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1970 Bush CTV187CS

Pre War 240/405, Post War 405 Line, B&W Dual Standard, Colour Dual Standard, B&W S/S 625, Colour S/S 625 line, Hybrids. Standards converters & modulators, video recorders.
 
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Re: 1970 Bush CTV187CS

Post by CTV » Mon Aug 15, 2016 10:29 am

stuie319 wrote:A white 'acoustic deluxe' sleeps in my cellar, albeit in poor nick.

Stu

If you ever decide to move it on Stu there's a nice warm spot in the North. A set high on my list along with unicorn dust :qq1

 
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Re: 1970 Bush CTV187CS

Post by davidh1041 » Mon Aug 15, 2016 3:18 pm

Hi Steve, a couple of things I would have a look at before powering it up. There is a 47k across each smoothing block in the middle of the chassis, these tend to go low in value and put a big stress on the PSU, also check the print around the TH7 thermistor on the PSU panel, sometimes it cracks and can arc over causing more damage. And lastly do not turn it on with the PSU not screwed down securely to the chassis, the decoader will be damaged, I have the 26" version in the identical cabinet as yours that I use as my main set in Norwich. It gives a lovely picture. I am using the later time base and IF panel. The later time base is much more stable and works ok with a VCR and the earlier IF board suffered from intacarrier sound buzz that drove me mad. The single chip early decoader though in my apinion produced the best picture. Good luck with restoration..
David

 
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Re: 1970 Bush CTV187CS

Post by stuie319 » Fri Aug 19, 2016 6:23 pm

CrustyTV wrote:
stuie319 wrote:A white 'acoustic deluxe' sleeps in my cellar, albeit in poor nick.

Stu

If you ever decide to move it on Stu there's a nice warm spot in the North. A set high on my list along with unicorn dust :qq1


Hi Chris, Not that I'm planning to, but if I decide to part with it, then I promise you've got 'first dibs'.
A bit o/t but this is the third of these sets I've seen in the flesh. The first was brought back by an installer and placed immediately in the tip pile. When I went to rescue it at lunch time the bin wagon had been :aaf This was the nicer of the three sets. The second set was one I was given by a customer during a new install, and it came straight home. It was 'cleared from storage' as I mentioned in another thread. The third set, here was an ebay acquisition a few years ago, typically it's the worst example of the three, cosmetically anyway.

Regards
Stu

 
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Re: 1970 Bush CTV187CS

Post by Colourstar » Sun Aug 21, 2016 9:19 am

With Brian R in attendance it's time to wake up the Bush. Well folks, first light..... then first darkness

The set powered up with the HT way up at 230v :ccf so that was turned down to a respectable level (200v). There was some snappy arcing to start with from where we could not see. The EHT cap was a bit loose so we thought it may be that.

The picture we got was as you see below; low gain, lack of height, convergence errors, no colour, brightness control not doing anything much.

It seemed to be settling down OK but on the next power-up there was a loud snap and a blue spark on the tube base (not near the spark gap though). This time we had sound but no raster appeared.

This colour lark is all too dramatic for me. I feel like I need a fag and a coffee (and I don't even smoke!) before returning to the calmer waters of nice friendly b&w sets that don't bite!

Steve
Attachments
DSCF5455.jpg
An image to treasure. It didn't stay long...

 
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Re: 1970 Bush CTV187CS

Post by PYE625 » Sun Aug 21, 2016 9:50 am

From what I remember from my youth....so a good 30 odd years when I last saw an A823, there is a pre-set on the frame board (towards the middle on the large board on the right) and I think it is a "set boost" ?......If turned too high, the EHT increases and the set trips out.

It could be that someone has randomly twiddled pots and pre-sets in the past.....in view of the fact the HT was too high to begin with.

Hopefully someone here will be able to enlighten further :qq1

 
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Re: 1970 Bush CTV187CS

Post by PYE625 » Sun Aug 21, 2016 9:59 am

Colourstar wrote:This colour lark is all too dramatic for me. I feel like I need a fag and a coffee (and I don't even smoke!) before returning to the calmer waters of nice friendly b&w sets that don't bite!

Steve


Relax Steve....You will be fine, I think you have landed in at the deep end so to speak, but take your time and don't be put off. :qq1

Have you got full service data for the set btw?

 
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Re: 1970 Bush CTV187CS

Post by CTV » Sun Aug 21, 2016 11:49 am

That's the trouble with the big power up on solid state sets, the three-legged beasties don't respond well to arc's and flashes. I had a whole decoder decimated due to that, hard lesson learned. Might have been wise to have had the tripler out to start with, still all part of the fun and games of CTV's. I'm sure Brian is well on the ball though and will see you through this.

A few checks to start with for a "No Raster" scenario.

