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 Post subject: Sony Micro TV with no audio
PostPosted: Oct Sun 11, 2020 6:57 pm 
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Joined: Feb Mon 17, 2020 5:23 am
Posts: 21
Location: Barron Co., WIS.
Hi everybody! I recently bought a 1967 Sony TV-500U off of eBay for super cheap in untested condition. When I tested it out everything worked great, the CRT was decently sharp and the audio was good. But after I did the very suggested recap of it the only audio that was there was a slight hum, plus the normal audio was even quieter that that, and that was with headphones on! My hearing is pretty good since I'm not even 20 yet, so you can imagine how quiet it was. I don't know a ton on the topic of solid state electronics so if it seems like a transistor or transformer error let me know on that. I also thought it could be an issue with a capacitor going open? I didnt replace all of the electrolytics so maybe the heat got to them? I looked for cold joints and I couldn't find any with a quick search. Has anyone else had this issue? I'd really like to get this fixed and working because I think it's a pretty cool little TV set! Thanks for your help! :D


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 Post subject: Re: Sony Micro TV with no audio
PostPosted: Oct Mon 12, 2020 12:43 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 1032
Location: Belrose, NSW, Australia
You broke the first rule of engineering:

IF IT AIN'T BROKE DON'T FIX IT!

You got bad advice I'm afraid. I have one of these TVs in 100% original condition and it works just fine. There is no reason to change caps in a solid state device as a prophylactic measure, as there is with wax paper caps in older tube devices. Japanese electros are generally good, even ones that old. And they will get better with use.

Did you say you used a solder gun? Very bad idea on solid state gear. Circulating earth currents can damage solid state devices. I hope it's not that.

You will need to inject an audio signal at the volume control and see if the fault is in the sound IF or the audio amplifier. If no audio when you do this, that narrows down the area to make it easier to find where you made a mistake when fitting caps.

Do you have the schematic?

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Wax, paper, bitumen, cotton, high voltages - what could possibly go wrong?


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 Post subject: Re: Sony Micro TV with no audio
PostPosted: Oct Mon 12, 2020 6:56 am 
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Joined: Apr Sun 08, 2007 6:47 am
Posts: 4182
Location: British Columbia
I wouldn't say that Japanese electrolytics are usually good, Sanyo/Channel master transistor sets are often found with bad caps in them, those hideous plastic shell ones anyhow. Whilst it's true that the work done to it likely caused a snag that does not mean it was not worthwhile changing the orginal electrolytics, Sony's used bucket loads of grey Elna caps which do NOT have the best reputation for reliability, especially 53 years later. The good think about the Sony mini TVs from that era is that the boards are socketed into an edge connector so you can remove them for inspection without having to unsolder a dozen wires. I would look into whether the edge connector, or the P.C board traces that plug into it, are dirty, or loose, as well as inspecting the wiring going to the socket, and whatever new solder joints were made. It may even be something simple like the speaker is disconnected.
Regards
Arran


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 Post subject: Re: Sony Micro TV with no audio
PostPosted: Oct Mon 12, 2020 10:37 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 1032
Location: Belrose, NSW, Australia
My point was, WHY change all the electros when the TV is working? It makes NO sense at all. All you've got now is a broken TV.

Sony generally used high quality parts and conservative design so even if the ESR has risen on some electros there's enough reserve in the design to allow it to operate.

The idea seems to have got around that if you just change all the caps you'll fix it. That may be true occasionally with tube stuff and paper caps (which should always be changed) but is not a given for solid state gear. and electrolytics. I have a mid 50's Australian Philips transistor radio that gets used daily. Apart from the battery it is 100% original and a strong performer. It's fitted with 1950s yellow Australian Ducon electros. I would generally regard Japanese electros as better.

I agree with you about those plastic cased electros.

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Wax, paper, bitumen, cotton, high voltages - what could possibly go wrong?


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 Post subject: Re: Sony Micro TV with no audio
PostPosted: Oct Mon 12, 2020 11:35 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 17961
Location: Utica, NY 13502 (USA)
Quote:
I didnt replace all of the electrolytics
Of the ones that you did replace, did you observe their polarity and replace correctly?

Dave


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 Post subject: Re: Sony Micro TV with no audio
PostPosted: Oct Fri 16, 2020 7:58 am 
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Joined: Jan Thu 16, 2020 12:29 am
Posts: 768
irob2345 wrote:
My point was, WHY change all the electros when the TV is working? It makes NO sense at all. All you've got now is a broken TV.

Sony generally used high quality parts and conservative design so even if the ESR has risen on some electros there's enough reserve in the design to allow it to operate.

The idea seems to have got around that if you just change all the caps you'll fix it.


It is surprising how many people blindly follow advice about recapping apparatus, where the procedure is not indicated, for particular items. Probably the people who follow the advice are less experienced in electronics diagnostic skills, possibly even practical skills & desoldering techniques or realize that the vintage phenolic boards in these sets are fragile & heat sensitive, as are the germanium RF transistors. Without skill & experience a lot of damage gets done. Yet those with the knowledge and skill, like yourself, don't fall for the Global Recap advice and assess faults on a case by case basis.

It is sad really, because we are seeing a lot of good vintage gear get damaged and ruined because of the bad advice and the willingness to follow it.


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 Post subject: Re: Sony Micro TV with no audio
PostPosted: Oct Fri 16, 2020 11:39 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2096
Location: Waukegan, IL
I have a older sony micro tv. Before i replaced the electrolytics on the deflection board i had a small picture and some hum bars. After a deflection board recap, it works. There were quite a few Elna caps that had electrolyte leaking out the bottoms.

