I bought this oscilloscope from a mate for very few dollars as it only
had one beam working. He had bravely bought it on Ebay from another
country. It is dual trace 20MHz and features a single shot sweep
A search of the web revealed no pictures or other information about it
so I have given it a place on the web. If you have a problem that I may
be able to help you with please contact me via my index page.
I have done a lot of fault finding on digital circuits but know very
little about fixing CROs but at least I had one beam working so I had
something to copy from. I downloaded a manual with a circuit from
another brand of about the same vintage. This revealed the general
principals of how a CRO worked and the sort of circuit that I might
The symptom was no beam 2 in normal operation but if both beams was
selected 2 traces appeared. If a signal was put on the good beam it was
reflected at half the size on the other beam. However no signal showed
if a signal was put on the bad beam. My first idea that a switch was
faulty was dashed when I found from the downloaded representative
circuit that the switches only provided logic levels to a bunch of
gates and the all important flipflop that switched between beams.
A heap of diodes do the actual switching and I suspected that one was
shorted or o/c but no luck there.
I could get to the solder side of the vertical board and see most of
the other side but I was having trouble tracing and remembering just
what solder pad connected to what when I had the idea to take a picture
and print it out. It would then be easy to pencil in the components and
get an idea of the circuit.
This worked like a charm and I improved on the method by
photographing both sides of my next repair project then
fliping and combining the images and making the component picture semi
transparent. It was like having Xray vision.
When checking the beam switching diodes I noticed that the
voltage on the faulty channel was near the +12 volt rail so
the hunt was on to find where this spurious voltage came from. Tracing
backwards lead me to a 14 pin package a CA3086 that thanks to
Google I found was a 5 transistor array. Some metering proved that it
no longer contained any transistors. Problem solved.
Using a digital camera to help trace a circuit.
A composite photo showing the Xray vision effect.
My next fix was a megohm insulation tester that had no high voltage. It
was easy to photograph both sides of the board and use my photo
editing software (The GIMP) to flip the parts side picture, place it on
to (with some stretching and rotating) the track side picture and
the transparency of the top layer to get a result, part of which is
shown above. It could have been improved by making some of the darker
components individually more transparent but it was OK for a first
effort. My printer is not colour but the printout was useful. If
I added another layer I could have drawn resistor symbols and such over
the top of the components then deleted the component layer and be left
with a very useful and easy to read result.
The above method requires experience with a photo editor but simpler methods give good results.
attempt to fault find a glow plug timer I photographed the solder side
of the board and with IRFANVIEW ( a popular free simple photo editor) I
flipped the picture horizontally, lightened it and printed it to fill
an A4 sheet. All very easy with IRFANVIEW especially the printing.
symbols could then be drawn in rapidly by hand as their location agreed
with the printout. The hard work of understanding the circuit
could then begin but made simpler by the easy to follow component
connections. Fault finding can be done from the component side with no
turning over the board to follow tracks.