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CTV Decca CS2230 Bradford

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slidertogrid
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This set came my way a while back, it has been languishing in my spare room since. I was pleased to have this particular model as it is exactly the model my parents rented new from Granada for a year before buying the Marconi 8500 which I still have.

I heaved the set onto the bench, all of these old colour sets seem a lot heavier now than I remember ! The PCF802 and PCF80 were missing so after fitting replacements I powered the set up gently with the heater chain open to prevent it trying to work, and after I had satisfied myself that the HT smoother was OK I reconnected the heaters and powered up leaving the Variac at 200V. 

There was a bit of a screech from somewhere and then I noticed the PL509 starting to glow. I found there was virtually no line drive. I found three electrolytic capacitors way out of value and a Suflex that was suspect. After replacing those and refitting the panel I turned the mains up to 240V and checked the DC voltages on the PCF802 anode was about right. The drive was better but still low. I tried another new PCF802 and suddenly I had plenty of drive however it leapt about all over the place when the valve was touched. Cleaning the valve pins and holder seems to have settled that down so the PL509 top cap was refitted and the input to the tripler re-soldered.

Screen illumination at last, low height and really just a blue blur. It didn't take long to find the blue screen someone had replaced the 10k badly and it was o/c. Tacking in a replacement and setting the A1 controls has given me a nice (ish) snowy raster. the PL508 was very slow warming replacing that has given me full picture height.

The tuner is seized so I

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can't tune the buttons but rocking the tuner bar back and forth gives me some very snowy horizontal lines and a faint buzz on sound (the volume is very low) the tube isn't bad and seems to be getting better already. Tomorrow I will remove the tuner and see why I have very low gain and see if the mech can be persuaded to move....

Wish me luck !   

 
Posted : 04/02/2023 9:20 pm
LSmith, Lloyd, Jayceebee and 1 people reacted
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Jayceebee
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Had a rather nasty incident with that particular model very early in my career. A relative asked me to look at theirs which was dead due to a blown mains fuse. A replacement was fitted as it looked like it had just parted, I stuck my head virtually inside the set and felt around the front for the on/off switch. They saw you live and learn and certainly learned never to do that again, as I rotated the switch I was blinded by a huge flash deafened by a mighty bang and hit in the face with glass from the fuse and bits of a Dubillier mains filter capacitor. Thankfully I've worn spectacles all my life and they probably saved damage to my eyes from the mini explosion.

Good luck with it.

John.

 
Posted : 04/02/2023 10:14 pm
slidertogrid
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Ouch! I must admit I snipped the capacitor before powering up it's a grey plastic one in this set I don't know what make I will get a better look tomorrow once I have got the front panel out to hopefully sort the tuner.  

When I first started working for myself (1981) these sets were being disposed of by the ex-rental outlets. You could buy a "worker" or "off the pile", the off the pile sets were the ones with flat tubes that had been filled with faulty panels. I found they were the best value because you could fit a regun tube and repair them fairly easily. The workers were usually boosted and often bodged. I did have one decoder panel with no colour though that I never did solve. I didn't have a 'scope at the time and faulty second hand panels were available cheap from the disposal places from smashed up scrap sets. I soon had a set of boards on the van and a repair jig in the workshop made up of a chassis and fairly flat tube with 8V on the heaters! They made good banger rentals and I never had to haul one back for repair! 

 
Posted : 04/02/2023 10:28 pm
slidertogrid
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A little bit more progress today. I removed the tuner I found the PCB on the back had become unsoldered from the legs of the tuner and a "tropical fish" capacitor had cracked on both ends as soon as I touched it it fell off.

Re-soldering the panel to the lead-outs from the tuner and tacking in a replacement capacitor made absolutely no difference. All I could get was faint disturbance on the screen at one tuning point. The sound then spluttered and popped so I replaced the PCL82 this restored normal volume but only a white noise no audio 'when tuned in'.

