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July 20, 2017
2:48 pm
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Jayceebee
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acj1980 said Hmm i dont know what the word “bagded” means, but i think it maybe is fx jvc machine, but on the front of the machine there is another logo like Saba, Telefunken aso, am im right? 

You are correct Alex.

Thanks for the pictures as it answers many of my questions but also raises others.

The set has some differences to the sets produced here in the UK, the PSU appears to be completely different. It retains a thyristor for the main HT supply but the 18V supply to the decoder appears to be a transistor series regulator where UK models used a simple zener diode.

The tuner is indeed German as I suspected made by NSF but I notice that the antenna connections appear to be 300Ω twin flat cable rather than 75Ω coaxial cable used in the UK, is this still the same in Denmark today?

John.

July 20, 2017
7:20 pm
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acj1980
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Thanks John ;-), so far so good 😉 

Thanks for the information, maybe the changes is some kind of inprovement? this was made aronud 1970-71 or 72, in my television the date is september 1972, but it could also be a chance just for Denmark? :-O

 

The old flat antenna cable was just for few years we used those, from around mid 70ies allmost of the new television has the round plug like this , and we still use them 😉b872b5fe-2da1-4e0d-a6ed-228577971932.jpgImage Enlarger

I do some new seach and measuring on the HV part, after i put int the two transistors again, i notice then after few minuttes both gets very hot… as really hot :-(, and still only little voltage out from the HV transformer, i notice the signal to booth tansistors basis and there was a large difference in signal amplitude, is that what i can espect to measure there? (se the pictures).

Another thing is the horizontal signal from the line oszillator, it´s more square signal than ordinary line signal for HV transformers, it dosen´t seems to be right , but still i dont know how it look like for this chassis :-O

 

left BU transistor

right BU transistor

Hor Osc, at 15.5khz

 

Best regards 

Alex 😉

July 20, 2017
7:52 pm
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nuvistor
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The drive to the two BU105 transistors needs to be balanced by adjusting inductors. I think there are resistors in the base circuit than go high in value, this increases the dissipation in the transistor.

Just looked at the waveforms in your post, they do look very wrong.

Frank

July 20, 2017
8:00 pm
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acj1980
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nuvistor said
The drive to the two BU105 transistors needs to be balanced by adjusting inductors. I think there are resistors in the base circuit than go high in value, this increases the dissipation in the transistor.

Just looked at the waveforms in your post, they do look very wrong.  

Thanks Frank.

 

Yes i knew it was wrong, but the signal from the hor. osc is not right i guess, i change the resistors between B-E, it was 10 R, but the one was 17 ohm.

 

About inductors, do you mean those to small near the BU transistors?

 

Alex 😉 

July 20, 2017
8:12 pm
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nuvistor
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I haven’t got a circuit to hand and cannot remeber just where the inductors are, it’s 40 years since I last saw one. I will have a look around see what I can find.

Chris posted some links well worth a read, this is one of them, just be aware that your set could have some design changes to the UK sets.

https://www.radios-tv.co.uk/rbm-a823/

Frank

July 20, 2017
8:34 pm
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Jayceebee
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It’s not really possible to measure the base of the upper transistor 6VT1 if your oscilloscope earth probe is grounded. You have to remember that two transistors are stacked on top of each other as a single BU105 couldn’t cope with the power required and peak inverse voltage (PIV) in those days. Are the transistors overheating with the tripler disconnected?

6C5 and 6C6 were prone to failure in very early models but the later sets were fitted with green Plessey types which were much improved. I might be wrong but I seem to remember the originals may have been polystyrene, I’m sure they looked like large Sufflex types with a blue wrapping?

A823.pngImage Enlarger

A823-osc.pngImage Enlarger

John.

July 20, 2017
11:05 pm
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Chris
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nuvistor said
I haven’t got a circuit to hand and cannot remember just where the inductors are, it’s 40 years since I last saw one.

This recovered from my spares should jog your memory

a823-2.jpgImage Enlarger

July 21, 2017
12:40 am
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acj1980
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Thanx guys for information, and thanks to you Jaycebee for showing the HV circuit, i can see that my HV is like yours Chris, exept those two green plessey caps, i dont think they are good anymore, so far so good, so there is only the signal and signal amplitude problem, maybe it could be the hor. osc the problem is?.

