Sylvania Superset Update

[TrllVl90]

I checked the filament voltage and got 2.2 (or 1.5 if I used the low-impedance setting). Both seem wildly incorrect. Would the retrace-cap value being low also drop the voktage? I know I got some cheap ones, but I'm not certain what the effects of high capacitance vs low capacitance are in the circuit.

Also I'm assuming I measured correctly. I measured across the two filament joints (in my case pins 9 &10).

Thanks in advance.

Edit: I also tested the voltage within a couple minutes of turning it on rather than waiting until the image became clearer. If that matters.

[old_tv_nut]

You must use a True RMS (TRMS) meter, not an ordinary multimeter (average reading), because the voltage is pulsed.

[TrllVl90]

Originally Posted by old_tv_nut

You must use a True RMS (TRMS) meter, not an ordinary multimeter (average reading), because the voltage is pulsed.

I used a Fluke 114, which claims to be TRMS. Unless there's a way to turn on and off TRMS, I did read the manual, but couldn't find anything that said that so I assumed the AC setting would work as TRMS as default. But yeah it said 2.2 and would waver around there between like 2.17 and 2.29.

[JohnCT]

Originally Posted by TrllVl90

I checked the filament voltage and got 2.2 (or 1.5 if I used the low-impedance setting). Both seem wildly incorrect. Would the retrace-cap value being low also drop the voktage? I know I got some cheap ones, but I'm not certain what the effects of high capacitance vs low capacitance are in the circuit.

Also I'm assuming I measured correctly. I measured across the two filament joints (in my case pins 9 &10).

Thanks in advance.

Edit: I also tested the voltage within a couple minutes of turning it on rather than waiting until the image became clearer. If that matters.

I don't think the tube would even light at 2.2V. The meter is on "AC" (~), correct?

Have you verified the meter? Try it on your wall plug to see if you are getting about 120VAC.

If the retrace cap is low in value, the HV and filament would be high.

I don't recall the pin numbers of the filaments, but they should read very low ohms (power off) across the filament pins (couple of ohms) if you are on the right pins.

Since sweep is regulated, the voltage will be the same hot or cold.

John

[TrllVl90]

Originally Posted by JohnCT

I don't think the tube would even light at 2.2V. The meter is on "AC" (~), correct?

Have you verified the meter? Try it on your wall plug to see if you are getting about 120VAC.

If the retrace cap is low in value, the HV and filament would be high.

I don't recall the pin numbers of the filaments, but they should read very low ohms (power off) across the filament pins (couple of ohms) if you are on the right pins.

Since sweep is regulated, the voltage will be the same hot or cold.

John

Hey John,


Yeah the meter gets calibrated everyb6 months for my works IDK certification stuff, I set it to AC for sure, I even did it again after watching a movie a couple hours later just to confirm.

The pin numbers are 9 and 10. I measured across those.

I also included pictures from the manual of the circuitry and board.

I feel like I've clearly done something wrong, but I don't know what it is.

[old_tv_nut]

Hmmm - if you are reading different voltages with the high and low impedance settings, it seems to me the filament voltage source may actually be open circuit somewhere and you may be just picking up some capacitively coupled pulses - check the filament supply for continuity.

[zeno]

22 volts is normal IF you look at it with a scope.
They are hoz spikes from the FBT. The meter is trying
to average what it sees. Different meters may show different
readings.

73 Zeno
LFOD !

[TrllVl90]

Hmm. Well it'll be until next week that I get access to that multimeter again. I should ask and see if work has a scope I could borrow as well. I'll also do continuity checks all around the board.

[JohnCT]

Originally Posted by TrllVl90

Hey John,


Yeah the meter gets calibrated everyb6 months for my works IDK certification stuff, I set it to AC for sure, I even did it again after watching a movie a couple hours later just to confirm.

I've never seen a Fluke TRMS meter not read accurately on scan derived filaments, but then I've never used that particular meter either..

If you can borrow a scope, you can measure the p-p of the pulse, should be 22V.

What was the value of the original retrace cap and what is the value of the one you installed? (I might have missed that)


John

[TrllVl90]

The original cap value was 22 uF 250V, I bought a cheap pack of 10 at the same value, I didn't think to check before I installed, but I'll check the others maybe one is real close to the original value.

[jr_tech]

Originally Posted by JohnCT

I've never seen a Fluke TRMS meter not read accurately on scan derived filaments, but then I've never used that particular meter either..

The 114 is an electricians model...some compromises may be made to reduce/eliminate ghost readings.

https://www.fluke.com/en-us/product/...ters/fluke-114

Looks like TRMS readings are only specified to 1 khz... might be way off at 15 khz.

jr

[JohnCT]

Originally Posted by TrllVl90

The original cap value was 22 uF 250V, I bought a cheap pack of 10 at the same value, I didn't think to check before I installed, but I'll check the others maybe one is real close to the original value.

That's not the retrace cap - that's the B+ bypass cap off the flyback. The retrace will be a 1500V film cap. If B+ bypass cap opens, the pulse from the horiz output will feed back to the regulator and cause start up and shutdown. While it's possible, I don't see retrace caps fail in anything but a binary fashion (good or bad), but I do remember one particular RCA that used a retrace cap with two or more sections in series. One section shorted, the value of the cap increased, the HV went down and the horizontal scan went very wide. That was the only one I remember that went off value.

Sounds like you're down to proper set up and a weakish picture tube.

John

[jbattles]

yeah, man your tube is worn got to face it. now adjust you contrast down to where it does not smear and just watch it. those nap sets always smear when contrast is turned up. there were like that out of the box. to me the picture was always not the best.

[jbattles]

yeah, man your tube is worn gotta face it. when brightness is set where you have a good bright picture and the contrast is set at a picture that is acceptable picture. then it starts to smear and you turn it down and you still cant get a good picture tube is worn. one of the pictures posted looked like that contrast was to high adjust it and it would decent picture.

[TrllVl90]

Originally Posted by jbattles

yeah, man your tube is worn gotta face it. when brightness is set where you have a good bright picture and the contrast is set at a picture that is acceptable picture. then it starts to smear and you turn it down and you still cant get a good picture tube is worn. one of the pictures posted looked like that contrast was to high adjust it and it would decent picture.

I kinda figured. It got used heavily while I was growing up. I'm really only using it to watch VHS tapes about once a week (maybe less if I'm busy) anymore. The picture is pretty good with contrast at like 2/3 turned up and brightness up a little bit, I think I need to adjust the focus, as the image was a bit crisper before I replaced the cap I did.

As for the film cap that JohnCT mentioned isn't bulged or anything, but I'll keep a lookout for one on ebay, who knows. I did find a nos PTC thermistor for the degaussing circuit.

I'll triple check the filament voltage when I get a chance, and I still have to figure out this audio buzz issue maybe a worn cap or something in the audio circuit.