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 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Wed 14, 2020 3:09 am 
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Joined: Aug Sun 23, 2015 12:44 am
Posts: 39
Hi Tom,

Thanks! That will be tomorrows project. Ill report what happens.

Steve


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 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Wed 14, 2020 3:10 pm 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 2642
Location: Dallas, TX
Sorry Steve, I had another project yesterday that kept me away from the discussion.
Sure R46 on SAMS is the same as R125 in Rider's.
If the voltage is lower on a cap than it's rating and it is getting hot either the cap is bad or the voltage is reversed. (Reversing the voltage will damage a good cap by the way.) I suppose there could be a rare case where because of a fault somewhere else there are high voltage pulses on the voltage that a meter might not register because they are so brief.
The fact that the metal cap of a electrolytic capacitor (which is the negative terminal) is insulated from the chassis (ground) in some units throws some people and they mistakenly connect the negative terminal of replacement caps to ground. This set seems to have a lot of caps insulated from ground.

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Tim
It's not the Destination, It's the Journey.


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 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Wed 14, 2020 10:04 pm 
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Joined: Aug Sun 23, 2015 12:44 am
Posts: 39
Hi Tim,

Thats perfectly ok.
The capacitor C116c IS connected correctly. Negative on cap to B- (as opposed to chassis ground). Across the cap -35vdc. Tom suggests that i check R153 and R154. I more than welcome your thoughts.

Steve


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 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Wed 14, 2020 11:42 pm 
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Joined: May Thu 14, 2015 4:15 pm
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Location: Dallas, TX
The only thing is if that cap is rated for 450V as you said, why is it overheated with only 35V on it.
You do mean that the positive terminal is 35V more positive than the negative case, don't you?
Saying that the cap has -35V across it is misleading.
Polarity is critical with electrolytic caps.

Typically the thing to do is check the voltages starting at the power transformer and proceeding towards C116C.

I assume that you disconnected the added cables to the 6AT6. They look to be coax, it is very easy to short coax when soldering by melting the inner insulation.

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 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Thu 15, 2020 12:00 am 
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Joined: Aug Sun 23, 2015 12:44 am
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Hi Tim,

Cap has -35 volts with respect to negative can. 195vdc with respect to chassis ground.

Steve


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 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Thu 15, 2020 12:03 am 
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Joined: Aug Sun 23, 2015 12:44 am
Posts: 39
Tim,

Forget to mention, i measured 115ma in series with the cap. Plus side of cap.

Steve


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 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Thu 15, 2020 12:07 am 
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Joined: Aug Sun 23, 2015 12:44 am
Posts: 39
Tim,

Those cables are gone. they ARE coax.

Steve


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 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Thu 15, 2020 12:30 am 
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Joined: Aug Sun 23, 2015 12:44 am
Posts: 39
Tim,

This seems odd, from + on cap to ground, AC VOLTS 438VAC. Make sense? should i use a blocking capacitor for that measurement?

Steve


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 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Thu 15, 2020 1:23 am 
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Joined: Aug Sun 23, 2015 12:44 am
Posts: 39
Made the ACV measurement again with blocking capacitor, No AC present.

steve


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 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Thu 15, 2020 3:27 am 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 2642
Location: Dallas, TX
SJK wrote:
Hi Tim,

Cap has -35 volts with respect to negative can. 195vdc with respect to chassis ground.

Steve

See that is wrong! The terminal should always be positive with respect to the can.
The current that you measured is much too high (if it is DC current). The capacitor is reverse biased and that makes it conduct DC current and heat up. It is probably ruined.
Looking at the schematic a reverse 35V on C116C and the positive terminal being 195V positive with respect to ground would indicate about 230V on C128A which would also be the voltage of the can of C116C with respect to ground.
I don't know why the voltages are like that but something is very wrong. The can of C128A should be at -85V with respect to ground, C128A's positive terminal should be connected to ground.
The can of C116C should be connected to the can of C128A, so it also should be at -85V with respect to ground. The positive of C116C should be at 150V with respect to ground.

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 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Thu 15, 2020 3:51 am 
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Joined: May Thu 14, 2015 4:15 pm
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Location: Dallas, TX
The voltages on the schematic unless noted otherwise are with respect to ground (chassis).
Most of the voltages are determined by resistor and the amount of current drawn by the connected circuits. If the currents are wrong the voltages will not be divided up correctly so they will be wrong.
It is a bit like a chicken or the egg situation, if the currents are wrong the voltage will be wrong and if the voltages are way off the currents will be wrong.
You will need to start where the voltage source is, the voltage across C128B and C131A (those caps are wired in parallel) is the source voltage. Since there positive terminals are shown as 280V with respect to ground and the cans (negative) are shown to be -85V with respect to ground to total difference that would be across C128A or C131A should be 365V. There will be some ripple (AC) across those capacitors because it is straight off the rectifier tube V112 and before the field coil which would filter most of the ripple out.

