[Central-Electronics] Central-Electronics 20A project

[Kihwal Lee]

Try injecting signal at a transmit frequency to the vfo port, instead of heterodyne signal and observe the output.  This will help you narrow down the search. 

Kihwal, K9SUL

> On Dec 30, 2013, at 4:06 PM, Alan Gutfrucht <agutfruc at chicagobooth.edu> wrote:
> 
> Hello All,
> 
> I finally got back to my 20A rebuild project recently and have run into a
> problem. I thought I was almost all done and was working on final tune up
> and the failure of the 458 VFO to triple at 16MHz (another problem) when I
> noticed that the 20A would now drop significantly in power after 5 minutes
> or so of warm-up. At startup, I was seeing 12 to 13 watts on 20M and this
> would drop back to about 2 to 3 watts indication on a Heathkit HM-102 SWR/RF
> meter.
> 
> I suspected a heat related issue so I started poking around looking for a
> burnt resistor or something that was obviously wrong. I found nothing at
> first check. Subsequently, the low power problem became permanent and
> exhibits itself right from startup. I'm seeing low power on all bands.
> 
> I am currently back at it checking all resistor values over again and have
> found nothing. Previously, all suspect resistors were swapped out along with
> all electrolytics. Some of the upgrade mods were not completed on this unit
> (serial 4345) but they have all been completed now. Initially, I had been
> through the wiring from start to finish on this checking all and found
> nothing miss-wired (but you never know what might have been overlooked). 
> 
> One thing I have noticed is that the when switching from STBY to MAN the
> relay makes immediately but the RF now lags by a half a second or so. That
> did not previously happen.
> 
> Also, in checking the voltages to the chart I see that quite a few of the
> specified negative voltages are off. For example, pin 2 grid of the 12BH7
> cathode follower it is specified at -28 volts. I measure -7 volts.
> 
> Anyways, I will be back at this over the next few days and am hoping that
> someone out there has some ideas of what I might look for. 
> 
> 73, Alan, WB2FZC
> 
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