1970 Bush CTV187CS

Hi Steve, looks in excellent condition. Glad it made it to Ilkeston unscathed.

You can easily spot early production of the A823 (and that model would have been one of them) by two holes in the rear cover where the frame hold and height pots were accessible. The very first production had knobs the user could adjust, they were about the size of a 2p coin. Later there were just two small holes for a screwdriver.

Unfortunately with the scan drive board in this orientation with the frame output transistors at the bottom the line osc coil was back to back with transductor, interaction took place causing bending of the verticals and the official RBM modification was to turn the PCB through 180 degress which completely solved the problem.

John.

Shouldn't be too difficult getting this one up and running. On the downside access to servicing is poor in parts, on the plus side the chassis is unique in the Rank sense in having a reliable LOPT. The later T20s reverted to the"Transformer murder" reputation as LL-J put it.

Been many years since I've seen one. Lots documented on this chassis. I think it was in 1977 there was a major servicing article in "Television", the issue with John Reddihough pictured on the front cover.

For initial testing connect a meter across fuse 8F3. Ensure the volts don't exceed 200V here.

Like the Philips G8 they had a long production run with several modifications over the years. Many A823 sets were still in use in the '80s, most suffering from the Teletext lines problem.

Look forward to seeing it and hearing how you get on.

The power consumption level is very good. Some early solid state sets exceeded 200W.
Cheers
Brian

Shouldn't be too difficult getting this one up and running. On the downside access to servicing is poor in parts, on the plus side the chassis is unique in the Rank sense in having a reliable LOPT. The later T20s reverted to the"Transformer murder" reputation as LL-J put it.

I must have been lucky with the T20 in my care; it was the programme selector buttons that did for that, everything else was okay!

I think it was in 1977 there was a major servicing article in "Television", the issue with John Reddihough pictured on the front cover.

I think that article covered some five months, I think! I recall one very odd fault - which my A823 suffered from - that the picture would pulsate on raw mains, but was okay when fed from an isolating transformer.

Like the Philips G8 they had a long production run with several modifications over the years. Many A823 sets were still in use in the '80s, most suffering from the Teletext lines problem.

There was an official mod that didn't work too well, and one published in Television that did. Most of these mods either involved increasing the field blanking time or trying to shorten the flyback time. Of course, that's academic now...

Many A823 sets were still in use in the '80s, most suffering from the Teletext lines problem.

There was an official mod that didn't work too well, and one published in Television that did. Most of these mods either involved increasing the field blanking time or trying to shorten the flyback time. Of course, that's academic now...

Seek the main site and ye shall find

https://www.radios-tv.co.uk/remove-teletext-lines/

Seek the main site and ye shall find

https://www.radios-tv.co.uk/remove-teletext-lines/

Rank-Bush-Murphy A823

Teletext ...

... Disconnect 4VT2 Collector and leave the leg on the component side.
Solder in the 3 additional components (33K resistor, .03uF 250V capacitor, and BA148 diode )
Replace 4R4 with another BA148 diode.

Methinks an important schematic has gone AWOL here ...

I'm excited and will be following with keen interest

Just a quick update on the Bush, as our own Marc dropped by today armed with his trusty tube tester. In my previous brief glance inside the set I'd not noticed that the A63 200X crt is a Thorn New-Life replacement. With the tester connected up, the initial readings obtained were as per the photo...

Steve

Well, you can't get much better than that !!

I think I'd call that a result...

A really good result to say the least !
Can't wait to see this shrub finished, the picture should be a belter.

Marc.

Yes, the excellent readings come as something of a relief. The set has been properly cleaned up now and looks great.

What would be the kindest way to wake it up? I read that thrysistor power supplies don't like variacs or lamp limiters. I've no idea when the set was last used and I'm not sure that some of the can eletrolytics would appreciate several hundred volts rudely interrupting their slumber.

Steve

Hi Steve. If I remember rightly with my 71 CTV197C I just plugged it in and switched on with my hand hovering at the switch ready to cut the power if anything nasty happens but nothing did go wrong . but other than checking for obvious problems i'd say just switch on and it'll either work or it wont .

Cheers
Neil.

Check as many electrolytics as you can visually for bulging on the rubber tops or any evidence of electrolyte leakage.
You should be ok and most likely all will be fine.

On first power up, don't leave the set on for more than a few moments....just long enough to see a raster, then switch it off for a break of a few mins.
Then repeat, leaving it on longer each time.

This will help re-form the caps and prevent a rapid temperature build up of the electrolyte to begin with.

Hi Steve,

You're right that many of these CTV's don't like variac's or limiters and you're forced down the "just power it on" route.

