Packard Bell Color TV

[bhegges]

I would like to share my current project, a Packard Bell 1968 color TV, model CQ-956. The TV was purchased and remained here locally with it currently belonging to the original owner's grandson. Searching old ads would suggest this TV cost $599 ($4,500 in today's money).

Most of my project are old radios but this TV was too nice to not bring home, I have fended off several comments to convert it into a fish tank. My goal is to get it working to play old games, catching local TV news, and maybe some movies, probably 1 - 4 hours runtime per week.





I have so far replaced all of the electrolytic capacitors and swapped out the tubes with a set of NOS and/or tested good tubes (maybe unnecessarily). For now I am feeding signal in on channel 3 or 4 via a NES game console. Once powered on I get sound and picture, this is a very good start as there could have been countless issues to fix just to get to this point.

Now the picture is dim, fuzzy, and only displays black and white. High voltage measures about 26K which is a bit high and the big issue is after 5 minutes the high voltage cage starts to make a hissing noise, the horizontal tube starts to glow red, and then the internal breaker trips out. I do have a thread open on the Antique Radios forum and was suggested to look at some of the coupling capacitors feeding the horizontal output circuit. I am currently working on this along with sourcing two amperage meters to monitor and set the horizontal sweep circuits. My fear is that the issue is a failing flyback transformer.

I have replaced C166, C167, and C114. R204 measured 40% high so it will get replaced. Also R212 & R214 both measured high while R213 was open. The HV pot was turned all the way down which makes sense R212 & 214 measured high. Fixing this should help to adjust the HV within range. Once I get all of these parts replaced I will report back.

[Electronic M]

Once you get those parts in I would recommend temporarily removing the HV cage door, running the set over 5 min in a very dimly lit room and trying to locate the exact point of the hiss. The hiss is probably corona (the HV discharge not the virus) or arcing. HV cages collect dirt like a magnet and dirt can be conductive. Cleaning with isopropyl (rubbing) alcohol and glass cleaner will help. Some sets had a rubber insulation tire on the flyback and those sometimes become somewhat conductive and have to be peeled off and replaced with sensor safe silicone...Shango66 on youtube has some good vids on the topic (on RCA CTC17 sets IIRC).

EDIT: I'd also measure the 1000V and 800V boost supplies. Knowing if they are below (excessive load on flyback or insufficient drive), within 10% of rated( normal), or high (under loaded or overdriven) as well as control and screen grid voltages on the output tube usually gives a pretty accurate picture of where in the horizontal circuit the problem(s) lurk.
If your DMM can only read 600V (common limitation) you can get around it with this clever trick (came up with it on the spot while servicing a console in the owners home with limited equipment)...Connect meter neg to ground and measure a B+ rail in the 400-500V neighborhood and write down it's value, then connect meter negative to that B+rail you just checked and the positive meter terminal to B+ boost and add the noted value to your meter reading to get the actual boost voltage. The difference between a 450V rail and the 1KV boost rail is only 550V so a meter rated for 600V max can safely measure it.

First priority should be a good stable horizontal circuit, followed by focus, then anything needed to make the monochrome picture optimal, then fixing the color.

[Notimetolooz]

Nice save!
I was going to suggest looking inside the HV cage in darkness also.
If the HV is lower after replacing the parts you might have solved that breakdown/corona problem. If you use several cleaners in sequence you should end with alcohol, that will remove any left over moisture.
BTW, this is why only replacing the old tubes that test bad should be replaced. You could cook a brand new tube if there is a circuit fault.
You are making a big step going from radios to a color TV. This could be a long road. Do you have a color pattern generator? You may need one to adjust the convergence and color balance.
Fixing the HV first is a good call (assuming the main supply voltages are good), the regulation of the HV is important to get the image correct. In a B/W set small changes in the anode voltage don't effect the picture noticeably, but it does in a color set.

[AlanInSitges]

I love those PB sets! Built like a Zenith with a fold-out chassis, kind of the best of both worlds. I always thought they had very dowdy control panels though.

It would be interesting to know if the HO tube still redplates after replacing those two capacitors, and what the voltage is on pins 2-6.