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 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Thu 15, 2020 4:48 am 
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Joined: Aug Sun 23, 2015 12:44 am
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Tim


I made a big mistake by replacing all the electrolytics at once. i usually do a few at a time. this time, i got BOLD, and did them all! Big mistake!! with the replacements, things look different. tougher to identify the caps. One thing i did do, replaced all caps per the original. when i first got this chassis, c116 was overheating then! someone made a mistake which i must have duplicated. Pulling out my hair, and thats difficult to do, IM BALD!!

Steve


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 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Thu 15, 2020 6:29 am 
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Joined: Apr Thu 14, 2016 8:25 pm
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Location: pensacola fl
Hi hope I can help here. I am going to run you around in a circle. I am using the riders diagram to work from that was linked here. It was already mentioned that you check the divider resistors but the connection to ground between r154a and r154b may be faulty. Now if your -85 is high with respect to chassis ground and r153b is good then check the ion trap coil as it can open and the 85 volt supply will go up. If it is bad you can replace it with a 36ohm 10w resistor and put an ion trap on the crt. Also the voltage divider also includes the focus coil and its control and resistors, r129, r168, and r169. An open here will reduce the current in this divider throwing off the voltages but that does not stop yet. The last part of this divider is the horiz centering r166 and the vertical centering r152. An open in this area may also get c132 very upset so it is the least likely source of the voltage imbalance. An open focus coil will upset it as well and it can also be replaced with a 250 ohm 25 watt resistor and a permanent magnet focus magnet placed on the crt as with the ion trap coil if it is bad a permanent magnet trap will work fine. Hope this helps and good luck.


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 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Thu 15, 2020 12:56 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Rockaway , nj 07866
I once had a electroyltic rated for 450 volts start popping and was hot , it had about 200 volts running through it and it was new , so a new part can be bad , wouldn't hurt to suspect it is no good


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 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Thu 15, 2020 3:33 pm 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 2642
Location: Dallas, TX
I doubt if a component failure would cause the polarity to be reversed on C116C, although the power supply dividing circuit is complicate enough that it might happen somehow.

Steve, did you use new cans or separate capacitors to replace the original cans?
If you used new cans then the other sections of C116 will also be reversed.
Have you seen Phil's article about his restore of a RCA 721?
https://www.antiqueradio.org/RCA721TCSTelevision.htm
He used separate capacitors under the chassis.

Since C116C is used to filter the +150V supply more, normally the capacitor does not have a role in determining the voltage. However because of the reverse current passing through C116C now it upsets the voltage division. You could disconnect C116C and see if the voltages would then be more normal.

I think you are going to go through the dirty job of tracing down the wiring to see where the problem is. Maybe more that one mis-wire.

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Tim
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 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Fri 16, 2020 1:47 am 
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Joined: Aug Sun 23, 2015 12:44 am
Posts: 39
Hi Tim,

Ok, not at all a problem.

I did some wire tracing, Now, I have High Voltage! May have been a miswire. Last night i was up till 4am. My head was spinning! Tomorrow, i may try my test crt to see what may be happening. No more overheating caps! At least, It's a start!

Steve


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 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Fri 16, 2020 4:50 am 
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Of course we all want to know what you did to fix it.

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 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Fri 16, 2020 4:52 am 
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Absolutely! Tell us!

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 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Tue 20, 2020 10:16 pm 
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Joined: Aug Sun 23, 2015 12:44 am
Posts: 39
Hello Guys,

I'm currently dealing with vertigo. Trying to fix a tv with vertigo is a very interesting combination. What i was able to determine I have high voltage and one inch of horizontal deflection, no vertical deflection. Swapped out 6SN7's etc, same result. That power supply still mystifies
me. Sams photofacts today give Key Voltage Points. Back in '47, I guess not. For example, the bleeder box {rca's term}, on which terminal there, should i find what voltage, as well as any other thoughts you may have. Never experienced anything like this chassis before. I'll very much appreciate any ideas.


Steve


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 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Tue 20, 2020 10:57 pm 
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TVs don't get vertigo, but people do.

As for voltages early Sam's have a voltage chart that gives voltages on each pin of the socket it's on its own sheet of the folder separate from the schematic page. By the mid 50s Sam's dropped the spearate chart and listed the voltages on the schematic page.


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