Sony TV-770 dim CRT.Sound OK.

[centralradio]

Hi to all Videokarma.

I have Sony TV-770 here which has a dim CRT"Low brightness" .Sound OK .I'm questioning if the CRT could be bad.Hard to see if filament is lit....Also notice the pix cathode voltage is around 25 volts at full brightness which supposed too be 37 volts..B+ 12 volts is good...

Photo of set and Schema available at:

https://www.radiomuseum.org/r/sony_t...er_tv_770.html

Has anybody worked on this kind of set....

Thanks in advance.

[zeno]

Most likely the CRT.
Cathode voltage goes down as your brite goes up.
If it slowly gets better with time its another sign the CRT is weak

73 Zeno
LFOD !

[Electronic M]

Originally Posted by centralradio

Hi to all Videokarma.

I have Sony TV-770 here which has a dim CRT"Low brightness" .Sound OK .I'm questioning if the CRT could be bad.Hard to see if filament is lit....Also notice the pix cathode voltage is around 25 volts at full brightness which supposed too be 37 volts..B+ 12 volts is good...

Photo of set and Schema available at:

https://www.radiomuseum.org/r/sony_t...er_tv_770.html

Has anybody worked on this kind of set....

Thanks in advance.

Some of us aren't members of radio museeum and can't read their schematics....IIRC they charge money or want you to scan documents to get access and I don't want to deal with that.

[centralradio]

Originally Posted by zeno

Most likely the CRT.
Cathode voltage goes down as your brite goes up.
If it slowly gets better with time its another sign the CRT is weak

73 Zeno
LFOD !

Originally Posted by Electronic M

Some of us aren't members of radio museeum and can't read their schematics....IIRC they charge money or want you to scan documents to get access and I don't want to deal with that.

Hi Electronic M and Zeno and all VK........

I agree Zeno .I think the CRT is done.Years ago as I looked at this set and said then the CRT is shot..Maybe the note came off but I got to put notes and dates on this stuff I check.

Electronic M .I'm not a member at RM .
Dont donate manuals and or refuse to be a member of Radio Museum because I'm not a fan of their no share policy there .They let you download a few pages a week for free and thats how I got the 2 pages of the TV Schematic..

My favorite schematics and service manual source is https://www.sharefx.com// Nice people there. Free membership and free downloads up to 100 service manuals daily..Make a request and if they have it .They will upload it for you........................

I do have a couple 7 inch Sony's here.I could check if its the same CRT and even see the TV-770 chassis is OK.I think they are the TV-720's .I'll be looking at the TV-720's soon anyway and probably post about them in this small TV forum.... .


Thank you both for your input...

[Popester]

You could always find a eBay set and buy it for the jug. I see that model often on eBay. I believe that was a early to mid ‘70’s era set.

[centralradio]

Originally Posted by Popester

You could always find a eBay set and buy it for the jug. I see that model often on eBay. I believe that was a early to mid ‘70’s era set.

Thanks for the info.I'll check it out in case the TV-720 tubes are not the same animal.