I have a new Telefunken NSF tuner in stock bought some time ago when (I think) Mike Cathovisor had a few for sale. I knew it would come in handy! I bought it as a spare for my Keracolour, another set I need to fix!  Anyway with that tuner connected up I have sound and even more disturbance on screen but nothing resembling a picture.

Rocking the R.F out plug from the tuner on the I.F panel produces flashes and brief unlocked video so I think the next job will be to remove the panel and investigate the print. This set is starting to look like an 'untested off the pile' set with faults on every board! I wonder if there will be any colour?!

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The mains filter cap is a grey Plessey but is probably best replaced.

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Posted : 05/02/2023 1:37 pm
Cathovisor
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Posted by: @slidertogrid

I have a new Telefunken NSF tuner in stock bought some time ago when (I think) Mike Cathovisor had a few for sale. I knew it would come in handy!

Yeah, that was me... 😀 

 
Posted : 05/02/2023 2:34 pm
slidertogrid
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It's been an interesting few hours.... I found the virtually no signal problem on the IF board was due to the shield on the back of the panel shorting out due to being loose there was also some suspect dry joints. Then I had a bit of picture with no sync very low contrast. I then discovered the contrast control was open circuit with a broken track. The colour pot is the same I think they have been clouted probably when the set was dumped. I have bodged the contrast pot temporally and wired a pre-set pot in place of the colour control. 

We Have a picture! After a bit of adjustment not too bad a picture! The picture shift was miles out as was the frame linearity and brightness range so either this set has been twiddled or has been used as a panel donor at some point...

No Colour and still lashed up on the replacement tuner next plan is to sort the or a tuner, find some replacement control pots and get the front panels back in.

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Then see why I have no colour... I hate decoder faults!

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Posted : 05/02/2023 6:26 pm
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slidertogrid
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Can anyone tell me how to override the colour killer please? Do I link TP205 and TP206? I have a vague memory... But I dare not risk it in case I am wrong. I have a Telefunken service manual rather than a Decca one and it is comprehensive but doesn't mention how to do it. The decoder diagram shows that these two test points if linked will connect the emitter and collector of the colour killer Transistor TR208 so I think that is what I need to do... I would just like to confirm that is right before I do any damage! 

 
Posted : 06/02/2023 6:49 pm
crustytv
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Posted by: @slidertogrid

Can anyone tell me how to override the colour killer please? Do I link TP205 and TP206? I have a vague memory... But I dare not risk it in case I am wrong.

Rich, there is nothing wrong with your memory, that is exactly how you defeat the CK on a series 30 Bradford. It was the series 10 that differed. 👍 

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Posted : 06/02/2023 6:59 pm
slidertogrid
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Many thanks Chris,  I had a memory that the two test points were the same TP number that's what confused me! Not that it takes much these days! 😀  

 
Posted : 06/02/2023 7:22 pm
slidertogrid
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Overriding the colour killer has produced unlocked colour running through which can be altered with the reference oscillator potentiometer but won't lock. (Stronger colour than appears in the picture) I have tested TR212, BC148 which tested OK but to be sure I have replaced it, lock-fits being what they are!  No change.

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Next on the check list is the two 1N4148 diodes D205 /206. Time for tea first though! 

 
Posted : 11/02/2023 4:23 pm
slidertogrid
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Time to ask for Help! I checked the diodes 1N4148 they seemed ok but to be sure I fitted two new ones. Then the luminance vanished! That was easy to find the luma delay line was very dry jointed. Panic over! R272 had a dry joint and when I re-soldered it the end fell off the end cap had split as these do. I replaced the resistor and the symptoms seem to have changed slightly, the colour running through seems now to be orange and the 'bars' are slightly wider. ??

Could the Varicap diode be the problem? It's a BA102 I haven't got one and don't think I can test it. Am I looking in the right area?

Rich

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Posted : 11/02/2023 7:06 pm
crustytv
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This should be of some use.

dec30

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Posted : 11/02/2023 7:53 pm
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Jayceebee
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Posted by: @slidertogrid

Then see why I have no colour... I hate decoder faults!

You and me too, especially on video recorders. 

