Monthly Archives: March 2016

Kepco JQE75-1.5M PSU refurbishment – Part 2

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So I continue my refurbishment of the Kepco JQE75-1.5M PSU.

My LED displays arrived from Ebay so I decided it’s time to fit them, and time to replaced the neon power indicator with an LED.


I could not find a stable voltage (as in, not changing when adjusting the current/voltage pot) so I opted to find an AC voltage either on the board or on the transformer itself.

After 2 attempts I found an unused 24Vac winding on the transformer and hooked up the following circuit to the LED display and power LED which replaces the neon bulb.



(Note: there is a 330uF 50V electrolytic reservoir cap across the DC output voltage I forgot to draw in)


This seems to work fine, now I just need to fit an IEC connector and a bezel for the LED display on the front panel.

2016-03-19 01.08.00

How I reverse engineer digital circuits

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2016-03-12 19.56.14

It’s been a while since I’ve posted to my blog, but here is a video I just uploaded showing how I reverse engineer digital circuits.

I’ve been doing this sort of thing for as long as I can remember and I find it very relaxing at times. Nothing better than throwing some nice music on and doing a bit of reverse engineering.

I was recently given a dot matrix LED display by a friend and decided to reverse engineer it so we both can run them, he still has one of his own.

There is a damaged chip on the board which meant that some of the displays didn’t display their 2 bottom rows but I will be tackling this issue in a later video. I will also be transferring the control to a PIC instead of the Arduino as it was not fast enough to get a good refresh rate, and this is without any external communication facilities being addressed.

Here is the video:

The arduino sketch can be downloaded here

and the Design Spark schematic file can be found here

the PDF of this file can be found here

*There are a few parts not finished in the schematic, but there is enough to provide functional detail.

I hope you enjoy the video, I will eventually follow it up with the repairs and the porting to PIC.

bye for now!

Kepco JQE75-1.5M PSU refurbishment – Part 1

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I found myself some PSU’s at a flee market a few weeks back and decided to pull out the matching pair of 75V PSU’s for some inspection. Much to my delight, they both appear to work fine.

The only issues with them is the neon power indicators are not working (or barely working), and the voltage/current multiply switches for the analogue movements are crusty. And not to mention a non-standard power connector on the rear. These will all be replaced and updated in future videos.

I have decided to replace the analogue meters with LED modules (just waiting for them to be shipped from China on the slow boat) then I will hook them into to sense the output terminals and find a way to recess it in places of the old meters.

For the power indicator, I will find a voltage rail inside the PSU (most likely an opamp rail) and fit an LED in place of the neon lamp.

Please keep tuned for more!

You can subscribe to my YouTube channel to get updates on my progress too.