[Sticky] My video source rack.
Nice set up, enjoyed the read.
Well thank you Doz I'm very glad I read that and followed the link to the article on your UHF modulator. I recognise that pcb all too well... I have one here which also suffered a very similar breakdown a few months ago. I'd been using it with a Fidelity colour portable as a sort of stop-gap set-up when I had just moved house. It would have been winter and it's possible the atmosphere in the living room was slightly on the damp side as I had the door from the lounge to the kitchen open and there were pans on the hob.
Suddenly there was a loud crack from the Fidelity and the frame collapsed. I suspect that the moisture in the atmosphere had caused the LOPT to arc over and deliver a mortal blow to a chip (this chassis had a reputation for that sort of thing!) Just as I was taking that disaster in there was a really nasty outbreak of snapping and cracking from the UHF modulator which had me diving for the plug to bring the whole affair to an abrupt end.
Judging by the experience of Doz I'd say the insulation in the tiny mains transformer had also succumbed to the slight rise in atmopsheric moisture content. Using an external wall wart supply is a great idea so I'll try that to see if the modulator still has any life left in it.
^ The wounded Fidelity.
It must have been a damp room to have that effect on them both.
I had a similar set for a few month last year & the service manual is available online, which might help sort it out.
Hi Richard, the room wasn't exactly like a Turkish sauna but I suppose it had just enough extra moisture to cause the tv a problem. Maybe it was just coincidence that the modulator picked that exact moment to self-destruct.
I've now carried out the patent Doz power supply conversion on the dead modulator using a spare Nokia phone charger and it works a treat. His unit had exactly the same symptoms as mine. The article is here:
As to the tv, those that consider Fidelity products as cheap tat are quick to suggest it's instant tip-fodder but I'm reluctant to throw out one of the dwindling number of 80s UK-made portables.
Incidentally, there is another UHF modulator around that looks externally the same as the ones referred to above, but has a lower component count. It does however use the same tiny transformer. Probably another candidate for an external DC power supply.
Great advice Andy for improved modulator safety 👍
I run two modulators for my analogue service, chan 56 (iMogenTeletext/Test Card generator) & chan 60 (Programme/VHS/DVD). Just modified the chan 60 modulator, it took all of 10mins to complete. As you rightly point out, very little work for a great deal of improved safety. Now off to see if I have another spare wall-wart to do the other one.
I think this thread which also includes the link to your excellent blog post, should be a sticky, so it is.
Before work came to a halt I was in the process of converting a 12G SDI video to HDMI converter to external PSU operation: despite only being about four years old the PSU had keeled over and the thing ran quite hot too.
I must confess I don't like external PSUs one iota, but I can see their advantages over bare-minimum internal supplies like these. Once upon a time, bulk DC distribution was the norm at work.
I had (may even still have) a variation of that set but with remote control. In its case the 33V stabiliser had died and greatly upset the operation of the big IC in it that handled tuning and memory.
Most notable was the on-off switch which had a solenoid release, thus ensuring the set really was off when you pressed the button on the remote!
Thanks for the lovely comments. If anyone fancies building the multiplexer, I have a few spare, unpopulated PCBs spare if you'd like to have a go.
Nicely done Andy, and a sight smaller than the two Quartz video and audio matrices I have!
Very nice setup, far better than my lash up.Blog was a very interesting and informative read.
Now off to see if I have another spare wall-wart to do the other one.
No need !! I'm a "der-brain", I'd forgotten that the modulator I use for my chan 56, had been replaced with a slightly more upmarket (read expensive) one that uses an external power supply.
The original one serving CH56, was another CCT811 that went pop like Andy's, a couple of years ago. I repurposed the case to build a thyristor tester.
Before I bought a fully switchable modulator I used to use modulators designed for use with early Sony Play Stations and 1990s Japanese camcorders. These can be powered from a USB connector, but the Play Station ones are fixed onto channel 36.
The Canon camcorder modulator can be changed between channels 30 & 39, so I can use them together.