  • Is 6R6 burning up? then check 6C6 .0047uF.
  • Is 6R9 is burning up? Check Tripler as it may be toast.
  • You have EHT but no raster so check 8R1 36R and 6R7 2.7K.
  • Check 6C13 for s/c ? .01uF, 6R7 will overheat as no A1 voltages.
  • Check 8R1 for o/c - this will give no voltage to the RGB emitter followers 3VT12, 3VT13, 3VT14
  • The demodulator and matrix I.C. could be faulty, destroyed by the arcing?

CRT voltages















PinElectrodeVoltage
1 Heater6.3V
2 K-Red 130V
3 Grid Red -3V
4 A1-Red 400-500V
5 A1-Green 400-500V
6 K-green 130V
7 Grid Green -3V
8 no-pin -
9A2 Focus 5-8kV
10 no-pin-
11 K-Blue 130V
12Grid Blue -3V
13 A1-Blue 400-500V
14Heaterchassis


Oh and SET EHT is on the power supply and is 8RV1

 
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Re: 1970 Bush CTV187CS

Post by PYE625 » Sun Aug 21, 2016 12:01 pm

PYE625 wrote: there is a pre-set on the frame board (towards the middle on the large board on the right) and I think it is a "set boost" ?......If turned too high, the EHT increases and the set trips out.




Had a look at the service data and I was thinking of RV1 "over volts protection" preset.

DON'T DO what I did 35 odd years ago and randomly adjust presets (not that you would of course).... the error of my youth. :ccb
Back then, A823's were plentiful and regular chuck-out's at my local TV shop.

 
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Re: 1970 Bush CTV187CS

Post by Focus 2 » Sun Aug 21, 2016 1:00 pm

The tripler input lead is soldered, not connected via tags. As the first power up seemed ok it appeared in order to carry out further tests. The HT was indeed high initially which was immediately tamed. All seemed happy despite the dreadful image on the screen. No signs of colour either, where does one start?

I might have known waking up a set after many years of inactivity component failures, notability transistors will start showing up...

My experience with the A823 series is limited to activity with one over 30 years ago. I was aware an arc from the PSU can destroy the decoder panel. On making cold checks the PSU was found to be in excellent condition.

Any A823 experts are very welcome to advise and even assist in repairs.

Cheers
Brian

 
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Re: 1970 Bush CTV187CS

Post by Focus 2 » Sun Aug 21, 2016 1:46 pm

Another very quick check confirms the absence of EHT. The CRT is prone to sparking over which could have ruined a transistor or two. This has certainly narrowed fault finding down. Possible suspect, the BD131 line driver transistor?

 
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Re: 1970 Bush CTV187CS

Post by slidertogrid » Sun Aug 21, 2016 3:09 pm

Its donkeys years since I worked on one of these but I remember the green flyback tuning capacitors caused trouble . Apart from sky high EHT they could also cause the transistors to fail. I think if one fails you get a large oversize dim picture. After replacing them there was a balancing procedure to go through but the ferrite core in the balancing coil was usually stuck. there was a sort of gluey grease on the core that stopped it moving on it's own accord but after a few years of heat cycling it became very stuck.
The thermistor would go dry on the PSU and flash over damaging the panel. Unfortunately it sits back to back with the decoder and sometimes the splat can flash over to the decoder print causing multiple faults.
Part of the decoder is on the IF panel ISTR so a no colour fault is not always on the decoder/RGB panel.
I have just found some A823 "droppers" (the double power resistor on the bottom chassis) so if you need a replacement let me know.
great thread ! following with interest!
:thumb
Rich.

 
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Re: 1970 Bush CTV187CS

Post by Colourstar » Sun Aug 21, 2016 9:15 pm

Sincere thanks to all for the help, suggestions and data. It's all greatly appreciated.

Thanks also to Brian who had the honour of the first switch-on! :ccf

In the next day or two when I have time I'll have a more relaxed analysis of the fault symptoms as they stand and decide on the next course of action. Although the EHT has vanished, the sound remains and the set hasn't blown any fuses so it can't be that mortally wounded. I'd like to know why it's producing a nasty spark and a loud 'snap' or two from the tube base at switch on. It does the nerves no good at all and it doesn't exactly provide a leisurely atmosphere in which to take voltage readings. The print on the tube base looks clean and well nigh perfect so I don't know what it's arcing from and to. It's well away from the spark gap, that much I think I did see. I don't really want to subject it to more switch-ons for repeat performances as it's probably not doing it any favours.

It's sure a tricky thing waking up a long-dormant solid state colour set. A nasty combination of high voltages and vulnerable semiconductors- and no gentle warm-up!

Steve

 
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Re: 1970 Bush CTV187CS

Post by neil29 » Sun Aug 21, 2016 9:34 pm

Luckily my CTV197C didn't really argue with me when I first switched on as all I had to do was adjust the preset on the power supply and it displayed a lovely black and white picture. as it has done since I bought it in 2007,i think?.


Cheers
Neil.

