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SIO2SD LED driver DC/DC converter wiring?

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Went down a rabbit hole with an 800XE with a badly discoloured case and built-in Mega-HZ SIO2SD. It was all architecturally soldered with the wiring buried in hot glue, and the screen assembly had to come out for case renovation (this is the machine I ended up painting). It was impossible to document the wiring when ripping this stuff out.


Now, unlike more recent SIO2SDs, this Mega-HZ made board has headers for two different kinds of LCD module. The wiring description for the non-standard screen (the one fitted to this machine) is about half way down this page:




The LCD connections aren't a problem, but the LED backlight is - it appears - driven off a 7v supply, hence the DC/DC converter pictured below:




There are no marks of any kind on this unit and the plan was to simply jettison it and the red LCD and replace it with a modern standard unit. Unfortunately the bezels on the newer screens are too small for the hole cut in the case (leaving a huge 4mm gap), so I'm exploring the possibility of re-using the original screen pending purchase of an alternative (a Batron unit with a 30mm high bezel). The old screen is red, however, and it would be kinda nice to get it working again.


The wiring plan for the backlight makes sense to me aside from the DC/DC converter section. Coupled with the unmarked black box, I have little idea how to proceed. Anyone seen one of these before or have any ideas?


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My guess would say that it's actually dual output 15 Vdc on the side with the 3 connections (+7.5, com, -7.5). Of course the risky part is deciding what the input polarity is. If you are feeling lucky that the maker included reverse polarity protection, then just flip a coin and go for it.


- Michael

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Thanks Michael! It's something to go on for sure. I can try wiring up the backlight with the SIO2SD completely out of circuit, but knowing my luck I'll get the polarity backwards and blow the backlight on the screen. :) I tried wiring +5v/GND to the terminal pair on the other side and measuring the trio of pins, but I didn't read anything useful so far.

Edited by flashjazzcat
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If all else fails there is always the option of replacing the DC/DC converter with something new like this one which is just over $3 (free shipping): https://www.aliexpress.com/store/product/DC-DC-USB-5V-to-9-16V-Step-Up-Boost-Converter-Voltage-inverters-Module-Adjustable-Output/1525466_32264776580.html


If you remove the USB connectors it looks to be quite compact. And this solution would likely be cheaper than a new display.


- Michael

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