Color blobs + speaker buzz in Sylvania Superset

[TrllVl90]

Hey guys,

I've got a Superset console from the late 80s that I grew up watching. I read that these tubes were driven pretty hard, so I'm not surprised the picture isn't 100%.

I've never had a problem starting it up, no arcing noises (maybe a few minutes to warm up, because I leave it unplugged).

But the past few years it's had big red and blue blobs on the screen. I think maybe the gun isn't turning off the colors at the correct scanning point.

Also there's a buzz in the speaker that either fades in and out slowly (like over the course of 10-20 seconds) or changes volume based on how bright the image is.

The only video I could find on youtube presenting the color problem (in a different model) is in Hindi, and other than him saying the output voltage of a capacitor is 100V and should be 180V at one point, I'm not sure why he's changing the capacitor he's changing, but he's replacing a 4.7uF cap with a 10uF cap.

Here's that video: https://www.youtube.com/watch?v=bFl5OP_7FIo&t=6s

Any help any of you could provide would be great. I did find a SAMS for this TV, and I'm reading through it, but circuit analysis was my weakest subject when I got my EET.

Here's an album of the details of my set (note: there are 6potentiometers accessible through the front control, I have everything turned to the max in this album; but even turning things down doesn't eliminate the blobs or buzz): https://imgur.com/a/ZqS9k4K

Here's a quick video look of the main chassis board components: https://www.youtube.com/watch?v=spXMa0TBw60

I haven't pulled the board out because I haven't discharged the tube yet, as it says to use the "DAG ground" and that the chassis ground isn't suitable, and I'm not sure what that is (I have done some searching around here to o success, I'll re-read the SAMS again, I probably overlooked it.)

Thanks in advance for any advice you can provide, I love this set and really just want to get it into a shape where I can watch a VHS or something every now and again.

And if you need anymore information, please let me know, I provided everything I could think of based off of other posts, but I'm sure I missed something.

Sean

[zeno]

The cap being changed is the boost A.K.A. 200V filter cap. One of the
most common problems on any brand. Can cause many symptoms inc.
looking like a bad CRT. The 200V runs the 3 video outs R, G & B.

Buzz I dont know BUT many NAP sets got noisy yokes in the vert winding.
Cure was to spray it with something from the hardware store but I forgot what.

Keep in mind these sets have 3 grounds. Hot, cold & HV. To discharge
short between HV & outer CRT coating ( dag).

Blob usually purity. Degauss ( DGS ) may not be working. Neck components moved. Broken DGS thermistor, cold joint.....

Last is pull chassis & go over the PCB real good for cold joints especially
around the HOZ & flyback. Almost guarrantied to have some.

Good luck
Zeno
LFOD !

[TrllVl90]

Thanks, man! I have somewhere to start now! I'll probably pull the chassis and check everything over, just to be sure.

I'll have to look through the forums more, maybe there's a thread where that spray is mentioned. I assumed it was a signal leak into the audio circuit.

[zeno]

Originally Posted by TrllVl90

Thanks, man! I have somewhere to start now! I'll probably pull the chassis and check everything over, just to be sure.

I'll have to look through the forums more, maybe there's a thread where that spray is mentioned. I assumed it was a signal leak into the audio circuit.

The yoke buzz is mechanical. If its from the SPK only its an audio problem.

[TrllVl90]

Originally Posted by zeno

The yoke buzz is mechanical. If its from the SPK only its an audio problem.

Yeah the buzz is from the speaker only. All is quiet from the tube.

[TrllVl90]

Hey, looking over the board, there's a thermistor (R403) listed as "NTC 18.4 Cold" that is toasted and split open.

The manual says to replace it with the same thing. The only part number give is "2303240001". And,when searched online, other than Sears Parts Direct (which says it's discontinued, and there's no equivalent available), I've had no luck finding any information on this thermistor.

Have any of you run into this in another TV, or know about this therm?

[zeno]

Thats the DGS thermistor. You can use one out of a junker or
often solder it back together. Its the reason for your blobs.When cold
& set turns on it applies AC to the DGS coil for < a second then goes open,
if it didnt the fuse would blow. It may take a few cold starts for the blob
to go away. 120 ohms cold is a common value.

Zeno

[TrllVl90]

Ahhhh! Dude, that's super helpful! I did find one of the electrolytics near the flyback popped out the bottom as well, I think it's that boost capacitor you mentioned.

Is there any common amperage rating I should aim for? The input according to the SAMS is 120V/900mA, but the voltage going into the degaussing circuitry is 76V or 78V.

I can always measure the current flow through there.

Either way, here's the snippet of that circuitry. I can not believe I read "Degaussing coil" at least 5 times, and didn't put it together.

https://imgur.com/a/2QFaB4U

Thanks again, man. You've been extremely helpful!

[zeno]

Dont remember this circuit but it seems to use a triac for switching.
The 120 cold should work but a bit slower. If not you may have to find an original OEM part.
Uses the # 2303240001 OR 230324-1 for your search.
BTW this set has a chassis ## & that helps us. Its on a tag & the format
is like 25C2##-##..........

[TrllVl90]

Okay. There's a tag on the back panel of the set that says "Chassis No 26C8-07", I'll check the board itself when I get back to work tomorrow.

I'd be thrilled if the 120 Cold works, even if it is a bit slower. Would it cause any damage to try it?

[damen]

I thought the 120 cold ones were used with the black plastic looking varistors and they decreased in value when heated. The 18.4 cold ones were in series with the degaussing coil and they increased in value as they heated up.

[TrllVl90]

Originally Posted by zeno

Dont remember this circuit but it seems to use a triac for switching.
The 120 cold should work but a bit slower. If not you may have to find an original OEM part.
Uses the # 2303240001 OR 230324-1 for your search.
BTW this set has a chassis ## & that helps us. Its on a tag & the format
is like 25C2##-##..........

Hi!

The circuit diagram in the SAMS has a "10.1 PTC Cold" thermistor in series with the degaussing coil; parallel to that is the 18.4 NTC Cold preceding an array of capacitors and diodes.



Also, the board itself had no numbers on it similar to that, but luckily I took a picture of the tag on the back of the set, which read (and is formatted like):

Chassis No.
26C8-07 AA
592275-7

Note: the AA is in black ink and kind of on its own, where as the rest of the tag is in brown ink.

Thanks guys!

[zeno]

OK its a C-8. family set. All the numbers after that indicate
changes / additions etc to the main chassis. Any C-8 manual
will show 95% of it.
Only problem wrong thermister would cause is a blown fuse. I am
trying to remember the value of the common one but I have CRS !
The 120 ohm went back to the old tube days & into the '80s at least.
It may be best to track down the OEM part & work on the audio for now.
If the blobs drive you nuts you can build a DGS coil or use a soldering
gun to DGS it for now.

Zeno

[TrllVl90]

Cracked as it is the thermistor measures 34-40 ohms at room temperature. I can't imagine that's the correct resistance though.

Do you have any idea how to go about tracking down an oem thermistor? I've typed in all combinations of information I can get from it in Google, Mouser, and Digikey; and the only result I got was on Google from. a Sears Parts Direct link that just told me the part was discontinued.

I also can't imagine Sylvania would know anything about it anymore.

[old_tv_nut]

searching "degaussing thermistor" on ebay came up with a lot of hits - not sure if they are suitable, but have a look.