Posted by: @slidertogrid

 the colour running through seems now to be orange and the 'bars' are slightly wider. ??

Could the Varicap diode be the problem? It's a BA102 I haven't got one and don't think I can test it. Am I looking in the right area? 

The wider the bars the closer you are to 4.433MHz, can you get the colours to run through or virtually lock? If so then the varicap is unlikely to be faulty as if it was I suspect the reference oscillator would be way off frequency with lots of colour bands. Do you have a pattern generator? If so set it to red and look to see if the red unlocked red colour is OK at the edges.

Do you have bags of chroma with the colour control at max? Check your levels going into the decoder. If there is a fault in the ACC circuit you may not have enough chroma burst for the 4.433MHz reference oscillator to lock on to. Time to get the scope out.

John.

 
Posted : 11/02/2023 8:04 pm
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slidertogrid
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Many thanks both for the replies, I will have another look tomorrow once my errands have been done! Rich

 
Posted : 11/02/2023 9:23 pm
slidertogrid
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I have had an hour or so on the set today. I have checked the suggestions in the fault guide that Chris posted, the resistors all checked a little high as these old ones often do. I have replaced a couple that were out of tolerance. 
The colour bands can be made to run through and stop stationary but no colour lock. The two photos show colour bars and red raster. If the control is set to get the colour bands stationary on the bars it has to be reset to get the bands stationary on the red raster and vice-versa?

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I think John may be right in so much as the colour is turned right up and the chroma is not excessive. The colour control will turn the colour level up and down so it is working.

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Posted : 12/02/2023 5:57 pm
Jayceebee
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@slidertogrid Looking at those last pictures I can't be sure but it looks like there is also no PAL switch action giving blinds on the unlocked colours. Might be worthwhile seeing if you have a 7.8KHz waveform present at TR209 collector, also three electrolytics C230,2,4 in that stage and colour killer which would be worth a look.

If anyone else needs it the Decca 30 decoder circuit is on P42 of the PDF here

John.

 
Posted : 12/02/2023 8:46 pm
slidertogrid
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Thanks for the help John, I have checked the capacitors, they were all reading high value so I have replaced them. (I had already replaced C232).  The waveform on TP207 looks right but there seems to be a little instability on it, or this could just be me! I didn't have much time today but I am hoping to get another look tomorrow. I am very thankful that decoder faults on these early sets back in the day were uncommon! Back then I worked for a PYE dealer so most of the decoder faults were on the Pye hybrid chassis which I eventually found my way around...ish! 

As far as colour faults on Video recorders, luckily, I employed I video engineer so I only had to cover for him when on holiday etc. Any Colour faults or any other problems I couldn't solve awaited his return! There were usually a few.... 😀  

 
Posted : 13/02/2023 7:38 pm
slidertogrid
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This is the waveform on the collector of TR209 (TP207) . I found a couple of resistors in the same area 50% high but replacing them has made no difference.  There is no colour unless the colour killer is overridden with the potentiometer at it's original setting, but unlocked colour can be made to appear with the colour killer not overridden if the pot is adjusted?

Could the MC1327 be at fault?

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Posted : 14/02/2023 2:43 pm
Jayceebee
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I would expect to see a nice large 7.8KHz sinewave at TP207 but without knowing the 'scope settings I can't tell if it's correct. I don't think the IC is at fault with the symptoms you have but it might be possible. The lack of bags of unlocked colour still concerns me, the ACC stages and chroma amp TR205/6 are troublesome BF197s so check voltages around them. Quick and dirty test is to measure between base and emitter for anything wide of 0.7V.

John.

 
Posted : 14/02/2023 7:37 pm
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Till Eulenspiegel
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Re. the oscilloscope trace showing the 7.8Khz sine wave. What was the volts/division setting? The 9volts peak to peak waveform will be clipped to create a square wave signal for ident and R - Y switching. The circuit designer chose the negative part of the sine wave to supply the voltage to activate the colour killer.  So the positive part of the waveform does the actual ident function. 

Till Eulenspiegel.

 
Posted : 14/02/2023 9:00 pm
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