[bhegges]

I got parts in today and made several changes. Maybe not the best way to troubleshoot as it's hard to tell what change affected what, but see below for the changes made since the initial noted hissing, redplating on the horizontal output tube, and tripping the breaker:

• Replaced the horizontal output tube as I am not sure of it's state now
• Replaced the HV rectifier as it was glowing blue, i.e. a gassy tube
• Replaced C166, C167, C114
• Replaced R204
• Replaced R212, R214, R213 with HV resistors and centered the HV adjust pot
• Hooked up meters for testing

I installed the chassis and tried again but unfortunately tripped out the breaker. here are my notes:

• At no time did the horizontal output tube glow red
• I had the lights off several times while running and as the HV cage area started to hiss but I could not see any arcing
• The horizontal output tube current first measured at 235ma so I turned down the horizontal efficiency to bring it just under 225ma
• On the second try I remembered to hook up my DMM to measure the horizontal output grid voltage on pin 2 & 6, it measured at -56v while the schematic specs only -46v
• On the second try the horizontal output tube current measured at about 125ma, I didn't make any adjustments this time so I am not sure why it was lower
• HV measured at 24k volts on the first try and 23K volts on the second try
• I let the set cool for 30 min and tried a third test, this time the horizontal output tube current measured approx 50ma but had -68v on the grid, adjusting the horizontal efficiency didn't affect anything so I turned the set off and am at a stopping point
• I just now seen Tom's edit about checking the 1000V and 800V boost supplies so I will have to go back later and check these.

As for the picture after some fiddling with vertical control I could get a steady readable picture, it is still only B/W and blurry. I will have to look into why the horizontal output grid voltage is running 10+ volts too negative. Would this cause something to heat up, cause the high voltage hissing noise, and trip the breaker or would the symptoms point to a second issue to fix, I am open to your thoughts.

[bhegges]

Attaching the horizontal multiplier circuit for further reference:

[old_tv_nut]

MULT here stands for multivibrator (oscillator).

[Electronic M]

So you definitely have drive. It is curious that it is giving a more negative grid voltage but it is a less dangerous issue than the grid being less negative.
Horizontal output screen grid(pins 1-7) and boost are important to know. If screen is high it means the flyback is drawing too much current, if it is low it means the flyback is drawing too little current (and cathode emission is being absorbed primarily by the screen grid which is bad for the tube).

When diagnosing horizontal knowing that the grid is not too positive tells you the osc is working, and the screen grid and boost voltages are the more important for troubleshooting.

If you can't see the hiss you could find it by ear...get a few feet of small plastic or rubber tube or hose. Hold one end of the hose to your ear and move the other one around in the HV cage like a stethoscope and listen for the loudest hiss.
Sometimes sets develop HV breakdown in strange places ...a friend brought me a tube color 13" Zenith once that the screw that held the HV rect socket to the insulator cup had arced through the bottom of the cup to the chassis. You couldn't see the arcing but it was loud enough to find. Had to drill out the carbon tracked plastic, fill it with silicone and shorten the screw to repair the issue.

[bhegges]

I have had a very busy weekend so far. One exiting thing was I found a 1969 Packard Bell parts TV. This was a top of the line TV/Stereo console set, model CP 984. The TV is non-working, some examination shows a burnt wire in the yoke coil. It has a different chassis with a lower tube count (more solid state components) but does share some common parts to include the fly back transformer which had been replaced at some point.



I also had found on eBay NOS high voltage sockets for the high voltage rectifier & focus rectifier tubes and plate caps with 30K wire for the horizontal output and shunt regulator tubes. I thought lets eliminate all sources of possible HV leaking. Finally I picked up some additional meters for testing. While the chassis was on the bench I did jumper the circuit break to test. I used a variac hooked up to a hair dryer and found that slowly turning up the voltage the breaker trips at about 3.5 amps.

