Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Nov Thu 26, 2020 2:23 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 58 posts ]  Go to page 1, 2, 3  Next
Author Message
 Post subject: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Mon 12, 2020 8:48 pm 
Member

Joined: Aug Sun 23, 2015 12:44 am
Posts: 39
Hello Everyone,

I'm working on the above chassis. replaced all electrolytic capacitors observing proper polarity etc. I also replaced all paper tubular caps. All I'm getting is a very low hum from speaker. on initial power up, I noticed C-116C running hot. I naturally assumed that that cap was either very leaky or shorted. After replacing all the caps, C-116C is still running very hot. I don't apply power very long as I don't want the capacitor to vent. I felt very confident that after the replacement of the caps the overheating would stop. This power supply is a bit complex. Has anyone experienced a similar problem in this chassis? My question is, why would a properly connected electrolytic cap overheat? I tried several different capacitors, same result. Any help would be very much appreciated.

Steve


Top
 Profile  
 
 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Mon 12, 2020 8:58 pm 
Member
User avatar

Joined: Mar Sun 01, 2009 10:27 pm
Posts: 5382
Location: Ann Arbor, MI
Edited:
One possible cause of a new cap heating up is that it is installed backwards.
If the cap is connected to a lower voltage B+ supplied by a voltage divider, an open resistor to ground could cause the voltage on the cap to be too high.

_________________
Tom


Last edited by Tom Schulz on Oct Mon 12, 2020 9:11 pm, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Mon 12, 2020 9:11 pm 
Member

Joined: Aug Sun 23, 2015 12:44 am
Posts: 39
Cap is installed per the original can type.

Steve


Last edited by SJK on Oct Tue 13, 2020 2:05 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Mon 12, 2020 9:14 pm 
Member
User avatar

Joined: Mar Sun 01, 2009 10:27 pm
Posts: 5382
Location: Ann Arbor, MI
I just edited my post. See the new part.

_________________
Tom


Top
 Profile  
 
 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Mon 12, 2020 11:58 pm 
Member

Joined: Aug Sun 23, 2015 12:44 am
Posts: 39
Hi Tom,

I measured the voltage on c116c with respect to B- -25volts. with respect to ground 195 vdc.
caps are rated 450wv.

Steve


Top
 Profile  
 
 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Tue 13, 2020 1:13 am 
Member

Joined: Apr Sat 06, 2013 2:18 pm
Posts: 570
Location: New Hampshire
Without seeing the schematic....... Typically you have raw B+
off the rectifiers. Then a filter cap ( call it C1 ). Then through a choke.
Then another filter cap ( C2). This make a Pi network. At C2 you have
your main B+ for the horz output & the divider for the rest of the sets
lower B+ voltages. If C1 opens C2 will heat up & also open in time.

Not to beat you up but I am on 2 forums for old TV's. Sets that are re capped
en-masse & suddenly stop working are COMMON. Do your recaps a few at a time
& recheck as you go.
Goal is to get a raster first so you can evaluate the set then fix it one stage
at a time.

73 Zeno 8)
LFOD !


Top
 Profile  
 
 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Tue 13, 2020 1:19 am 
Member

Joined: May Sun 07, 2017 11:35 am
Posts: 1149
Location: Belrose, NSW, Australia
Agree, and what's more, such faults can be very hard to find, requiring tedious and thorough point-by-point comparison with the schematic.

And sometimes the schematic has errors!

_________________
Wax, paper, bitumen, cotton, high voltages - what could possibly go wrong?


Top
 Profile  
 
 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Tue 13, 2020 1:58 am 
Member

Joined: Aug Sun 23, 2015 12:44 am
Posts: 39
I'm uploading Service Data for this receiver. I would be very appreciative for any help you all can provide.

Steve


Attachments:
rca_721ts_rider_tv1.pdf [5 MiB]
Downloaded 21 times
Top
 Profile  
 
 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Tue 13, 2020 2:48 am 
Member
User avatar

Joined: Mar Sun 01, 2009 10:27 pm
Posts: 5382
Location: Ann Arbor, MI
At the first reading of the original post I was left with the impression that the original cap overheated and now the replacement is overheating. After re-reading that post, I am not sure that I understood that correctly.

Another thing to consider. New parts can be bad. Perhaps try another new cap.

_________________
Tom


Top
 Profile  
 
 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Tue 13, 2020 3:31 am 
Member

Joined: Aug Sun 23, 2015 12:44 am
Posts: 39
Hi Tom,

Your original understanding is correct. It surprised me to see the new cap overheat as well. I tried several, thinking in the off chance, one cap is bad. All showed the same result. All caps rated 450wv.

Steve


Top
 Profile  
 
 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Tue 13, 2020 11:54 am 
Member

Joined: May Sun 07, 2017 11:35 am
Posts: 1149
Location: Belrose, NSW, Australia
How physically large is the new cap?

In that voltage doubler circuit one cap is required to handle the full B+ current of the TV. Small caps cannot do that. You need a cap rated for at least 1 amp ripple current. There are special parts for this job. The foil in the cap is plain, not etched, and as a result it is bigger.

