Dumont RA-103 Project Redux

[Chris K]

What a dumb and fruitless time unless you count frustration and knowing your limitations as experience building.

The resistors came and I spent hours mounting and installing them. The area under the canohms seemed a perfect spot for bolting on these chassis mount resistors but I discovered the area was inaccessible from the top of the chassis due to the lower strap supporting the CRT. After making the appropriate changes to the layout plans, I finished the work and did a few other things most importantly, getting modern safety caps on the AC line. I buttoned everything up and began the testing. Turned it on...nothing. Panic. It was completely dead so I began investigating the AC hookup and the on/off switch and wiring. Long story short, I accidently clipped one of the wires going to the switch when I installed the caps. This chassis is a crammed full mess with hard, heat cured wiring twisted and hidden everywhere. I fixed it and began again. It powered on but my relief was short lived. When the relay closed there was no change in the amps being drawn. Obviously I had messed something up in the resistor install right? I spent several days tracing every circuit and checking the schematic over and over but I couldn't find any mistakes. I looked a square inch at a time over anything I might have moved or accidently disconnected or dropped solder on. Nothing. I even began putting together a detailed presentation for you guys with pictures of the work and the schematic detail etc. Maybe something in the relay got messed up again??? I started tracing voltages. In plane crash investigations there's something called "confirmation bias". You take an action and soon after, something goes wrong. Obviously it's something you did and you begin to see all subsequent events through the lens of your actions and focus just on that. The big picture is missed. The source of my problem with the RA-103? When I zip tied together some of the dozens of wires feeding up the side and across the chassis, I must have tied one too tightly. The wire from the choke to R285 snapped like uncooked spaghetti but couldn't be seen because it was hidden inside a wire bundle. Five minutes later it was fixed and the TV was working like it was before. Five minute fix after five days of fruitless troubleshooting over work that "obviously I must have messed up"! Well, technically I did mess it up but I lost an unbiased approach to the troubleshooting. Lesson learned...maybe. Can't make any promises on that one! More updates on progress, I hope, in the days to come now that I'm out of the self-induced quicksand.