A1200 problem with display issues during floppy access

[mykrowyre]

I have an ESCOM 1D4 A1200 which shows screen wobble during floppy access, and every 20 seconds or so the screen will jump. This always happens on the drive click. If I insert a disk, it stops.

What I have done:

Watched 5V rail, and it dips about 150mV on each floppy tick on my scope (at least best I could measure). I can see it in the video output, both composite, RGB sync, and pin 23 on the RGB connector. Some dips are deeper than others and the deeper ones cause momentary loss of video.

Measured 5V rail, seems low @ 4.82V. Replaced the power supply with an ATX power supply, and a new aftermarket supply, voltage didn't change.

Removed all hardware including floppy drive. Voltage still around 4.8V.

Checked for a cap at 215. It's there. The 1.2V reference voltage for the decoder is perfectly stable.

Installed a .1mf cap across pins 1 and 13 of the CTX1145. This is also the same as installing a cap in C460. Read that a commodore repair tech said this was a fix from commodore in 1995 or so. This had no effect.

I replaced all the electrolytics, no improvement.

Disconnected the 5V to the RF modulator. No change in voltage.

Tried installing caps from .1uF to 100uF across the 5V rail at the floppy drive power connector hoping to smooth out the floppy pulse, no improvement.

Checked capacitors in the Panasonic floppy drive. The appear OK but I could not disassemble to test them. Couldn't figure out how to remove the PCB and the zero track sensor is on the PCB so did not want to go further.

Looked for any sign of damaged components or traces, everything looks good there is no corrosion.

So short of removing and checking every single SMD cap that is across 5V and GND, does anyone else have any ideas?

I could just install NoClick but the display would still jump when accessing the floppy which is a no go for me.

I do not want to replace the floppy with a GoTek, I enjoy using floppies.

The main clue seems to be the lowish voltage on the 5V rail at 4.8V, sometimes 4.78V. I would expect something like 4.92V but I am not really sure.

I can only conclude that something (bad cap?) is pulling the voltage down from 5v to GND so I checked temperatures across the main board and can't find anything getting warm. I just hope whichever cap it is shorts soon so I can find it!

Thanks for any ideas in advance!

[stx2199]

4.8v is ok
the only way to reach 5.0v It is cutting the power supply cable making it shorter

try another floppy drive
or use the RGB video out instead composite

[mykrowyre]

Originally Posted by stx2199

4.8v is ok
the only way to reach 5.0v It is cutting the power supply cable making it shorter

try another floppy drive
or use the RGB video out instead composite

I'm not using composite, I'm using RGB and a 1084s, but a different floppy is worth a try.

[stx2199]

Originally Posted by mykrowyre

I'm not using composite, I'm using RGB and a 1084s, but a different floppy is worth a try.

yes try an original Amiga drive not a PC modified drive