_________________
Wax, paper, bitumen, cotton, high voltages - what could possibly go wrong?


Top
 Profile  
 
 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Tue 13, 2020 5:01 pm 
Member
User avatar

Joined: Mar Sun 01, 2009 10:27 pm
Posts: 5382
Location: Ann Arbor, MI
According to the posted schematic, there is no voltage doubler.
Perhaps some odd failure in the voltage devider or some incorrect repairs from some previous person is causing the voltage on that cap to be reversed. Measure the voltage on it again and check the polarity of the voltage you are actually getting instead of polarity you should have. If it is reversed, check all the sections of R154 and R153.

_________________
Tom


Top
 Profile  
 
 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Tue 13, 2020 6:00 pm 
Member

Joined: May Thu 14, 2015 4:15 pm
Posts: 2642
Location: Dallas, TX
C116C should have about 235V across it. C116C's positive terminal should be connected to R153 and R154 as well as R125 near the video output.
C116 should have it's case isolated from ground. The case should be at about -85V with respect to ground.
That set has a rather complicated supply circuit.

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


Top
 Profile  
 
 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Wed 14, 2020 12:36 am 
Member

Joined: Aug Sun 23, 2015 12:44 am
Posts: 39
My thanks to everyone trying to help me tackle this problem.


Hi Tim,

I cannot locate R125. It's in parts list, i cant find it on the schematic. I don't see it in resister locater either. 10Meg resister.
Across C116 is -35 volts and slowly dropping. I measured current (DC) through c116c and got 115 ma and slowly rising, more than likely as capacitor heats up.

Steve


Top
 Profile  
 
 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Wed 14, 2020 1:17 am 
Member
User avatar

Joined: Mar Sun 01, 2009 10:27 pm
Posts: 5382
Location: Ann Arbor, MI
SJK wrote:
My thanks to everyone trying to help me tackle this problem.
Hi Tim,

I cannot locate R125. It's in parts list, i cant find it on the schematic. I don't see it in resister locater either. 10Meg resister.
Steve

Look at the schematic you posted. Find the CRT on the schematic. Immediately to the left of the CRT on the schematic is R125.

SJK wrote:
Across C116 is -35 volts and slowly dropping. I measured current (DC) through c116c and got 115 ma and slowly rising, more than likely as capacitor heats up.
Steve


Do you have negative 35 volts ( -35 ) at the lead of the cap that should be the positive lead? If so, that is the reason for the cap heating up.

_________________
Tom


Top
 Profile  
 
 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Wed 14, 2020 1:38 am 
Member

Joined: Aug Sun 23, 2015 12:44 am
Posts: 39
Tim,

YES! -35 volts.

Someone added 2 cables that are connected to the 6AT6. Im not sure if this Jimmyrig is related to this problem or not.

steve


Attachments:
20201013_201306[42].jpg
20201013_201306[42].jpg [ 1.88 MiB | Viewed 484 times ]
20201013_201537[41].jpg
20201013_201537[41].jpg [ 3.35 MiB | Viewed 484 times ]
Top
 Profile  
 
 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Wed 14, 2020 1:49 am 
Member

Joined: Aug Sun 23, 2015 12:44 am
Posts: 39
YES negative 35 volts is present. isent 2 photos of cables connected to the 6AT6. not sure whether this is related to this problem. cables are hot.


Top
 Profile  
 
 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Wed 14, 2020 1:51 am 
Member

Joined: Aug Sun 23, 2015 12:44 am
Posts: 39
Tim
I have a feeling that ill be cutting those cables out. Doesnt look like RCA work.

Steve


Top
 Profile  
 
 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Wed 14, 2020 2:05 am 
Member

Joined: Aug Sun 23, 2015 12:44 am
Posts: 39
Tim,

This is PHOTOFACT 70-7. COMPARE TO OTHER SCHEMATIC. CORRECT ME IF IM WRONG, LOOKS LIKE R125 is R46 on this schematic


Steve


Attachments:
0070_7n.pdf [2.81 MiB]
Downloaded 11 times
Top
 Profile  
 
 Post subject: Re: HELP NEEDED FOR RCA KCS-26 CHASSIS
PostPosted: Oct Wed 14, 2020 2:51 am 
Member
User avatar

Joined: Mar Sun 01, 2009 10:27 pm
Posts: 5382
Location: Ann Arbor, MI
SJK wrote:
Tim,
This is PHOTOFACT 70-7. COMPARE TO OTHER SCHEMATIC. CORRECT ME IF IM WRONG, LOOKS LIKE R125 is R46 on this schematic
Steve

Yes, R125 is R46 on that schematic.

Those cables look like someone wanted to bring out the sound out to a stereo system or some such. They would not be the cause of your problem as they could not upset the voltages on your overheating cap.

Just to be clear, an electrolytic cap will act somewhat like a shorted cap if the DC voltage across it is reversed.

I would check all the sections of R154 and R153. Check for open or high value sections . Also, if those are the type of resistor I think they are, there could be internal shorts to the chassis.

_________________
Tom


Top
 Profile  
 
Post New Topic Post Reply  [ 58 posts ]  Moderators: Mr. Detrola, 7jp4-guy Go to page 1, 2, 3  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: bheggeseth and 9 guests



Search for:
Jump to:  




































Privacy Policy :: Powered by phpBB