I will take a look on it tomorrow

 

Alex 😉

July 21, 2017
10:57 pm
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acj1980
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i wish i have some scope pictures from the schematic of the horizontal oscillator, measured from the connectores to the 6L1 transformer who feed both the BU transistors

July 21, 2017
11:20 pm
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Chris
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You’re almost at Technical Library level access (If you hover your mouse over your level indicator, you will see its at level 3/720), in the meantime this will help you to keep going.

Click once, then click again to get fully expanded view.

a823-1.pngImage Enlarger

a823-2.pngImage Enlarger

July 21, 2017
11:35 pm
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acj1980
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Chris said
You’re almost at Technical Library level access (If you hover your mouse over your level indicator, you will see its at level 3/720), in the meantime this will help you to keep going.

Click once, then click again to get fully expanded view.

a823-1.pngImage Enlarger

a823-2.pngImage Enlarger
  

Thanks Chris you are great 🙂 , i will take a look on it, 🙂 thanks again
 

July 23, 2017
5:53 pm
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acj1980
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So far so good, i just found out i have make an mistake, and replaced to wrong capacitors (6c5 &6c6) they have to be 4.7nF mine was 47nF, so that´s why nothing really happens :-).

So now the EHT works, som next problem is how i can get the colour on the screen, i notice that the Green gun was down on this picture, the fault was the transistor VT13 (bf194) on the scematic it is a BF194, but in this TV it´s a BC172b, i replaced it and now all guns are driving, but still no colour, nomatter what im doing no colour, i have an other  decoder component prefix no3 circuitboard ant try this, no colour 

20170723_180701Image Enlarger

 

Alex 😉

July 23, 2017
6:05 pm
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Chris
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So I take it you now have green drive and the picture shown above is prior to you restoring green to working operation? I further take it you have a reasonable looking grey-scaled test card?

I would disable the colour killer (shorting 3TP11 to 3TP14) on the decoder to see what the actual colour fault is, could be something very simple like the reference osc needs a tweak or the crystal replacing.  The A823 guide here from page four onward has superb advice on diagnosing decoder faults on the RBM A823.

Common faults start on page 6 of the pdf( 32 of doc), start with checking the 18V supply (3TP11) is there, they state the decoder is one of the most reliable and the i.c. or an electrolytic are the prime candidates. Not forgetting some components on the i.f panel for chrominance, anyway loads of useful info that will get you sorted.

August 14, 2017
9:03 pm
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acj1980
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Well it´s being a while since i wrote inhere, i am back in school for a short school  and then back again, status on my Arena is i got colour on the screen but it wasn´t clean colour, so far so good, i notice the screen was a little bit shrinked so i adjust the EHT for largere picture and then….. black screen and absolutely NO EHT :-O, what in the H… goes wrong now? since the EHT dosent work? i can feel the heat from BU transistors, after a short tine the TV is turned on,  

 

Alex 😉 

August 14, 2017
9:23 pm
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PYE625
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Be careful Alex, don’t increase it beyond the correct limits  bang_gif

You may have caused the over-voltage protection to activate.

Forgive me if I state the obvious, but please  carefully read the manual and data.  read04

Andrew.                                                                                   

                         

August 14, 2017
9:42 pm
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Chris
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acj1980 said
[..]  black screen and absolutely NO EHT :-O, what in the H… goes wrong now? since the EHT dosent work? i can feel the heat from BU transistors, after a short tine the TV is turned on,  

I suspect you’ve read about this but if not check if the line output transistors have died, if they have then the most likely cause is lack of balance between them. Is 8F3 blown? Where 6R6 is of the fusible type check to see if its gone o/c. Also check the flyback tuning caps 6C5 abd 6C6. If the line output transistors have gone and you replace them they will need to be rebalanced. This is critical as if they are not timed to be turned off at the same time, one transistor will take the full flyback pulse.

Good thing is, now you have library access you can download the full RBM manufacturers service manual. grin_gif

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