Genlock failed

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Tony Jaques
Posts: 4
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: 20
Joined: Tue Jul 26, 2016 7:40 pm

Re: Genlock failed

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


Tony Jaques
Posts: 4
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: 2
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!

Tony Jaques
Posts: 4
Joined: Sat Jul 04, 2020 2:18 pm

Re: Genlock failed

Post by Tony Jaques » Tue Oct 27, 2020 1:53 pm

Hello Chris,
Thank you so much for the reply which was much appreciated, even if only seen by me yesterday (26/10/20)!
I haven't got my unit working and when a new CXA1226 made no difference it was put on one side in favour of building (in the absense of genlock) John Goode's sync reprocessor circuit from CQ-TV 136). This being prior to making (or trying to make) an S-Video version of his colour corrector from 149 - 151! For that the regenerator can be simplified a lot.
John's stuff really was good and, when you work out what each stage does in detail, very clever.
Anyway; C22 on my board was also the wrong way round, and down to 2.3uF. Unfortunately replacing it made no difference.
I did not mention before that non of the outputs from the CXA1226 are present (except for subcarrier of course).
I want to make up a temporary copy of the circuit for test purposes (rather than risk the board with a lot of unsoldering), but I can't find the 28 pin socket needed. Maybe at the next rally!!!

I sometimes wonder if I am the only one left working with "proper" video.

Thanks again Chris.
Tony...

(For a simple wanted request this is going on a bit. If the moderator wants to shift it somewhere else (as long as Chris can see it) that's fine by me.
Tony (G3PTD)

ChrisG65
Posts: 2
Joined: Sun Jul 26, 2020 8:14 am

Re: Genlock failed

Post by ChrisG65 » Thu Oct 29, 2020 1:02 pm

Hello again Tony,
Sorry hear that you still have problems. If you you need data sheets on the CXA1228S, they can be found by "Googling" the chip number. They give information for example whether a particular pin is an input or an output and what to expect.

Analogue, yes, being of that era and starting my career as a domestic TV repair engineer, I am "at home" with the old stuff. We moved house over 4 years ago but I have not yet got around to putting any antennas up. I have, however, got most of the baseband stuff functioning- that seems to take all of my spare time. I have a Cox 12 Ch. 4 bank mixer (with effects, circle and the usual wipes and fades). All transistors (Hundreds of them!) on small spine boards in individual 1U plug-in units. This is in an 18U case. Additionally there are "Engineering" switch units and Cox coders for the Cropedy Test Card Gen, and the Blue Handbook Test Card Gen (with circle and callsign). Also 3 working Tek 529 W/F monitor scopes. (In addition to the Vectorscope previously mentioned).

Let me know if I can help with some waveforms etc.

Chris. G8GHH.

Tony Jaques
Posts: 4
Joined: Sat Jul 04, 2020 2:18 pm

Re: Genlock failed

Post by Tony Jaques » Thu Nov 05, 2020 12:20 pm

Thank you Chris,
Again sorry for the delay. I have been meaning to look for a reply for several days, but I have been so busy. I don't know how I ever had tine to work for a living!
I did find the data sheet thanks (and of course I meant 1228, not the 1226 I typed). I also have quite a lot of gear, but this not the place to go into detail.
Tony

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