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Old 15th Jul 2010, 4:38 pm   #81
oldticktock
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Default Re: GEC BT1156 First Light & Vidor CN4216

Update:

Still measuring trying to find that elusive component which is giving me grief.

I cleaned the line hold, the vertical hold, and put in a new 30P4 and U191.

Still running with 7.6KV, 290V A1

Some voltage readings:-

R116 should be 120V but is 99V
C110 should be 72V but is 101V
R114 I think shoudl have 100V but on one side has -25V sometimes its - 1785mV on the other side of R114 nowt!
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Old 15th Jul 2010, 4:54 pm   #82
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Default Re: GEC BT1156 First Light & Vidor CN4216

Change R12. Also, if there are any resistors on the ends of the line hold control, change these too.

Then try it.

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Old 15th Jul 2010, 5:03 pm   #83
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Default Re: GEC BT1156 First Light & Vidor CN4216

You're very close Chris !
Did you do as post 80? What did you find ? Not just the resistors, the pot may have changed value.... they do sometimes.
Did you try a temporary silicon rectifier? If your HT is still low either the rectifier or the reservoir capacitor are suspect, the line frequency is now very close.
I see there are also some add-on dropper resistors... check they are the correct resistance values against the circuit.. It was very common for field service engineers to fit what they had in the van if that got the set working, rather than run the set in to the workshop or come back with correct parts.
HTH
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Old 15th Jul 2010, 5:15 pm   #84
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Default Re: GEC BT1156 First Light & Vidor CN4216

I have checked may resistors and posted results all were within 20%

Is R114 not odd? the service sheet states 100V ?

I did not add the IN4007 as per advice post #27

Teleman, Fenseh, Pete, Steve and Trevor, I will re-check back on all advice given so as not to have missed any of your valuable input or not to have followed advice.

cheers guys

My head hurts
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Old 15th Jul 2010, 5:31 pm   #85
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Default Re: GEC BT1156 First Light & Vidor CN4216

When your head hurts, stop. It's not a job. Honest guv.

Resistors go high in value, so if they have all gone high, that may be enough to put it out of range. Any that are more than 10% out, change, Check with the service sheet as to the correct value too,

Have a rest for now though, A tired worker makes mistakes.

R114 - That scope trace is 100v in total, The DC value will be slightly lower.

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Old 15th Jul 2010, 5:37 pm   #86
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Default Re: GEC BT1156 First Light & Vidor CN4216

Hi Chris.
That picture looks "nearly" locked so I would be looking at the line sync feed, the sync seperator is working as your frame is locked ok, so its the small value caps from the sync seperator to the line stage to check
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Old 15th Jul 2010, 5:45 pm   #87
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Default Re: GEC BT1156 First Light & Vidor CN4216

Steve is right, when your head's bursting it's time for a rest.

Not sure what you mean about R114. The service sheet shows a waveform that's 100v peak to peak when seen on a 'scope. It will be measured with the timebsase locked, which you haven't quite got yet. There will be a necative DC voltage here if you measure with a meter, but it won't be 100v. As the waveform is a high frequency one it can cause some meters to get upset, and then you can get all sorts of readings.
The makers usually specified what meter they used, and it was nearly always an AVO 7 or 8 depending on the vintage. That way, if the meter got upset or modified the voltage being measured due to its own resistance, you should still get the same reading as they did. It also gave a guide as to meter sensitivity required for those who had cheaper or just different instruments.

Quick question... is the line hold pot right at the end?
QQ 2 Is the picture stationary with those horizontal (i.e. zigzag) lines, or is it rolling sideways / vertically ?

Pete
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Old 15th Jul 2010, 5:53 pm   #88
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Default Re: GEC BT1156 First Light & Vidor CN4216

A1, Line hold is almost fully advanced just backed off a tad

A2, picture is unstable sometimes it's there, then its off again scrolls vertically.
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Old 15th Jul 2010, 6:35 pm   #89
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Default Re: GEC BT1156 First Light & Vidor CN4216

Lucky i'm stuborn and just can't give up

Not having enough experience yet, I don't know what that displacement at the top is

Now can I move onto finding out why the HT and EHT are low?

