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Old 12th Apr 2020, 10:00 pm   #21
1100 man
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Default Re: Bush CTV184S

Hi Mick,
Enjoyable write up as usual! I'm sure I remember seeing that set at Harpenden, but (probably wisely) decided to give it a miss!

The only A823 I've ever repaired was when I was a lad. It belonged to our neighbour. Can't remember what the original fault was, but I managed to kill the SL901 in the decoder by running the set with the board not screwed to the chassis. Rather embarrassing!

I've always found the good old A56-120X one of the most rejuvinatable tubes! Looking at how well the emission came up on the B&K, I'm surprised that you can't get a half decent greyscale out of it. That second picture does look really 'tubey' with the dingy green of the trees and pink foreground.

Reminds me of a whole batch of ex rental Thorn 9000's I bought many years ago as 'untested'. That was about the best I got out of any of them!

All the best
Nick
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Old 12th Apr 2020, 11:01 pm   #22
jayceebee
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Default Re: Bush CTV184S

In the very earliest A823 sets the field hold and height were available from the rear as user controls, later it was just two small holes for screwdriver adjustment. Unfortunately in this configuration the line osc coil was back to back with the R/G line symmetry coil and pincushion transductor on the scan drive board leading to interaction causing hooking of the verticals, the official RBM mod was to block off the holes in the back cover and invert the board. Could be tricky as the leads were very short.

John.
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Old 13th Apr 2020, 12:13 pm   #23
MickMcmichael
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Default Re: Bush CTV184S

It's true that the gray scale is a bit iffy to say the least and the photographs flatter the set somewhat. When you actually see it on the bench it's rough but a lot better than when I started. Not all three guns responded in the same way; the green gun could probably have responded a bit better than it did. Maybe Slidertogrids' bulb bopper will help....Kerpow!...Splat!

As has been said, this set was very likely chosen to be the workshop jig due to the fact the tube was shot. From the moment I saw those extended leads I sort of knew the tube might be bad. I wasn't wrong!

As always it's nice to read all the thoughts and comments. Thanks all.
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Old 13th Apr 2020, 12:44 pm   #24
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Default Re: Bush CTV184S

It shouldn't be too hard to find an A56-120. I have one with great emission on the red and blue - sadly the green pin is missing!
The SL901 used to go frequently if the earthing on the panels wasn't good. I remember killing one like Nick did. It was an important repair, so I drove thirty miles to get another. Popped it in then - where's the picture? Turned out in my haste I'd put it in upside down and, yes, killed it...
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Old 13th Apr 2020, 2:28 pm   #25
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Default Re: Bush CTV184S

All this talk of blowing decoder chips has reminded me of a common fault.. remember when the thermistor developed dry joints and the subsequent arcing burned a hole in the power panel? Unfortunately this was back to back with the decoder and often when the print finally failed with a splatt it showered the print side of the decoder board so often you repaired the hole in the power supply to find you had a decoder fault.
I seem to think this was more common on the later two chip decoder chassis. maybe the power panel PCB was more prone (flammable) on the later sets....
There was a firm (maybe DR developments) that supplied a replacement improved panel with no thermistor and I think a slow start circuit?
Like the replacement CDA panels for the Pye sets though it was late in their life and many were not worth spending the money on.
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Old 13th Apr 2020, 8:38 pm   #26
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Default Re: Bush CTV184S

I think the SL917 was in the diect line of fire from an exploding power supply! I only ever saw one of those replacement PSUs - as you say, not economic.
Hands up who has ever forgotten to connect the degauss coils with resultant clouds of smoke, usually in the customer's house...
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Old 13th Apr 2020, 9:31 pm   #27
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Default Re: Bush CTV184S

Hi.

I remember having the exact same model back in 1981 purchased from an old lady for just £10. She had just updated her main set to a Philips 1002 (K30 chassis)

I enjoyed working on that A823 which was in very good condition. The CRT had good emission thankfully. The PSU board was pretty good for its age with little sign of burning to the PCB. I always replaced the VA1104 surge limiting thermistor to avoid any future problems. I used to go through each board looking for signs of trouble and also referred to the servicing articles in Television magazine regarding known stock faults.

Access and performance on the A823 series wasn't as good as a Philips G8 or GEC 2110 but the A823 had a very reliable LOPT and EHT tray. The worst part on the A823 was the decoder. The early (single IC version) did seem better than the later (2 IC) type. Residual venetian blinds seemed to be a common problem despite careful adjustment. I since learnt that the chroma delay line can be responsible for this.
Taking voltage measurements etc were quite awkward especially the decoder and IF boards unless you had a set of extension leads.
I too remember having to replace the SL901 decoder IC on a number of occasions. The fault was often a blank/negative display. Replacing the IC was quite easy and never had any problems with damaged print.
The convergence panel fascinated me as a kid with its coloured diagram which I first saw when our A823 Rediffusion rental set was receiving attention from a field service engineer.
One thing you don't see often on other TVs is the type of EHT cap used on the A823. The EHT lead feeds in axially as opposed to the normal side entry. I do remember seeing this type of cap on another set but can't recall which.

I can't be sure but I thought that I read a tip in Television magazine pointing out reversing the scan correction panel due to interaction of line scan currents and the position of the transductor causing a disturbance on the display. Perhaps I'm imagining this but seem fairly sure I read something along those lines. Does anyone else recall this?

I also recall having to replace the mechanical tuner plastic bushes, the usual RBM problem. Happy memories though.

Regards,
Symon.
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Old 14th Apr 2020, 10:24 am   #28
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Default Re: Bush CTV184S

Replacing the IC was easy if you were the first there! I agree - the original one-chip design gave a better picture in my opinion. I never thought the later ones had the sparkle a G8 or Bradford had.
I don't think any other manufacturer used the 901/917 combination, although the unusual Z179 used an SL918. I didn't have any trouble with these decoders, but then again I saw very few in comparison.
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Old 15th Apr 2020, 4:30 pm   #29
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Default Re: Bush CTV184S

When I first entered the TV rental business in 1977, the Bush CTV184 was the backbone of my stock. They were reasonably reliable but had a few niggling little faults that were a real nuisance at times. One was poor reset on the mechanical tuner unit; another was vision buzz on sound that was difficult to tune out without upsetting the ident.
The later versions had an improved IF panel and tended not to suffer from this problem.
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