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  #31  
Old 11-09-2017, 07:08 PM
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Originally Posted by jr_tech View Post
This is what I believe is one of the varactor tuning diodes in the Sinclair MTV-1 VHF tuner section (pictured above)... it is in a TO-92 style case with no markings on the flat side, just 3 color bands on the back. (I painted the red on the top for identification in my previous post)



Apparently the tuning voltage in the set can go as high as 31 volts.

Identification and/or substitution recommendations needed.

Thanks,
jr

.
Yes your right according to the fellow in England working on this set said in the posts that he too identified those varicaps and could not find replacements and did note that they had 3 colors just as you said. If we had a real schematic that may show values of sorts it may help but it's looking like a dead end for me. Looking at your pic there is green on the components and if that's moved it will probably break off as one of the pin diodes I took out one leg broke but it believe it tested leaking and they are available so that's not a problem . Would you know by the schematic what I possibly burned that killed the brightness and brought down the 45v to 26 volts.
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  #32  
Old 11-10-2017, 02:42 PM
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Would you know by the schematic what I possibly burned that killed the brightness and brought down the 45v to 26 volts.
I can only guess, but is the 3 volt supply still working? (pin 7 on the ic just behind the pots) Is the HV at the ends of the large mylar caps (standing up behind the position pot board) close to 1900 Volts?

jr
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  #33  
Old 11-10-2017, 04:00 PM
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I have 3 volts on pin 7 but the hv just bearly gets of the start line of the hv probe. Actually aside from a dark screen the pic was still visible so maybe it's the hv I knocked out.

Last edited by timmy; 11-10-2017 at 04:05 PM.
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  #34  
Old 11-10-2017, 07:00 PM
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Grasping at straws, I would check/replace the 3 electrolytic cans between the ic and the HV transformer... the surge might have injured them... the diode standing up between two of the cans could be suspect as well as the 4 transistors in the area. A very real possibility is that the regulator circuit on the ic has been damaged. I really can't guess.

jr
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  #35  
Old 11-10-2017, 07:13 PM
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Well I'll look into those caps and I have these transistors if they are bad so I'll pull one at a time and check . However if the IC is bad then it's game over because there is no info on the web about this chip. What I actually did was touched the wiper of the line amp and the 45v adjust wiper both did this. Thanks.

Last edited by timmy; 11-10-2017 at 07:28 PM.
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  #36  
Old 11-17-2017, 10:20 PM
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I still have not got supply voltage from either of the rear jacks to operate the set, I supply 5 volts to the "bat" terminal on the sound board to power the set. Likely more corroded open runs will be found... the tuner boards are plagued with corrosion. Fun project!

jr
Slaps forehead!
After checking all of the corroded traces on the tuner board which ohmed out ok, I discovered that the center pin of both the 6 and 12 volt rear connectors is NEGATIVE!
Duhh!

jr
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  #37  
Old 11-20-2017, 05:34 PM
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Slaps forehead!
After checking all of the corroded traces on the tuner board which ohmed out ok, I discovered that the center pin of both the 6 and 12 volt rear connectors is NEGATIVE!
Duhh!

jr
Yes lol the neg is in the middle not like all those plugs today are positive.
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