[Heathkit] SB-610 focus problem

[Patrick]

Dave Cook wrote:
> Ok, I'm at my wit's end here and have to beg for some advice. I have two
> SB-610s, one of which has very good focus and the other one is significantly
> defocused at the edges of the trace. I researching previous questions about
> this on this reflector, the suggestion was to refurbish the HF power
> components and replace all of the original resistors in the intensity and
> focus supply chain. I've done that and the situation did not change at all.
> I've even swapped out the CRT with, again, no improvement. Furthermore, I
> found that I couldn't quite achieve focus even after replacing all of the
> resistors in the HV chain with new ones, and could only improve that by
> replacing R510 (3.3 megs) with a 3 meg resistor (three 1 megs in series). I
> don't have a way of measuring that high of a voltage with my DVMs, so I'm
> not sure if it might be a voltage problem. Any advice would be greatly
> appreciated.

Did you try this:

Focus problem
The CRT now had plenty of voltage and showed a green line although it 
could not be focused properly. The resistor between ground and the focus 
control had increased in value. Replacing it solved the focus problem.

 From this page:
http://oak.cats.ohiou.edu/~postr/bapix/SB610.htm

I'm not sure if this was included in your "focus supply chain" resistor 
switch-out or not...just something I ran across doing a Google on the 
problem (sorry if you have already seen this page...just trying to help 
out).

Also another page addressing focus problem:
http://www.radiobanter.com/archive/index.php/t-115295.html

One problem I have run into while restoring old video games (the big 
arcade type) is fuzzy displays. I can typically correct it by changing 
out the electrolytic caps (since they are usually quite old) and the 
display will be sharp again (I don't know if it will help in your case 
or not).

Patrick KA4ZNU