I was recently contacted by forum member Mikro, who had read my 1084S monitor repair thread, and asked if I would be willing to take a look at his Atari SC1435 monitor. The Atari SC1435, which is virtually identical to the Philips CM8833 MkII, was working fine until one day the picture collapsed and was never to be seen again. The power light was still lit however. I decided I'd like to get more experience with these things, so I arranged to get the monitor from Mikro, and began to troubleshoot it. Initially I disassembled the unit, and resoldered key joints such as flyback, HOT, switching transformer, yoke. Then reassembled I began to take some test measurements. Using the high voltage probe I built last year I was seeing only around 13kV on the picture tube - pretty much half what it should have been (should have been around 25kV). Checking the power supply B+, I was seeing just 68V (this should have been around 125V) : Many of the other power rails were approx half what they should have been, but the power supply section all checked out otherwise. I disconnected the B+ supply before the flyback, connected a load (lightbulb) and re-tested - supply voltages were normal : Thus it was quite possible that the flyback transformer was at fault, dragging the power supply down, but I had no way to properly test it. I'd read about ring testers before - a ring tester applies a pulse to the flyback transformer primary circuit, and counts the number of damped oscillations or 'rings' produced : "`Ring' testing gets its name from the fact that when a fast pulse is applied to the primary winding of the LOPT, the total inductance and capacitance in the circuit will produce an electrical `ring' - a decaying AC voltage which can have a duration of a dozen or more cycles before it reaches a low value. It's the electrical equivalent of tapping an empty glass; in each case, an energy impulse generates damped oscillations." The ring testers that I had seen had 8 LED's - the idea being that if it lit up all 8 LED's then the transformer was likely ok, but if it only lit up a couple then the transformer likely had internal shorts in the windings. Dick Smith used to sell a ring tester kit which was designed by Bob Parker: Luckily, Bob Parker has kept all documentation for this ring tester kit on his website here, including the assembly manual, PCB artwork, and mirrored artwork for toner transfer methods. So, I decided I'd build one using the documentation that was available, and etching my own board. The finished article (I'll put it in a case at some stage!) : I used the toner transfer method but was a bit lazy cleaning the board beforehand, and the transfer was a bit ugly. A couple of tracks had small breaks in them after etching - Thus i went over the whole pcb with a bit of solder and repaired the breaks : Main thing is it works! Testing the flyback in circuit across the primary coil on the flyback : Only 3 LED's were lit on the tester, which is not a good sign : I also hooked up the scope - the ringing waveform : Testing another transformer - all LED's lit up as they should: And the scope trace : This is pretty much what the flyback trace should have looked like - a gentle attenuation with plenty of "rings". Incidentally, this is the pulse that is injected : Thus the flyback was classified as faulty, and removed. I was able to order another one from WES which I should receive later today The old one : I'll update this thread once I've installed the replacement.