This is where preparatory checks are crucial and I normally spend a great deal of time beforehand, sometimes a day or so inspecting the boards and components looking for problems. For example on the recently repaired Aphelion I went over the entire circuit removing every module checking all the electrolytics with an E-S-R meter and replacing where necessary. Also when coming across obviously failed caps or resistors or diodes doing the same. Only then powering up.

Having worked on quite a few Thorn 3000's/3500's which equally hate variac's, my approach is to always get the power supply module on the bench and get that functioning first, nothing else is tackled until that's on spec. Once the PSU is working its placed in the set then and only then, is the whole set introduced to power.

Now I'm NOT suggesting you remove every module from your set on your first CTV repair as therein you're likely to invite trouble but, with some of the above in mind if it were me in your position, I would remove the power supply module from the A823. Then spend some time getting familiar with it, inspecting all the components in the supply rails so that you're happy they are OK. I might even suggest removing the 2x 600uF's putting them on the reformer so as to gently introduce them to power. If they reformed great, if not, then replace them. However If you don't have a reformer ( do you?) and are reasonably happy the power supply checks out OK, like Neil I would introduce it to power but with the tripler disconnected ready to quickly turn off at the first sign of trouble.

Assuming no drama after 5 mins or so, I would switch off and feel the big 2x 600uF ( be very careful when doing so not to contact the terminals) can's for over-heating. Do they seem cool? If so power on again and leave longer repeating the process until confident they were reforming or have reformed themselves. If not and at any point they start to feel HOT, replace. Once past that stage I would then connect the tripler by this time the set will have already informed you of its initial state and you will have been checking rails with your meter, you will also have noted sound or no sound. Now with the tripler reconnected raster, no raster. I/F working? Input a signal snow or no snow, tune in a colour bar or test card F, colour or no colour? If the latter disable the colour killer to see what the decoder is telling you.

You may be lucky with the set rewarding you with a good account ( you may find that a bore and want some fault finding fun) but be aware that any stage, expect the unexpected. With these all solid state sets longer use and elderly components especially those three legged beasties, inevitably start to baulk at being woken up. You may as I have found take many steps backwards from the initial state which can be frustrating, it will test your confidence and resolve to see it through.

Just my two-penneth, others may agree or disagree with the approach, either way I hope it helped.

p.s sorry to have waffled on and apologies for any unintentional egg sucking.

Edit1 : Cross posted with Andrew ( I should type quicker) looks like we sing from a similar sheet.
Edit 2: Oh and find the filter cap across the mains and remove/replace it. Only if you're like me and hate loud bangs, if not ignore and enjoy the ride

The nice thing about this particular set is that it looks to have been stored in good dry conditions.
There is plenty of space in the cabinet so during use, the heat build up would have been minimal.
The A823 is a good solid well designed and engineered chassis.
The capacitors are probably all made by CCL or Plessey and they are good quality.
The LOPT is bullet proof.
Chances are, it will power up and work perfectly.

But on the other hand, the advice given by Chris above is very valuable and should not be ignored, for the majority of sets.
It's a difficult one.....
Power up and hope, or dismantle and inpsect everything?
The problem with pulling it all apart is introducing a fault that was not there before.

Personally, I would go through the routine of what I suggested above in my previous post.....it is a compromise of a sort.

That's great advice Chris and Andrew and Neil too. My initial thought was to snip the filter cap, disconnect the tripler and go! (albeit with hand hovering over the switch!!) I don't have a cap reformer, although I would like to make one as they are a useful bit of kit, especially on occasions like this. I'lll inspect the power board closely before doing anything else. A general look around the chassis shows that there are no weeping or bulging caps anywhere, so physically it looks pretty much as-new.

An unhurried overall assessment of the set is the way to go and I'm inclined to agree with Andrew that it will probably work, although as Chris says, other faults may show up in use as it settles down.

The last A823 I owned was around 1990 when I picked up one of those Acoustic De-Luxe sets in a sort of turquoise colour from a junk shop in Nottingham for about twenty quid. Happy days!

Steve

Excellent advice already given. I would have the meter at 8F3 on the power supply panel on first test to ensure HT doesn't exceed 200V.

Cheers
Brian

I'lll inspect the power board closely before doing anything else.
Steve

Now that is a good idea

Building a cap re-former is real simple. You just need a smoothed HT supply and a 10k power resistor of a few watts to reduce the current.
Connect the cap, and monitor the current. It slowly will reduce as the cap re-forms.
I built mine from a design on Paul Stennings website.
Another project for another day.....

Back to the A823 please

As mentioned before the library ( you have an account ) holds a wealth of data to help you with the A823, from manufacturers service manual to LLJ, an excellent article from 1977 by R.W. Thomson and of course the stock faults section from the main site drop down menus.

Here's just a snippet and attention as suggested earlier, should start at the power supply it being the weakest link.