[Heathkit] SB-610 focus problem

[Dave Cook]

Thanks Patrick. Yes, I Googled also and had already found the first page you
mentioned below.

And yes, I've replaced all of the electrolytics except for the C603 can
(which actually means I only replaced C600 and C601), the two .1 and the one
.15 uf'er in the HV supply, the selenium rectifiers with a pair of two
1N4007s in series, and the R605, R508, and (as I already mentioned) R510 in
the Intensity/Focus resistor chain. While I was in there I replaced R504,
R505, and R506 for good measure, and I think I might have replaced R503, but
I'll have to check. So given that I've replaced all the components,
including the CRT, and with the exception of the pots, I'm not sure what
else to try. The intensity, horizontal linearity, and vertical sensitivity
are all good. The only exception is, as I noted, the focus control was all
the way to the right until I replaced R510 with a 3 megohm resistor chain.
So that's all the details. I'm assuming that the ceramic and mica caps are
probably ok, but maybe they might be suspect?

> -----Original Message-----
> From: heathkit-bounces at mailman.qth.net [mailto:heathkit-
> bounces at mailman.qth.net] On Behalf Of Patrick
> Sent: Wednesday, May 26, 2010 9:26 PM
> To: heathkit at mailman.qth.net
> Subject: Re: [Heathkit] SB-610 focus problem
> 
> 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
> 
> 
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