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Old 10th Nov 2017, 12:54 am   #1
Seidways
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Default ALBA T14 - Grey Raster with Retrace Lines

Hi everyone,

I recently bought an ALBA T14 Television set (believe it's early 70's vintage) as a restoration project. I powered up the set awhile back only to get a grey raster with retrace lines (no white noise).

I've changed out the majority of the electrolytic capacitors in hope this may solve the problem but it still remains. Was thinking possibly screen voltage set too high? I'm personally more familiar with working on more modern CRT televisions and computer monitors so I was rather puzzled not to find a G2 adjustment on the flyback or anywhere else around the chassis for that matter. Was also thinking a possible G1 short could be the culprit but I tested the tube on my B&K 470 and it tested no shorts.

Anyone knows what might be causing this issue? Thanks
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Old 10th Nov 2017, 6:30 am   #2
Steve_P
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Default Re: ALBA T14 - Grey Raster with Retrace Lines

This is a BRC190 in disguise,

Have you got a test meter and are you aware of the voltages in a TV set? I notice that this is your first posting here.

The IF on these gives trouble - VT4 is a favourite. Fit a BF194. I have not got my hands on a Manual but the components are all printed on the panel.

Cheers,

Steve P,
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Old 10th Nov 2017, 7:34 am   #3
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Default Re: ALBA T14 - Grey Raster with Retrace Lines

The service manual and Les Lawry-Johns service articles are available in this thread.

https://www.vintage-radio.net/forum/...ad.php?t=35588

Keith
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Old 10th Nov 2017, 4:21 pm   #4
Seidways
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Default Re: ALBA T14 - Grey Raster with Retrace Lines

Thanks Keith for linking the service data. Will take Steve's advice and attempt to replace the transistor and see if this fixes the issue. Thank you both for the support!
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Old 17th Nov 2017, 5:59 pm   #5
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Default Re: ALBA T14 - Grey Raster with Retrace Lines

Follow Up: I've replaced VT4 with a new BF194 and still the issue with the retrace lines remains.

I've measured the voltage of the transistor with my DMM, 10.6v on the Collector and 0.7v on the Base. This appears to differ slightly from the schematic (12v Collector, 0.6v Base) but not enough to make me think this would cause an issue.

Any further feedback on where to go next would be greatly appreciated
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Old 17th Nov 2017, 10:28 pm   #6
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Default Re: ALBA T14 - Grey Raster with Retrace Lines

Hi, the fact that you have retrace (flyback) lines on the screen suggests to me something wrong in the video output stage or the biasing of the CRT, does the brightness control have any effect and can any audio even white noise be heard?

My first suggestions would be to ensure that the video output HT supply 95v is present at the cathode of W14 then check the voltages on VT9. It would be a good idea to replace C111 in the 95v supply if you haven't already. A suitable replacement for VT9 if it appears faulty would be a BF336 or BF337.

Good luck.
John.

Last edited by jayceebee; 17th Nov 2017 at 10:50 pm. Reason: more info
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Old 18th Nov 2017, 9:22 am   #7
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Default Re: ALBA T14 - Grey Raster with Retrace Lines

I think it is just possible that you haven't got a fault at all.

You will need a signal source such as Aurora, adjust the set if necessary for a locked picture and then see if the flyback lines are still there.

If you still have flyback lines with the time-bases locked follow the blanking pulses from the time-bases to the grid of the CRT with an oscilloscope.
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Old 18th Nov 2017, 4:47 pm   #8
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Default Re: ALBA T14 - Grey Raster with Retrace Lines

Hi John,

Yes, both the Brightness and Volume controls appear to work as intended. I can hear static noise from the speaker.

I went about checking the voltages you'd mentioned. The cathode of W14 measured 81.5v (seemingly a bit low), going to measure VT9 I got 0 volts on both the base & emitter but 82.5v on the collector, the schematic specifies 45v so no doubt that transistor is dead.

I found probing the voltage on that transistor also has seemingly screwed up the brightness control which would previously completely darken the screen at the lowest value but now only dims the screen and seems to now have less of a brightness range, perhaps I've shorted something? D:

As for C111, I'll need to order a replacement 1uf 350v cap to swap that one out. I'll also go about changing VT9.

Also as Colin made mention, I did try to tune in an RF signal from my VCR to no success. It was my understanding this set is 625 Lines and that it can accept a standard PAL signal and not need conversion to a 405 line signal for the TV to accept it. Am I wrong in this regard?

Thanks everyone for your continued support
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Old 18th Nov 2017, 6:22 pm   #9
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Default Re: ALBA T14 - Grey Raster with Retrace Lines

It won't be from an Aurora as it's single standard UHF 625 lines. The RF output from a Sky box would do nicely...
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Old 18th Nov 2017, 7:26 pm   #10
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Default Re: ALBA T14 - Grey Raster with Retrace Lines

I had assumed (wrongly apparently) that the Aurora has a 625 mode. Perhaps that will come in a later model, 625 analog sets are becoming vintage now.
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Old 18th Nov 2017, 11:12 pm   #11
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Default Re: ALBA T14 - Grey Raster with Retrace Lines

Ok, so no volts on the base of VT9 would lead me to suspect that VT6 requires some investigation, I would be surprised if the b-e junction of VT9 was s/c. The base bias for VT9 comes from the emitter of VT6 and although the manual shows it as TVT5 it will almost certainly be a BF197.

It would also be a good idea to check the voltages on VT5 which again will be a BF197, a good transistor should have a voltage of around 0.7v measured between the base and emitter, these Mullard transistors are known as a lockfits and were very troublesome. The TVT5 type referred to in the manual is something Thorn used for a group of transistor types which were deemed suitable for use in this position. I don't recall all of the types that were listed under TVT5 but a BF199 could be used although BF197s gave the best performance.

John.
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Old 19th Nov 2017, 8:55 am   #12
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Default Re: ALBA T14 - Grey Raster with Retrace Lines

See Post#17 and on....here:

http://vintage-radio.net/forum/showthread.php?t=133024

Lawrence.
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Old 19th Nov 2017, 9:33 am   #13
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Default Re: ALBA T14 - Grey Raster with Retrace Lines

You mention that you get 'static' from the loudspeaker. With the circuit working correctly you should get a roar of hiss.

Sound take off is from the collector of VT5 the final if amplifier.

I would take a look around VT1 the AGC amp transistor and the preset contrast pot R2 4K7.

I presume you have eliminated VT2/3/4. John.
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