessary.

I really don't like PSU's that can't be trimmed, so that sounds like a good plan to me.

[stephen_usher]

The trim pots I had were too low current it seems and anyway, whatever resistance I used I could only ever get the loaded +5V down to 5.15V, which is still too high. I'd have liked something like 4.9V to be safe.

At the moment I've got it bottoming out at 5.30V with fixed resistors.

[stephen_usher]

It turns out that the bulb on its own wasn't loading the power supply enough.

The bulb and the hard drive together load the PSU enough that I have full control of the voltage via my trim pot.

IMG_3587.jpeg

IMG_3589.jpeg

[stephen_usher]

So, what did I change in the power supply?

Replaced R36 (2K2) with a 1K8 resistor.
Removed R37 and replaced with a 2K potentiometer.
(R32 wasn't fitted, looked to have been removed after manufacture.)

[stephen_usher]

The AY-5-8116 chips have arrived so I can see if it fixes the Kaypro serial clock issue.

Seeing that both the SIO and 8116 were bad, who's betting that the crystal's OK?

[stephen_usher]

It works!

IMG_3590.jpeg

Even Drive A booted first time... But copying to Drive B failed at track 7 (reading from A, not writing to B!)

[stephen_usher]

Bother, the Z80 SIO/0 I ordered from Little Diode turned out to be a Z80 DMA when I opened the packet. *sigh*

[stephen_usher]

More shenanigans with the Kaypro drives this morning.

Drive B's motor decided to run full speed whatever I did, even replacing the LM2917 on the servo control board.

I'd already reflowed the solder on the connector, which had cracks. So it was a case of buzzing out traces.

Found that an old bodge to repair where a capacitor had been pushed through the board and pulled the trace off the board wasn't working any more. It was extremely ugly anyway. So I removed it, put a proper bodge wire across the board, secured by hot snot, and resoldered the leg of the capacitor to a better piece of the trace.

That worked.

Put everything back together yet again... and Drive A started playing up. *sigh*

[PhilC]

@stephen_usher you have my sympathies. I’ve been working on an Opus Challenger 3 in 1, got the ram working now but the drive spins up but doesn’t step whilst trying to format or read.