So after installing a different flyback transformer, sockets, and plate caps with associated HV wire I got the chassis back inside the TV along with lots of meters to monitor things, here are my testing notes:

• TV draws 2.8 amps from the AC line
• Horizontal output current dialed in at 220ma
• HV adjusted to 23K volts
• Reading -51 volts on the horizontal output tube grid vs -46 per the schematic
• 0.850ma shunt regulator tube cathode current, spec states should be at or above 0.850ma
• After about 5 min the shunt regulator tube cathode current started climbing up to at least 1.2ma, shortly after this I got visible/audible sparks from the shunt regulator tube plate cap, I then cut the power
• I repeated this for a second time, all measured good and again the shunt regulator tube cathode current started to climb, I believe I could start to hear some hiss so I turned off the TV
• I feel like I either fixed one problem and now am on the next, or I increased the difficulty for HV to leak and now fails more visibility
• At no point did the breaker trip, but I was watching and cut the power likely ahead of the breaker tripping

As I look at the shunt regulator circuit there are not too many parts. I have already replaced C114, but I just now measured R215 which calls for a 1000 ohms, 5% resistor. It measures high at 1,164 ohms (16% off), could this be the issue, or could it be further changing value as it heats up?

The other concerns it around the cap I used to replace C114, I was able to match the temp code from one of the replacement parts noted from the SAMS document so I hope I am ok here.

[Notimetolooz]

A resistor that is changing value may very well be the problem.
To bad you didn't monitor the HV during the time the shunt tube current was rising. Voltage breakdown at the cap would point to the HV moving higher.
I don't see that you said that you replaced the shunt regulator tube, that may be another possibility.
Kind of odd that the shunt current rises yet the HV is still climbing.
Sounds like the flyback is over producing.

[bhegges]

Update: I finished replacing resistors and capacitors that measured bad in the horizontal and high voltage circuits. I have replaced all of the high voltage tube sockets as there may have been a possible HV shorting issue. I also added a 250ma fuse to the horizontal output tube.

The TV starts up, I get audio and the screen lights up but as before the horizontal output tube current slowly rises and eventually pops the fuse. I tried several times to fiddle with the horizontal hold and horizontal efficiency but in all cases I could not get the picture to hold and eventually the horizontal output fuse would blow. The HV does rise starting at 23k volts up to about 25k volts before the fuse blows.

Any ideas or what to check next for why the horizontal output current rises?

Voltage measurements:

• 23-25k HV source set and initially measured 23k volts
• 390v source measured 409 volts
• 275v source measured 312 volts
• 1000 boost measured 871 volts
• 810v boost measured 819 volts
• -46v Horizontal Output tube grid (pin 2,6) measures -50.6 volts

TV image:

[old_tv_nut]

If the horizontal frequency is running lower and lower with time, that could raise the current draw.
I would work on getting the horizontal sync good first.

I missed whether you checked X14 (dual diode AFC detector) or not.

Do you have a scope to check waveforms vs. the schematic?

[Electronic M]

Originally Posted by old_tv_nut

If the horizontal frequency is running lower and lower with time, that could raise the current draw.
I would work on getting the horizontal sync good first.

I missed whether you checked X14 (dual diode AFC detector) or not.

Do you have a scope to check waveforms vs. the schematic?

+1
A horizontal osc running reliably on the correct frequency to achieve sync is the key stone of the horizontal opperation... without that you will end up chasing your tail trying to solve problems the Osc causes elsewhere.

[nasadowsk]

I'm also a bit suspicious about that 1k boost..

[bhegges]

I am not sure what exact part fixed the rising horizontal output tube current but a combination of the following let me run the TV for 30 min, after which I turned it off. Here is what I fixed:

• Replaced all of the parts from the horizontal osc. plate to the horizontal output grid
• Replaced the horizontal osc tube with a NOS tested tube
• Replaced the boost rectifier and C119 capacitor which brought up the 1000v boost to a measured 1020 volts, thank you Zeno, I did use a NOS ECG 119 selenium rectifier
• Replaced the horizontal AFC diodes
• Replaced the remaining film capacitors located on the bottom chassis, note I still need to go through the other circuits

One remaining concern - the horizontal sweep circuit adjustment recommended adjusting the horizontal efficiency coil to keep the horizontal output tube current under 225ma. When adjusting the horizonal hold to get a stable picture the horizontal output tube current ran at 240ma. Are there other settings or other parts to check so I can bring the current down. I suspect the horizontal output tube and flyback transformer will not like running hot long term.

NES source, playing Legend of Zelda: