#31
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Ok I have no voltage on the board that is supposed to have 255 v . The schematic shows the diodes with the line on it so I'm asking that line, is it the line band on the silicone diode ? I have always had a brain fart when it comes to that band on the diode. The schematic shows + and - so the would the minus be the band on the diode . What may have me messed up is the schematic shows the line as positive but the diode band is negative so I have voltage but no voltage at the cap that feeds the IF board 255 v I thought befor the voltages were there but I was wrong.
Last edited by timmy; 12-01-2017 at 07:07 PM. |
#32
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The stripe on the diode schematic symbol is the same as the stripe on the physical diode you install...It is the cathode and is counterintuitively marked with a plus on old seleniums (since B+ returns to the cathode of the diode).
https://en.wikipedia.org/wiki/Diode#...nductor_diodes
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Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
#33
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To get the equivalent 8.4V you could use a 12.6V transformer and a series diode (no filter cap) with the CRT heater. The heater will heat up the same with 8.4VAC or DC.
Or you could rectify 6.3VAC with a filter cap to get 8,4VDC to run the CRT heater. You might be able to use a CRT brightner in "parallel" mode. These used small transformers to produce around 8VAC from 6.3VAC. In the series string you have, the transformer may make the CRT heater at 8.4V@450ma look like a load of 6.3VAC@600ma.
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#34
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So then the + marked on the selenium would be the end of the diode not marked, would I be correct ? Because on the schematic it shows the cathode mark as positive so if that's a typo then I have them backwards.
Last edited by timmy; 12-02-2017 at 05:13 AM. |
#35
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I think they used to mark the terminal with a "+" that you get B+ from when AC is applied to the other terminal.
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Audiokarma |
#36
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Here is a good link to an article describing how to replace selenium rectifiers with silicon rectifiers.
http://w3hwj.com/index_files/RBSelenium2.pdf |
#37
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The + mark on a selenium is simply saying "the B plus comes out of here."
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#38
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Ok, I'm confused, it looks like I have the diodes right but I'm not getting 255 v from c2 and c3a both are 300 v rated caps at one point it was there then gone. Strange as it sounds, both caps are grounded to chassis which is one side of the ac in the other ends go to the terminals I broke off the old cap never removing any wires this is why I thought I had the diodes wrong. I reversed them and burn the ac input resistor so I put a new one in after putting the diodes back so I'm thinking is it possible to have one diode reveresed, then how to figure out which one but it seems if I change one it will short against the other.
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#39
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Do the diodes check ok? how about the input cap(c1) ? These components may have been damaged when you burned out the input resistor.
jr |
#40
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I'll see if I can describe the proper connections verbally......
Connect the unbanded end of M1 to the chassis ground. Connect the banded end of M1 to the junction of the + end of C1 and the unbanded end of M2. Connect the banded end of M2 to the junction of the + end of C2 and L10. Be sure to check the caps before you energize the circuit. I know the manufacturers of the selenium rectifiers meant well, but their "+" designation is just counter to standard schematic documentation. |
Audiokarma |
#41
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Ok now I feel like a fool I was using the base of the chassis for ground but didn't realize it's got plastic insulators so I have voltages now all along. Still don't have a raster so time to check voltages at the crt and also put the magnet on the neck where it was when I took it apart and brightness up max.
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#42
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Quote:
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#43
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The SAMs shows 410 v on pin 6and 10 and 30 v on pin 11 but I'm getting around 460 v and 40 v on these pins but I changed the 10 ohm resistor on the ac input to a 22 ohm so I may have to raise that resistor higher but even those voltages being high I thought I should still get a raster and I even tried a 12lp4 to rule out a problem with the right tube and got nothing. Also used the ion trap in all positions, nothing. Video output tube pin 9 should be 155 v but I'm getting 204 v and pin 8 130 v I'm getting 140 v .
Last edited by timmy; 12-02-2017 at 01:31 PM. |
#44
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Is the High voltage rectifier ok?
jr |
#45
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Getting almost 9 kv at the anode.
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Audiokarma |
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