A few years ago Richard Diehl kindly made me a SPG circuit for my Sony portable vidicon cameras, when I tried it with one and the picture was vibrating so there was some problem there so I stuck to using the UTEL SPG for my vidicons. After digging it up I thought I'd try it with my Iconoscope camera and it actually worked good in comparison to the vidicon cameras so have decided to replace the big UTEL SPG/pattern unit and mount the SPG circuit inside the camera. So that's one less piece of bulky equipment needed to run the camera! :) Here below is the SPG and output buffer mounted inside the metal platform the Iconoscope bulb end sits on:
Now as mentioned in the above vlog I am now ready to move onto working on adding horizontal/vertical centering control to the camera's timebase deflection circuit and presented the schematic Richard Diehl provided for me. I realized that the schematic doesn't have the vertical centering control mod so will start with the horizontal. Also included is a another width control circuit powered from a LM317 afjustable regulator. So I modified the deflection board's horizontal drive implementing the circuit mods in Richard's schematics. I roughed togther the LM317 circuit for the width control and I used the +/-12V regulated power supply I made a while back with a 1K pot and load resistor connected to the horizontal output to adjust the horizontal centering.
After implementing Richard's circuit mods I fired up the camera and got no picture but was getting video output from the video circuit. Details on the result can be seen in my vlog below:
The next day I started on trouble shooting the issue of the circuit mod. I connected the horizontal output to the scope and was getting the horizontal output wave and adjusting the centering pot I was getting some action on the waveform so it appeared to be working. But I found that the horizontal output waveform was peaking at a much much lower voltage than it was when the camera was outputting a picture and so I figured that was the reason why I wasn't getting a picture. I was gonna demonstrate the waveform in this vlog below but disaster struck, the centre tapped +/-12V/15V transformer went bang on the primary side so I quickly switched the camera off!
While I made that video I didn't know what blew so I was a bit stressed but didn't take long for me to figure out it was that transformer mentioned above. Somehow it was drawing more current than it can handle which is 1.83A max! I later found out what actually caused the transformer to draw excessive current and will talk about it later but at this point in time I thought I simply had too many voltage regulator circuits connected that transformer to power the circuitry. So my next move was to either find another 15V centre tapped transformer that has a higher current rating or get the company I used to work for to make me a transformer, I chose the latter. I got the company to build me a single transformer that will output all the voltages needed for all circuits so it will replace the three transformers I have in the camera and of course with much higher current rating, so at a decent price they kindly built me one! :) The transformer specs are as follows:
Outputs: 6.3V 10A, 30V, 15V-0V-15V centre tapped
Next thing to do is remove the other two transformers and do some rearrangement to accommodate the big transformer. I decided to mount the -1KV power supply on its side to make more space which I cut some pieces of scrap metal to screw the power supply on and screw mount to the enclosure. I mounted the transformer to the front left side of the camera and beside it made a solder on terminal section for the multiple outputs from the centre tapped 15V windings. I also had to add an extra switch to the rear panel due to the setup of the transformer so the first switch switches on the 6.3V heater winding, the second the 15V centre tapped windings and third the 30V winding.
It's now time to put the tube back into the camera and fire it up again and pick up where I left off. So I put the tube in, fired up the 6.3V heater winding and let the tube heat 5 min, all good there, then fired up the centre tapped 15V windings and immediately heard a fizz and saw smoke billowing out the opposite side!!! I immediately switched off the power and looked over the side where the smoke was and it turns out one of the wires going to the little 12V power supply I made to power the SPG has fried and so has the rectifier as it was shorted out.
At that point I thought maybe the wire just couldn't handle the current so I replaced with thicker wire and replaced the faulty bridge rectifier and fired it up again and same thing happens the wire smokes up so switched it off. I then decided to remove that 12V power circuit and connect the SPG power leads to the + output of the +/-12V power circuit and fired up the 15V centre tap winding and no smoke no bangs, all sweet! Then I fired up the 30V winding, it powered up and I was fine for a little bit but then I saw smoke coming from the timebase board and it turned out to be the 270 ohm resistor connected between the LM317 regulator circuit's output and the 100 ohm pot overheating!
I just started to realize with that little 12V circuit I made, it couldn't just draw max current from the transformer but just the required current to function unless something was really faulty with it, I believe I must of wired it up incorrectly somewhere, I won't use that circuit no more! It now has become clear to me how that other transformer blew up, that faulty 12V circuit drew a lot of current, more than the transformer could handle! Now that that problem is solved, next problem to sort out is that overheating 270 ohm resistor and why I am not getting enough horizontal drive to produce a picture! I decided for the horizontal width control to revert back to the previous setup that worked, so I removed the LM317 regulator circuit and the burnt 270 ohm resistor and put a big high wattage 39 ohm resistor in place and the 1K pot with 100 ohm resistor in parallel for the width adjustment and I fired up the camera and I got a picture again :) and the horizontal centering actually works!!! :) It was of course not without more problems, the horizontal width was wider and the 1K pot to adjust the centering overheated and smoked! And there was a problem with the picture as I was getting a thick rolling shade bar rolling down the picture nearly completely fading the picture to black intermittently and also the contrast of the picture is really poor too!
I then decided to disconnect the horizontal centering control pot and see if the picture looks as normal as it did before the modification and the picture looked mostly normal and I can adjust the horizontal width to get the full picture but I am still getting a shaded horizontal bar moving down the screen.
After I uploaded the vlog to YouTube, Richard and someone else commented that I am likely getting mains hum in the video amp circuits and that I should check the capacitor filtering and earthing. There's a chance the size and power rating of the transformer might have something to do with the hum as well. Next time I work on the camera I will be checking the earthing and capacitor filtering and go from there in fixing the hum issue.
So that's pretty much where I am up to with my Iconoscope camera, it is slowly evolving and I hope within the next year I will have horizontal/centering adjustment, blanking, keystone correction and a mostly noise free picture! Stay tuned! :)