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Tony Pignaloni


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 Post subject: Re: Sony Micro TV with no audio
PostPosted: Oct Sat 17, 2020 10:55 am 
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Joined: Jan Thu 16, 2020 12:29 am
Posts: 768
Well, maybe the responses were a little harsh.

A better proposition might have been to pose the question :

How do I know when the electrolytic capacitors in my vintage transistor TV need replacing ?

Luckily there is a sensible answer. Usually, in any particular TV, the capacitors are of the same brand and age. It could be a reasonable assumption that if most of them are ok, probably the other will be.

Firstly, if the power supply is generally good, without gross ripple voltages getting into the audio & video, you can assume the power supply electrolytics are at least reasonable.

What about the rest of them ?

Unlike other apparatus (radios & amplifiers), the vintage transistor TV gives you an amazing insight into the performance of its electrolytic capacitors. This is because of the vertical deflection amplifier in the TV and the fact that the result of capacitor degradation it is plainly displayed in front of you on the CRT face, somewhat analogous to an oscilloscope recording.

If there is anything wrong with the electrolyic capacitors, specifically coupling capacitors in the vertical deflection amplifier, say if they have lost uF value, or have become high ESR, it is immediately apparent from inspecting the vertical linearity that something is wrong. As the capacitors age (uF value down & ESR up) it results in a loss of LF response and this results in compression of the scanning raster toward the bottom of the scan (line crowding) which is not corrected by the vertical linearity control range. You would never pick this defect if the defective capacitors were just say in an audio circuit, it requires a visual representation.

So the advice is; if the vertical linearity is good in the vintage transistor TV, then likely all of the electrolytic capacitors are ok and do not definitely require replacing. If the vertical linearity is off, and not correctable, this means the electrolytic caps in the vertical stages are likely becoming aged and degraded, and possibly they are also doing that elsewhere, but without obvious effects.


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 Post subject: Re: Sony Micro TV with no audio
PostPosted: Oct Sat 17, 2020 3:07 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 17961
Location: Utica, NY 13502 (USA)
In my experience, the low-value coupling caps in solid state audio circuits are often first to go open regardless of manufacturer or brand.

Dave


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 Post subject: Re: Sony Micro TV with no audio
PostPosted: Oct Sat 17, 2020 9:46 pm 
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Joined: Jan Thu 16, 2020 12:29 am
Posts: 768
Dave Doughty wrote:
In my experience, the low-value coupling caps in solid state audio circuits are often first to go open regardless of manufacturer or brand.

Dave


Yes, but say if a coupling capacitor was down to half its original uF value, you would not detect that in an audio circuit unless you did a frequency sweep and found the response at the low end was falling away. Unless the radio was connected to a Hi-Fi speaker (not its own, unless say it was a Hacker Sovereign) and you had golden ears.

In a transistor TV, especially in the vertical deflection circuits, any loss of the LF response is immediately apparent by looking at the scanning raster.In a lot of these early sets, especially the 12V portables, even when the coupling capacitors in the vertical amplifier circuit were new, they often still struggled to just attain satisfactory vertical linearly, especially near the end of the vertical scan and any deterioration of the electrolytics becomes really obvious.

In these small Sony sets of the early 1960's they also suffered from Horizontal linearity defects, but this was nothing to do with electrolytic capacitors, it was because they did not incorporate an S correction capacitor , or a magnetic saturable linearity coil. So if you look at the H linearity carefully you will find the the right side of the scan a little more stretched than the center and the left side significantly more stretched than the center.


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 Post subject: Re: Sony Micro TV with no audio
PostPosted: Oct Sun 18, 2020 1:51 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 17961
Location: Utica, NY 13502 (USA)
ACORNVALVE - All of what you have said here is true but the title of this thread says "...TV with no audio" which is what I was focusing on. Of course many other problems could contribute to 'no audio' as well but bad caps was my first thought.

Dave


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 Post subject: Re: Sony Micro TV with no audio
PostPosted: Oct Mon 19, 2020 12:28 am 
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Joined: Jan Thu 16, 2020 12:29 am
Posts: 768
Dave Doughty wrote:
ACORNVALVE - All of what you have said here is true but the title of this thread says "...TV with no audio" which is what I was focusing on. Of course many other problems could contribute to 'no audio' as well but bad caps was my first thought.

Dave


But it was no audio, after recapping, so presumably it cannot be a bad capacitor now, more likely a problem induced by the recapping process, since the audio worked before the caps were replaced.

There is a tendency to blame faults on bad caps, which is why many go for a recapping off the bat and with vintage tube gear with bad waxies and very old dried up electrolytics, it may well be a suitable move for that equipment.

But for small size vintage transistor TV's, especially of the 1960's era, not so great as an initial move, better to do diagnostics to determine the faulty parts and replace the minimum parts with a targeted repair, especially in light of the more crowded construction and more fragile nature of the pcb's and transistors in these sets.

One problem in the repair of all electronic gear, if some "global hammer" is used, like replace all the caps, or even re-flow all the solder joints, if the set is not tried after each part is replaced and as a result a fault is introduced by the repair/replacement, there could be a dozen or more locations where the problem occurred and the person is left bewildered. This is one reason why one at a time intervention (single part replacement & then re-testing) is much better, but it takes something that is becoming a rare trait in the world these days, patience as it can be a much more time consuming process.


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