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1969 Bush CTV187CS; Single Chip Decoder A823 Chassis  

 
crustytv
(@crustytv)
Vrat Founder Admin

This A823 console was working fine back in 2013.

With my 70's lounge now finished it was time today for a first time power up in 7 years in preparation for use this Christmas. Pretty much working but has developed a couple of quirks during its slumber time.

  1. Colour control goes from B&W to colour to B&W from lowest extent to maximum extent of control.
  2. There seems to be a lot of disturbance, almost like sound on vision.
  3. Bit of a hum too, not intense but can't say I noticed it before. Main 700uF cans are cool to touch.

 

Some Photos:
Mainly showing the good condition of all main boards. hardly any dust either for 7 years of slumber.

rbm1
rbm2
rbm3
rbm4
rbm5

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Posted : 16/11/2020 2:57 pm
PYE625 liked
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crustytv
(@crustytv)
Vrat Founder Admin

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.

NFF
CTV187CS

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. 😉 

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Posted : 16/11/2020 4:54 pm
colourstar and PYE625 liked
Nuvistor
(@nuvistor)
Famed V-Ratter Registered

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

 

Frank

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Posted : 16/11/2020 5:17 pm
crustytv liked
crustytv
(@crustytv)
Vrat Founder Admin

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/

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Posted : 16/11/2020 5:45 pm
Lloyd
(@lloyd)
Noble V-Ratter Registered

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 

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Posted : 16/11/2020 5:47 pm
crustytv
(@crustytv)
Vrat Founder Admin
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. 

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Posted : 16/11/2020 7:13 pm
Cathovisor
(@cathovisor)
Illustrious V-Ratter Registered

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.

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Posted : 17/11/2020 12:28 pm
colourstar
(@colourstar)
Honorable V-Ratter Registered

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

Bush1

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

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Posted : 17/11/2020 4:38 pm
crustytv
(@crustytv)
Vrat Founder Admin

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.

a823pwr1
a823pwr3
a823pwr
a823pwr4

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Posted : 18/11/2020 1:51 pm
Jayceebee
(@jayceebee)
Noble V-Ratter Registered

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

John.

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Posted : 18/11/2020 2:44 pm
crustytv
(@crustytv)
Vrat Founder Admin

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

pwrtest

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Posted : 18/11/2020 2:49 pm
crustytv
(@crustytv)
Vrat Founder Admin

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

refurb1
refurb2

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Posted : 18/11/2020 4:26 pm
crustytv
(@crustytv)
Vrat Founder Admin

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

powerefurb

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Posted : 18/11/2020 4:55 pm
Lloyd liked
colourstar
(@colourstar)
Honorable V-Ratter Registered

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

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Posted : 18/11/2020 5:21 pm
crustytv
(@crustytv)
Vrat Founder Admin

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.

A823extn

 

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Posted : 18/11/2020 5:32 pm
Nuvistor
(@nuvistor)
Famed V-Ratter Registered

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.

Frank

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Posted : 18/11/2020 7:18 pm
Till Eulenspiegel
(@till)
Famed V-Ratter Registered

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.

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Posted : 19/11/2020 11:24 am
rbmt20a
(@rbmt20a)
New V-Ratter Registered

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.

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Posted : 20/11/2020 12:19 pm
rbmt20a
(@rbmt20a)
New V-Ratter Registered
20201119 204806
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Posted : 20/11/2020 12:22 pm
Jayceebee
(@jayceebee)
Noble V-Ratter Registered

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

John.

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Posted : 20/11/2020 2:02 pm