 
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Re: 1970 Bush CTV187CS

Post by CTV » Sun Aug 21, 2016 9:48 pm

Personally I always want to know what the EHT is running right at first switch on, this is why I ended up getting an in-line EHT meter like the BrandenBerg. Right from the word go you safely ascertain if your EHT is too high or low and if too high switch off before any problems. I've learnt on colour TV's to avoid the wand type meters, they have caused more problems with cracks spits and flashes especially if the EHT is way high. One thing I would have also done before switch on is have the EHT preset turned right down, you can always go up once you know things are ok and these sets run fine on 19-20kV. You might want to consider doing that. In fact I almost always run my sets down from the 24-25kV settling on around 21-22kV, it gives the triplers an easier time and we do need to start preserving these now.

None of the following is based on experience, it is however based on reading the service documents in the library. Hopefully it might be of use to you or jog others into debate and comment.

One thing I've read is you should check 6R11, if this fails the full unattenuated output of the tripler gets to the CRT and will cause the S.G to eventually explode and or burst into flames. Probably not related to your CRT PCB trouble but certainly something I would want to check to at least eliminate for peace of mind.

What is more likely and requires checking is there are 9 other spark gaps on the PCB other than the obvious biggy SG3 (rated 6-8kv) that need to be checked. Your violent cracking could be emanating from one or more of these. SG1,2,4,5,6,7,8,9 All are rated at 1.5kV. They should all be checked for condition and the gaps cleaned of any deposits.

Also there are two transistors on the CRT PCB 4VT1 and 4VT2, debatable whether they've survived the violence you describe in that area and are often discussed as being toast due to flash-overs. Failure of these results in dull picture and flyback lines.

The following also seems relevant to some of your initial "first light" symptoms and worth a check:-

If 4R3 goes open the beam limiter diode 4D2 is left without any forward bias and there will be a loss of brightness. For uncontrollable brightness also check the clamp/brightness pulse feed cap 8C11. Check 4R5/6/7 which can go open removing the appropriate first anode supply and subsequently colour loss. This is also true if 7C7/8/9 on the convergence panel go short or the first anode presets 7RV11/12/13 go open so check those too.

As you have EHT we know the tripler is OK so perhaps you should remove and test the BD131 line driver transistor. Again reading suggests this is also prone to going short which also blows the l.t fuse 8F1 has it? Sometimes it goes open, if that is the case you should check 5C25 and 5R35.

Don't forget the other checks I mentioned 7 posts back, I'll repeat here so you have them all in one place.

The few checks from my earlier post eliminate from suspicion for a "No Raster" scenario. Forget No.2 as we now know you have EHT.

  • Is 6R6 burning up? then check 6C6 .0047uF.
  • Is 6R9 is burning up? Check Tripler as it may be toast.
  • You have EHT but no raster so check 8R1 36R and 6R7 2.7K.
  • Check 6C13 for s/c ? .01uF, 6R7 will overheat as no A1 voltages.
  • Check 8R1 for o/c - this will give no voltage to the RGB emitter followers 3VT12, 3VT13, 3VT14
  • Check the demodulator and matrix I.C. it could be faulty, destroyed by the arcing? (see voltage table below)

A good few things to get on with and all easy checks there without needing to power up and soiling your undergarments :qq1

Brian said the HT was high and he adjusted it but did not state what all the other rails ( 18V,20V,25V, 200V) were like, are they OK. the 18V supply to the decoder and I/F especially interesting as the no colour could be related.


Anyway Steve had it worked out of the box so to speak what fun would that have been and what would you have learned? The greatest fun and education lies in a set that fights you and in the process so much is learned.

crt1.jpg

crt2.jpg

crt3.jpg

ic.jpg

 
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Re: 1970 Bush CTV187CS

Post by PYE625 » Sun Aug 21, 2016 9:51 pm

Colourstar wrote: I'd like to know why it's producing a nasty spark and a loud 'snap' or two from the tube base at switch on. It does the nerves no good at all and it doesn't exactly provide a leisurely atmosphere in which to take voltage readings.
Steve


It could be that the tube is slightly gassy and it will likely clear up during use, and warmth from the scan coils will help this.
The crt has a getter, rather similar to a valve.

The tip of disconnecting the tripler and allowing the set to warm through makes sense now.

 
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Re: 1970 Bush CTV187CS

Post by PYE625 » Sun Aug 21, 2016 9:57 pm

CrustyTV wrote:Anyway Steve had it worked out of the box so to speak what fun would that have been and what would you have learned? The greatest fun and education lies in a set that fights you and in the process so much is learned.


That is so true, and you begin to understand and learn all about the set and its circuitry over time.

 
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Re: 1970 Bush CTV187CS

Post by Focus 2 » Mon Aug 22, 2016 8:01 am

That's brilliant info Chris, very helpful. No I didn't get a chance to check other voltages, my main concern was the high HT which was adjusted to the correct 200V on initial tests.

Another thought is I've had problems with re-gunned tubes flashing over. I remember a 26" Invicta 697 flashing over resulting in an over bright picture with fly back lines. I immediately went for the BC108 blanking transistor on the CDA panel, restoring a normal picture on fitting a replacement.

Cheers
Brian

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