10 October 2020

Kit Oscilloscope Clock 8SJ31J review - 1

Since I got few small CRT tubes without driving circuitry, I took some time to think of a good way to test them and build a display of some information. I studied circuits found online, considered building just an HV power supply and reviewed DIY kits.

The kit way sounded good, but pricey. Nevertheless, since most firmware has been written and shared, I would have spent lot of time in reinventing the wheel without breathing life to the CRT. The kit choice leaves me time to plan a nice enclosure, instead.

In the end I picked a kit from China, available on aliexpress and other sources for about 60€ delivered. It had good reviews and the design is open (I have not checked if it is derived/copied from others). The original item name is "Kit Oscilloscope Clock 8SJ31J Driver Board Oscilloscope Clock Control Board Kit Creative". The documentation says it works with a dozen CRT models, but voltages are compatible with even more tubes, like those that I have.

The kit has two boards and comes in a packaging that is safer than most other shippings from China. Instructions must be requested by mail to the seller, but what you get is schematic diagrams, one BOM per board, troubleshooting+setup tips and CRT wiring for supported models.

At this point the feeling is like building a kit you have prepared yourself with few added complications: you don't know parts placement, you need to sort-out components (easy, use a DVM!), you have no mid-build smoke tests, some values will be different or parts missing.

Regarding different values (for resistors) you can understand the reason if you can read the schematic. For empty slots on the boards you can make sense of them by looking and studying the schematic diagrams as well. In 3 missing resistor slots I fit 5 Mohm ones to give a better look. I couldn't help, my eye kept falling in that area! (Those 3 resistors are pull-up for data lines which are - in my kit - already soldered in the rotary encoder board.)

Sometimes I found hard to associate the component place with its name because the board is quite dense. In some cases the part name (R54, C11... for example) could have been moved inside the symbol and provided a paper copy of the placement for future reference. Also some pads go directly to the large ground plane and with a small pad area they are hard to solder.

Very first power-up test.

If you will build this kit use your smallest iron tip and your largest patience: there are over 400 pads on the XYZ board and over 300 in the control board!