Quote:
Originally Posted by Doug66
. . . .
I started recapping the electrolytics and paper caps, and I got the raster almost full, but no signal yet. When I ordered the last electrolytics, I also decided to replace the 2 candohms R178 (1650) and R 174A (1500).
When I tried a power up after this, I had no raster and no B+. I have checked and rechecked all my work and even disconnected everything from the filter choke, then connected it up one by one.
. . . .
|
There is a fair chance that you made a connection error in replacing the components. The old saw, about one never seeing their own mistakes, is true here. Ironically one of the two most difficult sets to repair and the cause of my most wasted time back in the 1950's when I was learning TV servicing, was a Hoffman 7JP4 set where they omitted a CandOhm bleeder resistor on both the schematic and the parts list. This component proved to be both open and shorted to ground. To keep heat away from sensitive parts, it was located on the opposite side of the chassis to the circuit to which it connected and I had missed it in my circuit checking. Ironically, neither Sams nor Rider had my schematic, but there was one factory attached inside the cabinet and it was incorrect!
I don't know where you found your schematic, but the drawing of the power supply is unnecessarily complex.
So you can look at the circuit with fresh eyes, I'd suggest that you go to the ETF website and download the Rider schematic for the 610 Hoffman, and print out pages 15 and 16.
http://www.earlytelevision.org/tv_sc..._diagrams.html
(The Sams schematic on ETF shows a more robust power supply using two 5U4's and is also marked "preliminary", so I'd avoid that one.)
While you have the full Riders, verify that you are looking at the correct model and chassis number.
The first thing to check is the connections to the resistors in the focus network, as these resistors and focus coil setup the different negatives in the power supply. Also do a visual inspection for solder bridges, especially terminal to case on the candohm, and cold soldered connections in the power supply. On both the focus coil and power transformer, sometimes just wiggling the wires can accidentally open the connection where the solder flux has weakened the copper.
Don't worry if some electrolytics are a slightly different value or a different physical mounting, just check the polarities.
Hope this helps.
James
Edit: In addition to Old Coot88 & UserName1's good suggestions, I left out test 101 !
When powering up, look at the plates of the 5U4 in reduced lighting. If they start to turn a dull red, the set is drawing too much current. If the 5U4 plates stay their original color, there is probably a high resistance or open connection somewhere.
If the plates indicate too much current, it will do no harm to yank the Audio Output V105 to see if it corrects the B+ problem, in the remote chance that tube has shorted while you were rewiring the set. Otherwise, it probably is an inverted electrolytic or an incorrect connection.