Genlock failed

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Tony Jaques
Posts: 2
Joined: Sat Jul 04, 2020 2:18 pm

Genlock failed

Post by Tony Jaques » Mon Jul 06, 2020 7:02 am

Hi there,
In CQTV 174 (a quarter of a century ago!) Peter Delaney produced a slaving SPG design. This used a CXA1228S IC which is a TV decoder. Just this week my unit stopped genlocking, and that IC has no outputs so the SAA1101 has nothing to lock to, and the NE567 sees nothing valid, of course.
The CXA1228S seems to be practically unavailable. Even the chinese don't make it! So of course I am wondering if anyone happens to have one that they could sell to me to rescue the project.
Failing that, does anyone else still have this SPG, with the IC on a socket so that they could confirm that my IC has failed
- and it is not me being stupid!

Thank you for resding this anyway.
Tony
(G3PTD)
(and was G6ACW/T even further back!)

aerostar
Posts: 17
Joined: Tue Jul 26, 2016 7:40 pm

Re: Genlock failed

Post by aerostar » Mon Jul 06, 2020 8:23 am


Tony Jaques
Posts: 2
Joined: Sat Jul 04, 2020 2:18 pm

Re: Genlock failed

Post by Tony Jaques » Wed Jul 08, 2020 8:58 am

Thank you for the reply aerostar.
I had not seen that one. I hope that he returns from wherever he is before the item ends on the 24th!
Actually I have also now received a reply from an apparently American company, with a Chinese address.
They want about £20 for 10 of the things, which is little more than the absentee wants for one. So if he doesn't return
I may buy those and dump 18!
Thanks again
Tony...

ChrisG65
Posts: 1
Joined: Sun Jul 26, 2020 8:14 am

Re: Genlock failed

Post by ChrisG65 » Sun Jul 26, 2020 10:15 am

Hello Tony,
I hope that this gets to you in time, straight to the point. I also have same SPG, just got it out after many years packed away. Same problem as you. Works for a minute or so when cold then lock lost. Changed CXA1228S- No change. Long story short- check polarity of C22, 22uF. The board is marked the wrong way round !! The + should go to pin 27 and have about 2.6V on it, other end 0V. With new cap, now it's OK.

As well as the 4.43MHz xtal I had also changed C44 and C45 for non- electrolytics as they seemed a bit temp. sensitive. I've now run out of freezer! I had a spare CXA1228S. (Just as well as the original broke when "gently" prising it out!)

Best wishes,

Chris Gibbs. G8GHH. (ex G6ALR/T). Keeping shack warm with 51 valves from my TEK 526 Vectorscope!

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