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Remove USB Daughterboard from 634?


New member
Hi there!

A while ago I bought both a serial and a usb version of the 634 Display series and am running it on third pary software (jalcds) ever since.

While the serial version runs for weeks nonstop without problems, the USB version crashes on a regular basis.

Here's what happens:

On startup everything's fine, the display lights up, displays the boot screen and as soon as the software is up it starts displaying screens as requested.

After a period of time varying from 60 minutes to 10 hours however the display freezes and the software reports an error "unable to write to COM3" and crashes.
After that happens the only way to reactivate the display is to disconnect the usb, reconnect and then restart the software.

As mentioned earlier the serial version (running the same screens for the same amount of time on the same machine) will run straight through for weeks of consecutive uptime without a single error, so I see the problem in Crystalfont's USB-daughterboard.

Since I have a spare com-port and experience with a soldering iron i figured it would be easiest to just remove the daughterboard and convert the display to a serial one.

Now the question:

What else (beside tearing off the daughterboard) do I have to do to convert the USB-Display to a serial one?
Do I have to open / close any of the bridges on the back of the pcb?
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CF Tech

We really do not reccommend this operation, since it is easy to damage the display. But basically all you need to do is open JPB & JPE.

Have you done any debugging on the USB side? Do you have the latest & greatest (2154b) dirvers?


New member
thanks for the quick reply!

I do have the latest drivers, that's about all the debugging I did, though. I'm more of a hardware and standards guy, I never really put much time into programming myself.

Basically I figured it would take me 10 minutes to replace the hardware and a lot more time to find out why the existing hardware doesn't work the way it's supposed to...

I don't blame CF for this situation, either, it is well possible that in my project shielding, input voltage etc are a little off standard, so my problems are probably home-made.

But fact is from the hardware side RS232 is a lot easier to deal with than USB (usually 2 doorbell wires do the trick), so I guess I'll just take the easy way out...

I thank you again for your help