Chris
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Old 15th Jul 2010, 6:46 pm   #90
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Default Re: GEC BT1156 First Light & Vidor CN4216

Left running for a while it eventually deteriorates to this

I forgot to measure EHT & A1

I've switched off and will wait a while then measure both scenarios.
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Old 15th Jul 2010, 6:54 pm   #91
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Default Re: GEC BT1156 First Light & Vidor CN4216

Hi Chris
The line sync is weak so your not getting a good solid lock, I am just going out to the shed so I will have a gander at the circuit and give some pointers.
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Old 15th Jul 2010, 7:00 pm   #92
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Default Re: GEC BT1156 First Light & Vidor CN4216

You need to be able to go from below to above line freq by adjusting the hold control, in which case you would pass through a region of having a single "floating" picture, even if there's no sync. I'm sure you'd have told us if you can do this.
Watch what happens when you turn the line hold the last little bit.
If the slope of the bars becomes more nearly vertical it's a sign you are going in the right direction. The picture may then look less stable because at the moment it's trying to lock at line frequency minus an harmonic of frame frequency. (stationary display with a stable number of "black bars" per frame scan).
If you're still stumped when you've had a break and a recheck, could we have a look at the bit of circuit showing the line hold pot ?
Pete

PS Ah, I see you've progressed since I started typing ! What did you do ?

Last edited by DangerMan; 15th Jul 2010 at 7:02 pm. Reason: Added PS
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Old 15th Jul 2010, 7:06 pm   #93
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Default Re: GEC BT1156 First Light & Vidor CN4216

changed the Sync separator

Post #89 is how it starts after locking, post #90 is after about 10mins. I'm going to turn on again in a mo and measure the EHT and A1 when locked, then when it's gone all moody
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Old 15th Jul 2010, 7:21 pm   #94
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Default Re: GEC BT1156 First Light & Vidor CN4216

Ok turned on,

picture turns up locked and A1 is about 296.
Picture becomes better as time passes and A1 rises to 301V EHT is 8.2KV

after taking the photo the A1 reached 304.9V

I'm monitoring to see what happens

Edit:

Dunno what happened in pic 4 but, went round to look at screen and it was sorted.

monitoring continues.......... maybe it all goes pear shaped soon again.
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Old 15th Jul 2010, 7:43 pm   #95
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Default Re: GEC BT1156 First Light & Vidor CN4216

Hi Chris.
From the ERT sheet the parts to check are, Line osc, c109 200pf, r65 330k, r69 100k, r112 1k. sync seperator c90 3.9pf, c89 100pf. you have low width so also check these, the width control adjustment L25/26 linearity L27 also r113 180k, on the osc c110 0.01uf, r117 3.9k c111 0.01, line o/p valve screen feed and decoupler, the boost cap.
R114 680K G1 leak on the line o/p valve should be no more than 10% above value.
Try these for starters.
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Old 15th Jul 2010, 7:45 pm   #96
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Default Re: GEC BT1156 First Light & Vidor CN4216

Ok still stable...............

Now I think I will perhaps by-pass the old metal rectifier with a IN4007 and 2x220R (parallel) in series and see if the HT is improved.
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Old 15th Jul 2010, 7:50 pm   #97
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Default Re: GEC BT1156 First Light & Vidor CN4216

Chris.
In4007 is ok but 110 ohms as a limiter is way too high you need 22-47ohms but no higher you will land up wih less HT than you have now!
Mind this is a telly not a radio that needs less current

What is your present HT?
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Last edited by murphyv310; 15th Jul 2010 at 7:52 pm. Reason: added question
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Old 15th Jul 2010, 7:52 pm   #98
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Default Re: GEC BT1156 First Light & Vidor CN4216

Hi Trevor not talking about a limiter, I already have replaced the orginal duff EHT limiter which was a 5.1R (as per schematic) nearest I had was a 4.7R

I'm talking about the forward voltage resistor required when putting in a IN4007
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Old 15th Jul 2010, 7:55 pm   #99
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Default Re: GEC BT1156 First Light & Vidor CN4216

The correct terminology for the resistor in series with the IN4007 is a Surge Limiter, it does exactly as it says, so 22-47 ohms as I have said.

The 5.1 ohm you refer to is not an EHT limiter its only reduces the voltage to the EHT rectifiers heater, so they dont glow like a light bulb!
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Last edited by murphyv310; 15th Jul 2010 at 7:58 pm. Reason: Added Line
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Old 15th Jul 2010, 7:59 pm   #100
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Default Re: GEC BT1156 First Light & Vidor CN4216

Here's a pic of the EY51 tidied up Solder cups, and new resistor on the base of the EY51, I forgot to post this.

Before and after pics

Sorry Trevor was only repeating what I had heard & seen others call the in series resistor with silicon rectifiers and it's value, at least now I know better, thanks

Chris

Edit:

Well it's been almost 1 hour and the testcard is stable and bright.
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