Recently Acquired 1969 Motorola Color Tube Tv - Page 4 - Videokarma.org TV - Video

Lain94 · #46 09-15-2022, 06:38 PM

Ok, I am now replacing just the problem capacitors for now, but the wire fuse in the power supply circuit blew so it looks like I will need a "#31 copper wire fuse" Not sure how many amps that was or what voltage rating I need though, the schematics say nothing about that. Assuming #31 means SWG than I believe that would be 8 amps. But I still need to know how many volts minimum I need for the fuse to be safe to use as a replacement.

Electronic M · #47 09-15-2022, 11:14 PM

Or just buy some 31guage wire and use the same approximate length as the original #31 fusible wire link....

Lain94 · #48 09-16-2022, 02:15 PM

I just realized there were two standards SWG and AWG. Apparantly AWG is the now more commonly used one. It does not specify whether is AWG or SWG. But SWG was a british made standard and AWG is American so I am guessing AWG. I will post an update on results after replacing the burnt fuse and bad capacitors. If I am lucky the tv will fire up without issues after appropriate repairs are made.

Lain94 · #49 09-18-2022, 10:02 PM

This wax paper safety cap. that blew appears to be on the AC side of the circuit. From what I read online electrolytic caps are not supposed to be put in for AC voltage. Also AC and DC voltage ratings for caps. are often different. Finally this wax paper cap. only shows the DC value and not AC value. This cap appears on the schematic as polarized but wax paper caps are not polarized caps. I am very confused yet again.

https://imgur.com/a/xBRTFcF

Lain94 · #50 09-18-2022, 11:35 PM

Also for replacing that wax paper safety cap I mentioned: Would this be an acceptable replacement?

https://www.mouser.com/ProductDetail...EmAOx7Mg%3D%3D

https://media.discordapp.net/attachm...687&height=478

Electronic M · #51 09-19-2022, 03:00 PM

The original appears to be a ceramic bodied paper cap....Prior to the 80s those were common in across the line RF filter duty.

You could get away with the cap you've found (I often use normal 630V film caps), but modern standards call for a X or Y rated across the line safety cap.

AC voltage is rated in RMS which is basically set up so if you had a 120V light bulb it would reciever the same energy from 120VAC RMS as it would from 120VDC which was useful a century ago when some regions had DC power and others had AC. Peak AC voltage is the square root of 2 (or 1.414) times the RMS. Peak AC voltage (about 170V) is the max instantaneous DC voltage that the cap should normally see, but usually at least double that is used as a DC rating to provide a safety margin and help the cap run cool.
It's important to know that RMS should only be applied to sine waves...Non-sinusoidal waveforms need more complex math to get RMS values, and often don't measure accurately on most AC meters since most lack a true RMS measuring circuit.

Lain94 · #52 10-07-2022, 11:21 PM

An update on the Motorola tv. I have replaced the wax paper safety cap that had blown along with the blown wire fuse. In addition I have recapped 2 additional electrolytics and what was later discovered to be a paper-oil cap. I still am going to recap any remaining paper and electrolytic caps in the tv. I have managed to get the tv back to working condition, but it appears to still need adjustments, likely convergence, color purity, and perhaps also tuning. I am suspecting perhaps a weak horizonal output tube as well since the right side of the picture is wavy sometimes.

I attached some photos to show the current status now after making the basic repairs.

https://imgur.com/a/4AimE3e

Electronic M · #53 10-07-2022, 11:52 PM

If the side is wavy that's usually AC hum on the DC rails indicating filter capacitor (or sometimes B+ doubler diode) failure.

The raster not filling the screen horizontally is potentially a sign of a weak horizontal output/damper, but could also be a sign of B+ being below spec (which could be a result of the items from the previous paragraph).

B+ voltages and tubes should be checked.

Purity and convergence aren't hard to adjust if you have the right test patterns and sufficient patience... Dynamic convergence typically requires adjusting coils. Make sure you have a plastic hex diddle stick (AKA alignment tool). Do NOT use a metal hex key. Metal keys crack the adjustible slugs easily (which is very bad), and even if you have the godlike finesse/luck not to crack them the metal tool will it's self skew the adjustment such that if you have it perfect then it will be slightly off the moment you remove the tool. These are lessons I learned the hard way on convergence don't repeat my mistakes.

