Epson HX-20 - Collective brain help required :)

[stephen_usher]

Unfortunately I can't find where I bought the battery. I think I threw the delivery note last year.

[rubber_jonnie]

Unfortunately I can't find where I bought the battery. I think I threw the delivery note last year.

Not to worry, I appreciate you trying, thanks.

[HigashiJun]

Found this:

https://www.batterymart.com/p-p130scr-4 ... ttery.html

and the battery looks like this:

battery.jpg (147.33 KiB) Viewed 687 times

Hope that helps.

[rubber_jonnie]

Found this:

https://www.batterymart.com/p-p130scr-4 ... ttery.html

and the battery looks like this:


battery.jpg


Hope that helps.

Sadly they look US based and I think it'll be a bit expensive with VAT and tariffs. I've ordered some sub-c cells to build new packs for both machines.

Interestingly I have done some more digging and it seems like the original is stuck in a sleep state because it beeps but the display never starts up.

I need to look deeper into that as it seems reasonable that it could have either a bad sub CPU which drives the wake signal or possibly the transistor controlling it is bad.

More investigation to come.

[HigashiJun]

Sadly they look US based and I think it'll be a bit expensive with VAT and tariffs.

Yes, that's the drawback when buying from the US while being based in Europe...

[stephen_usher]

This should work: https://www.thebatteryshop.co.uk/tbs-4s ... 8174-p.asp

[rubber_jonnie]

This should work: https://www.thebatteryshop.co.uk/tbs-4s ... 8174-p.asp

Thanks, I'll take a look if my battery pack builds go sideways

So I have been following the power up sequence and so far so good, including getting a power good signal but power to the CPUs is a bit all over the place, voltages are not steady, so that doesn't entirely make sense.

I have clocks to both CPUs and reset is working too. A lot is good it seems, but something is failing in the power circuit, at least that is what seems to be happening because the LCD never powers up, but I do get a beep.

More tracing of the circuit I think.

[stephen_usher]

You're powering it from the battery socket I guess.

[rubber_jonnie]

You're powering it from the battery socket I guess.

I am indeed.

[rubber_jonnie]

OK, so a day of discovery with the HX-20's - Yes there are two now

Number one is the worst, it doesn't give a proper power on double beep and the display is blank, however I did manage to do some extensive diagnostics today and I know the following:

1. The power circuit checks out with the power on sequence working as per the technical manual, including the power abnormal signal correctly showing power is good.
2. The RESET circuit also checks out as expected.
3. Clocks are good.
4. The master CPU is showing activity on the address and data lines and it looks normal.
5. The slave CPU doesn't show any activity on the address and data buses, but I need to cross check with the 2nd machine - more on that shortly.

In addition to the checks above, I found 2 leaky caps:

IMG20260504144228.jpg (159.74 KiB) Viewed 644 times

IMG20260504123720.jpg (195.18 KiB) Viewed 644 times

Luckily the boards seem pretty robust and it was enough to clean up and then add some fresh solder mask before replacing the caps:

IMG20260504144246.jpg (313.04 KiB) Viewed 644 times

IMG20260504123744.jpg (247.76 KiB) Viewed 644 times

As for the 2nd machine, I get a proper double beep and I see garbage on the display, however it is notable that from time to time I see the system menu and sometimes even with garbage on screen at a steep angle you can see the display is showing the menu.

Hitting menu items seem to show the monitor program (This might mean a RAM issue) and hitting CTRL @ brings up the date/time setting menu ((As best as I can discern).

So I believe it is running (Mostly) and I think that it may have a RAM issue, but since it has a RAM expansion I need to double check the dip switch settings to be sure it's not expecting external RAM that isn't currently there.

I need to go through the tech manual thoroughly as it is possible that the first machine is stuck in sleep mode. There are some troubleshooting flowcharts that may get me through this.