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Old 9th Apr 2020, 7:50 pm   #41
Catkins
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Default Re: HMV 900 television restoration

Hi,

Earlier in this thread I posted about the Baird circuitry in the red, green and yellow circles on the circuit diagram shown in Photo 1. This post will finish off with the line timebase circuitry shown in the orange circle.

Like the circuitry in the yellow circle, this has been removed. Photo 2 shows where the Baird C11 capacitor would have been. The tags have solder on them but nothing else.

The C11 capacitor would have been connected to and from the standards switch, but those wires are missing. Presumably there was nothing else in the cableform which allowed it to be completely removed.

Photo 3 shows the cut off wire where the wire from the standards switch would have been connected to C10, R34 and T4.
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Old 9th Apr 2020, 8:21 pm   #42
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Default Re: HMV 900 television restoration

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Originally Posted by Heatercathodeshort View Post
Interesting to see the pots are manufactured in the U.S.A. I wonder if they originated from their RCA family? John.
They have no makers name on them, and the part number printed on them corresponds to the EMI parts list number. So I think it is more than likely they originated from RCA.
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Old 5th Oct 2020, 7:52 am   #43
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Default Re: HMV 900 television restoration

Hi,

It has been some while since I posted to this thread, and so I thought I'd post a quick update. In the meantime, I have finished the restoration of the electronics, put the television back together, and turned it on. What followed was a quite a large series of electrical faults until I was ready to connect up the CRT tube.

"First light" was achieved about two weeks ago. Photo 1 shows the very disappointing result. Obviously there was signal, line and frame scan but the performance of the tube was very poor. Picking myself off the floor, I had to remind myself there could be other causes other than a worn out low emission tube.

Photo 2 is the current status, after tracking down the faults which were causing the poor performance. I think it is a significant improvement

There is still at least a fault in sync separation, sync is currently on the edge and difficult to obtain, and the picture shows a strong tendency to "cog". This will likely be due to some out of spec resistances in that circuit.
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Old 5th Oct 2020, 8:04 am   #44
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Default Re: HMV 900 television restoration

Although rather dim the vision response in the first light photo looks really excellent.

Peter
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Old 5th Oct 2020, 8:37 am   #45
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Default Re: HMV 900 television restoration

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Although rather dim the vision response in the first light photo looks really excellent.

Peter
Yes, which meant in the early stages of finding the faults, it meant it was more likely to be a low emission tube .

As you'll know, there's things you can look for which can give an early indication of the four main causes, low emission, low EHT, poor HF response, low video signal (or drive as some call it).

The tests at that time were indeterminant because it was a combination of faults.

I intend to write up the fault finding there, and the previous work that got to that point.

I can start to do that now. The only real question in my mind, is whether I start at the very beginning, or when I got to the point of turning the set on. That's when it got more interesting.
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Old 5th Oct 2020, 9:32 am   #46
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Default Re: HMV 900 television restoration

Your second photo certainly shows that there's good life in the CRT and no obvious ion burn. If it is anything like mine I think you'll find that brightness and focus will improve with further hours of use.

Peter
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Old 8th Oct 2020, 3:28 am   #47
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Default Re: HMV 900 television restoration

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Originally Posted by peter_scott View Post
Your second photo certainly shows that there's good life in the CRT and no obvious ion burn. If it is anything like mine I think you'll find that brightness and focus will improve with further hours of use.

Peter
Yes, I hope that it will. It is also the case that the controls are adjusted to obtain sync, and not for the best picture
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Old 8th Oct 2020, 8:47 am   #48
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Default Re: Surviving Baird circuitry in a first generation TV set.

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Originally Posted by Catkins View Post
I intend to write up the fault finding there, and the previous work that got to that point.

I can start to do that now. The only real question in my mind, is whether I start at the very beginning, or when I got to the point of turning the set on. That's when it got more interesting.
To answer my own question, I have decided to start from the very beginning and on a new thread: https://www.vintage-radio.net/forum/...d.php?t=171831

This thread was supposed to be the restoration thread, but got immediately sidelined into the discussion of the surviving Baird circuitry. So this thread is really misnamed, and should be retitled to something like "Surviving Baird circuitry in a first generation set".

My problem is I think if I continued on this thread, many new-comers to the thread may be confused when the first restoration post in on page 3. Additionally non-experts may well be scared-off or turned-off by the first couple of pages dealing with obscure "expert level" discussion on the Baird circuitry, even before they get to the actual restoration posts.

I want the restoration thread to be appealing and accessible to non-experts, which is why I'm unhappy to piggy-back it on this thread, and so I have started a new thread.

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Old 8th Oct 2020, 9:06 am   #49
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Default Re: Surviving Baird circuitry in a first generation TV set.

Thread retitled and closed.
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