Lain94 · #54 12-27-2022, 10:55 AM

A bit of a minor update. I recently acquired my first CRT tester. It is a Sencore CR 161. From what I have heard online, Sencore is a trustworthy brand. After reading the instructions and manual, I quickly learned how to use the tester and began using it to test all the CRT's I have.

The one in this motorola tv is supposed to be 6.3 volts and hi bias mode. At this voltage red and green color guns were good. Blue however was on the weak side. However at 7.3 volts which would simulate what a tube brightener would do to the emissions, emissions improved for all three guns notably, and blue went solidly into the good territory.

No shorts were found for this CRT which is good to know.

While this CRT has many hours on it, I am a bit surprised that emissions seemed higher than I would have guessed based on the alleged history and heavy use of this tv over the decades (barber shop tv). I was fairly impressed.

Lain94 · #55 03-08-2023, 01:47 AM

I used Deoxit 100 to spray into the CRT socket and tube sockets...I think I screwed the tv up. I am now only getting a horizonal line that changes color but no vertical deflection. (Same symptoms as the Heathkit tv before it ultimately failed and now has no picture or signs of life) Does Deoxit 100 cause shorting?

I fear I may have ruined the heathkit tv and likely burned the yoke coil. I turned the motorola tv off. as soon as I saw the horizontal line. (It got to that point with normal audio when the variac was turned up to around 80ish volts or so) Normally the picture gradually expands out. Also of note is that I used 99% isopropyl rubbing alcohol to try and clean the grimy pincushion circuit board (The tv sat for several days so what little water was in the mixture likely dried off for sure), I wonder if it smeared grease around on the board and may have caused a short there. I am at a loss and pretty discouraged that the tv is now worse off than where it was before.

Electronic M · #56 03-08-2023, 01:00 PM

On tube TVs at least, you generally can't harm the yoke with loss of deflection. The CRT will typically be fine as long as you turn down the brightness, or catch it reasonably fast.
Vertical sweep failure will be cause by the vertical circuit, if you disturbed it look at what you disturbed, if you didn't then check voltages against schematic and report back with a comparison and we can help you interpret.

zeno · #57 03-09-2023, 07:38 AM

Check the service / normal switch first. It often gets bumped or dirty.
See how the CRT looks after set-up. If the blue looks bad you
can do a clean & balance to perk things up. I wouldnt go to
a full rejuve.

73 Zeno

LFOD !

Lain94 · #58 03-19-2023, 02:35 PM

Ok, it looks like it was just a loose connection and I made sure all connections were secured this time. Vertical deflection is back. I tried my best to fine tune the rf signal i was getting from the digital to analog converter box. Also adjusted AGC, Contrast, brightness, horizontal sync, vertical sync ect. I also used my color king test pattern generator.

Based on the photos the convergence is way off and possibly color purity as well. But the most important issue to fix is the weird multiple images that seem to occur along the horizontal.

I am going to check the horizontal sweep frequency later with my oscilloscope and see that the horizontal sweep is at 15.75khz.

I suspect leaky caps in the horizontal circuit possibly. As for the lack of green color. This was later found to be a simple issue with the green video driver pot. on the drive board. It is just a bit finicky and I forgot to clean those. So green does work just did not realize the issue with that until photos were already taken.

https://imgur.com/a/ZcWcEWl

Electronic M · #59 03-19-2023, 04:51 PM

Pro tip for adjusting horizontal frequency with a scope: first scope composite video from a DVD player or other precise stable signal source, set the horizontal time axis of the scope for 2-3 horizontal sync pulses on screen (from this point on don't touch the time scale of the scope), count the divisions between leading edges of pulse tips, then hook the scope to the TV and adjust the TVs horizontal osc coil (hold pot centered if present) so the number of divisions between peaks is the same number counted with no signal applied to the TVs tuner...When you connect signal it should be locked without having to touch any controls after doing that.

Lain94 · #60 03-20-2023, 01:34 PM

Also, should I be wary of whether or not the oscilloscope can handle the high voltages in the horizontal sweep circuit? This oscilloscope is one of those digital chinese ones you can get for around 100-150 bucks. I just did not want to fry the oscilloscope by feeding it voltages far higher than what it may be designed for. The model of this Oscilloscope is ADS1014D. The manual says it can handle up to 400V voltage continuous which is far lower then what voltages are likely to be encounterd in the horizontal circuit.