1969 Bush CTV187CS; Single Chip Decoder A823 Chassis  

No fault with the Bush.

I thought for a test I would bring in the iMogen Testcard Generator and its modulator. The testcard and picture were perfect. Hmmm, replacing the cheap modulator with my much better workshop one resolved all the problems, no hum and no disturbance, nice clear picture.

Just shows, beware assuming faults without checking signal sources first. Time to dump the el-cheapo modulators I bought from e-bay, that's why they were cheap. 😡 You Know we really need to find a good source of modulators other than these awful ones from e-bay that require modding to a wall-wart.

I think it could do with a few minor tweaks (grey-scale and a bit of linearity adjustment) I'll run the set daily for the next couple of weeks for a good soak to see what might rear its head, don't want the damn thing breaking down on Christmas Eve. Though if it did I have spares and a choice of others sets to keep the customer (me) happy. 😉 

I was looking at back copies of PT and 2C41 and 42 can cause erratic colour control operation but you have found the problem. 👍 

Cheers for mentioning those stock faults Frank, I think over the next couple of weeks as I soak test it for Christmas, I might as well check those and others are bound to arise. 

https://www.radios-tv.co.uk/rbm-sstd-stock-faults/

Good to see you found the fault! I mostly use an old Toshiba VCR/DVD combo for my UHF signals, I also got some cheap modulators that were meant for use with satellite receivers, a couple of mods and they are good to go. I’ve also got that Chinese multi standard thing which seems ok so far, but it’s not been left 24/7 to see how it goes, I’m not sure about leaving it plugged in unattended, as the tiny mains transformer gets quite hot. 

what we could do with is an Aurora/Hedghog type box, but for 625 line UHF, maybe also with Nicam stereo! Would be nice to be able to use the old stereo sets as they were intended again.

 Regards 

Lloyd 

Posted by: @lloyd

what we could do with is an Aurora/Hedghog type box, but for 625 line UHF, maybe also with Nicam stereo! Would be nice to be able to use the old stereo sets as they were intended again.

That's a great idea, I wonder if we can persuade Frank Cuff to consider designing one. I would certainly buy a couple and I'm sure there would be an orderly queue forming should he decide to do so. 

It might be worth looking out for a professional Kathrein UHF modulator as used on internal distribution systems.

Won't be NICAM but it'll be head and shoulders above Chinese junk.

I didn't realise until now that NICAM encoding was a single chip: the NXP MC44C404.

The modulator device from NXP seems to be the MC44CC373.

Nice to see your set again Chris. I read your repair blog at the time but had the impression yours arrived pretty much up and running with little need for attention.  I still have mine, rescued from a derelict flat above a shop in Wales a few years back. It's an absolute minter but proved a real pain to get going, with even David Boynes scratching his head over some weird decoder issues. It all came good in the end but last time I switched on, over a year ago, there was a bright white flash from the rear and the set was dead. I think an ancient thermistor on the power panel had given up.  The set had already provided one dramatic firework display early on in its resurrection due to a dry joint on the 2-pin power connector to the board. Not a set for those of a nervous disposition.  Since I moved house the cantankerous old thing has just sat taking up a lot of space in a corner waiting for some enthusiasm from it's owner. Maybe now is the time, as it would nice to have Christmas in colour.

Steve

Mod Note: Posts relating to Steve's A823 have been moved to his original thread here.

There's nothing like other peoples misery to focus the neurons. I've made myself paranoid and as I'm going to be running this set over Christmas for quite some time, I'm going to take my own advice and replace the power-supply thermistor. Mine is on a hefty heat stand-off but is still looking baked compared to the NOS one. Whilst at it I'll give the entire board a thorough check out and clean-up.

A very good idea especially as your SL901 on the decoder is the especially fragile type with the tabs.

So far so good, a couple of out of tol resistors and the thermistor. Dual 2500uF cap is still good on capacitance and esr.

Board cleaned, components tested and where necessary replaced. I will put it in the Bush a little later to test.

Sigh of relief, no man made errors, power supply OK. Hopefully I will fret a little less now running it over Christmas.

That's good Chris. It gives me an excellent benchmark for refurbing my power supply board. I see that R4 got evicted too in the end.

I can see why you like BRC 3000 sets with the test rig, so you can check the supply boards are doing what they are supposed to before they go back in the set.

Steve

I do believe there was a A823 test-Rig, though none ever seem to survive.

One thing I do have which makes life a little easier servicing the A823 and I do mean a little easier, is the decoder extension kit. without one live testing on the decoder is a bit of a faff.

In knew about extension cables but not a test rig, unfortunately I had neither. Faults on the set were straightforward when in their service life so I didn’t pursue the matter.

As a cheap service jig solution the RBM service department supplied an early production 22" A823 receiver fitted with a sub-standard tube. I used one for a number of years. 

Till Eulenspiegel.

The company I worked for was heavily reliant on the A823 chassis for rental. It was supplied with two test jigs and two field service kits. I think the jig and service kit were classed as a package and so, as the service department had requested two field service kits it ended up with two jigs. I have made a rough sketch to give an idea of the layout for anyone who is not familiar with the set-up. Each of the boards was inserted into a U shaped holder which ran along guides top and bottom of the jig under the crt.

The field service kits were housed in robust wooden cases, about the size of a small suitcase opening in the same way, with the boards protected by foam inserts.

Yes, that’s exactly how I remember it and the frame was painted a light blue hammered finish.