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Alright so I put the diodes in, No issues. And booted it up. And once again was left with about 30 volts Then when the heaters finished heating it dropped.
I traced where the ac mains lines actually go and one goes to the damper tube base. But is not actually connected to the tube. Its connected to a sand resistor. Some one else mentioned it could have been this resistor. I measured in this resistor at 25 ohms. Is this an average value for this type of resistor or is it wayy off? The other mains goes to ground then the one of the new diodes I put in. Also one side of the mains is hooked up to a small cap then travels to another larger cap. To ground again..I think |
Make sure they are in correctly ....
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Does the resistor look burned , or have cracks in it ? |
I'm almost positive I have them in right. I get just about the same voltage as before with the originals in. Just a little better. SO i think I got that part right.
But the electrolytics are dead is the real problem. It charges up to 30 then drops to 3 volts when I turn it off. It should be staying closer to 30 for longer should it not? Anyone think replacing them would solve the problem? |
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I wouldn't say it looks burnt or anything else though. |
If you havent' already replaced the electrolytics, that is surely adding to your problem, along with bad paper capacitors.
I just don't understand how it is people take un restored stuff and put so much faith in it working. Bill Cahill |
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The rectifier circuit sounds like a doubler. One of the mains (powerline) going to ground, the other mains line going to an electroytic capacitor. The other side of that cap has a diode, the other end (its anode) of which going to ground. And a 2nd diode, where the 1st diode connects to the cap, the other end (its cathode) of the 2nd diode feeds a second electroytic cap, the other end of ths cap goes to ground. Selenium rectifiers usually had "+" marked on their cathodes, as if to say, "apply AC to the other end, and here you will get positive voltage". |
Yes it is a voltage doubler working as you described.
And as for the sand resistor it has the number 2 on it. And I thought it may be an ampere rating cause like you said "Fuseistor". And if it is supposed to actually be 2 ohms it is 23 ohms off. Is there a possibilty that this sand resistor is actually for the heaters. I sorta traced where it goes. It went to hz deflector tube (12bq6gtb) and definatley connected to pins 7 and six (7 is heater connection 6 is blank) |
Does anyone think that a recapp is all she needs and would bring this tv back from the dead? Or would it still most likely need further work?
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As someone who has repaired many a b&w tv the first thing I suspect is the high voltage(about 20kv @1ma).If you touch it you will live(unless you have a pacemaker:D)Its like getting shocked with a sparkplug wire.I know a way to check th high voltage with a screwdriver but I'm wary of telling you how in case something happens to you. These tv get dust inside and it doesn't take much to overload the H.V. You could try cleaning around the H.V.(its the part of the tv with all the dust around it.The high voltage attracts dust like an electrostatic air cleaner.If the horizontal flyback transformer is gone(part of h.v.)then its a lost cause.Be careful as some chassis were conected directly to one side of the a/c line so depending on which way the plug is in the wall the chassis may be live or not.The value of doing this is not n the tv but in the learning experience of trouble shooting.Good luck and be careful:yes:
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If you replace those two electrolytics in the voltage doubler circuit you may well get the power supply operating. Either one or both could be dried out to the point that they are no longer capable of doing their job. You will get the practice in capacitor replacement, as you have many more to go after those 2. But at least getting those done should get you back to a higher voltage level. If a fuseable resistor or sandbrick resistor opens it's almost always all or nothing--to wit you wouldn't likely be seeing the paltry 30 volts you are seeing. If you have to burn any gasoline running to the radio shop for capacitors you might as well shotgun the entire power supply and replace all the electrolytics; the odds are that they are all not long for this world if not already expired. |
"Be careful as some chassis were conected directly to one side of the a/c line so depending on which way the plug is in the wall the chassis may be live or not."
HAHa I learnt this the hard way already. Testing to see if caps are hot Zaap. I was so happy, I thought I got the HV working again. But after some thought I realized it was 60hz because thats just how it felt. Bugger I said( I also didn't think it could get me with just one hand in there...maybe 2 fingers touched) And just some test results from the caps. I got the charge to go up to 40v. They seem to be fixing themselves a little every time I power it on(30 to 40) But I don't think they will fully recover. Also I measured 60 volts ac With my tester at the same points. And it jumped around a little (40-90 vac). With this in mind could it be the caps. I wanna say yes. But if anyone thinks its a little far fetched for the caps to bring the voltage from 30 to the proper 250 or w/e it should be. please say so. Rudy |
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Alright so just wondering if these will be hard to find. Cause I've been looking online and I'm not seeing the exact values. 33 and 220 mfd and stuff
and maybe a guesstimated cost by someone? 30 mfd 300 vdc and it says 375 something ac 20 mfd 300 vdc 375 something 100 mfd 150 vdc 250 ac something 200 mfd 150 vdc 160 uf 300v and 160uf 150 v And I turned it on again. Got 45 volts. I should just turn it on 50 more times :P |
The second voltages given on those are surge voltages. Not ac voltages.
With today's higher line voltage, I reccommend highly using 450 volt filters. Bill Cahill |
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