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  #1  
Old 11-20-2010, 06:06 PM
DaveWM DaveWM is offline
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Packard Bell console

NOS set, only two issues, vert height (50uf cap in vert circuit) and no sync (horz and vert).

the vert was easy, the sync turned into a tough dog. its a hybrid (IF/sync transistor, all the rest tube). after chasing my tail for a few days I finally checked the bias pot on the noise inverter. I cant recall if i checked this early on (its a 100 ohm trim pot) but even if I did I think I may have been misled due to its connection to a transistor in the circuit (dont recall if I swapped the meter leads). needless to say after days of putzing around I finally managed check it again. I had noticed the adj of that pot had confusing results on the scope of the sync pulse, still did not dawn on me. I think I may have been too deep into it (forest for the trees....) Anyway after a good rest I check there again and found it open. This would totally screw the bias of the noise inverter transistor and I assume it was cutting off the sync completely. A trip to the surplus store resulted in a very nice precision pot (overkill but it was the only small 100ohm pot they had). A little micro surgery to remove the old and replace with this (all in the same location so adj is easy to get at), on the PCB (there are 3 trim pots on a single board).

finally after days, and countless pulling of the chassis, I plug in and get a perfect lock. I also now see what it should have looked like all along (the sync pulse that is).

I still need to check the cathode current but other than that I can stick a fork in it. I will get a pic later.

One other thing, its a remote set, so I will be looking for a clicker for it.
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  #2  
Old 11-20-2010, 06:23 PM
DaveWM DaveWM is offline
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pics
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File Type: jpg chassis.jpg (68.9 KB, 63 views)
File Type: jpg new pot.jpg (40.9 KB, 47 views)
File Type: jpg screen pic.jpg (39.3 KB, 67 views)
File Type: jpg screen pic1.jpg (26.9 KB, 54 views)
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  #3  
Old 11-20-2010, 06:35 PM
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sampson159 sampson159 is offline
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what kind of crt is in this set?looks amazing.
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  #4  
Old 11-20-2010, 06:49 PM
DaveWM DaveWM is offline
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25AXP22

bit of a halo but not bad in a darkened room. Has a degauss button on the front, cool stuff
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File Type: jpg cabinet front.jpg (43.0 KB, 65 views)
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  #5  
Old 11-20-2010, 08:08 PM
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Findm-Keepm Findm-Keepm is offline
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Quote:
Originally Posted by DaveWM View Post
A trip to the surplus store.....
Skycraft? I've always wanted to visit there - never enough time with the Disney trips we've made.

Cheers,
__________________
Brian
"Capacitor Cosmetologist since 1979"

When fuses go to work, they quit.
Make Safety your first thought, not your last.
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  #6  
Old 11-20-2010, 09:45 PM
DaveWM DaveWM is offline
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aka skyjunk, I go there about once a week.

Next time you are in town, let me know you can check out the collection, I am close to disney
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  #7  
Old 11-21-2010, 02:43 AM
ctc17 ctc17 is offline
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The packard bells had either Zenith or RCA crts. By the eia number. This one looks like a Zenith having the green halo. The chassis is about 80% an RCA CTC17-35 clone with lots of mods to make servicing much easier.
They are ok sets they just always seem to develop bizarre time sucking problems like this.
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  #8  
Old 11-21-2010, 03:52 AM
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Eric H Eric H is offline
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Nice looking color on that set, I wouldn't have expected as much from a PB.
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  #9  
Old 11-21-2010, 06:29 AM
DaveWM DaveWM is offline
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like CTC17 said, engineered to make service easy. lots of little things, like plugs to disconnect the tuner/control panels, very easy chassis to set on the bench (can flip it upside down, the HV cage and part of the vert chassis makes a perfect stand) plugs that connect the filter cans (easy to take them out of circuit to check for leakage of the cap). IF section on a PCB but all the tubes are handwired so no PCB damage from tube heat. focus tube rather than Se rectifier, jumper provided for cathode current checks, all the tubes are easy to get at, just a lot of stuff like that. The only real weak point was the cheap adj pot board that failed. I guess from an enginneering stand point it makes since (the pots are not supposed to see any cycling), and I can't figure how it failed the way it did. the pot did not just have a bad spot, but rather the conductive part seemed to be just gone across 90% of the arc.
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  #10  
Old 11-21-2010, 09:26 AM
DaveWM DaveWM is offline
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decided to check the cat current at reduced line voltages.

I put the set on a variac and dropped it to 105vac, cathode current on the HOT went to 180ma from 220ma with no change in HV (shunt prob just not working as hard) and no change in vert/horz size (compensation parts like VDR's and other bias componets prob accounting for that).

bottom line is I think this set was engineered to work at lower line voltages, with higher voltages just generating more heat. I suppose this is a trade off on designs that did not include power supply voltage regulation.

You can bet I will be using a variac to run this set. I kicked around an idea adding some resistance to the screen resistor on the HOT, set it up to operate at 120v and still get the lower HOT current. Not sure if I want to go adding circuitry. It would be nice if I could engineer in a jumper that would switch in a voltage drop, I will have to look over the chassis for this. I would prefer to make min changes in the orig design. A bucking transformer would be good but these old sets pull a lot of power, not sure how to size that.
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Old 11-21-2010, 09:38 AM
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It's a long shot, but check the power transformer for a high line voltage tap. Most RCA color sets had such a tap, and some even had a normal/high switch.
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  #12  
Old 11-22-2010, 09:07 AM
DaveWM DaveWM is offline
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Back to it, after watching some other programming I seem to have a vert linearity issue, not unlike what CTC17 has been fighting on a RCA with a like circuit.

The only clue I have is the vert drive to the vert output of the 6FG7 is low, 200v PP vs 270vPP. Upping the boost supplied plate voltage (by reducing the resistance thru the dropping resistor from the vert height resistor) increases the grid drive, and give more vert deflection, enough to work with (right not the vert height pot is maxed out, and the lin pot is used to just fill in the screen but results in a egg shaped linearity problem).

the is not wavefore given for the plate of the multivibrator, the grid drive to the multivibrator is correct (160v PP). the grid bias amount was measured with a VTVM and was correct -38v at that point.

From what I have read about multivibrators, the RC network feed back is fairly critical to shape the wavform that starts as a pulse from the vert output. I am starting to wonder if the problem lies there, that is the biasing being done by the linearity pot is not the problem, but is trying to compensate for a defective wave form from the mutivibrator.

Or to put it more directly the height is fine, its the shape of the drive that is the problem, I will take another look at that shape.


in this set the linearity pot is connected to the grid of the vert out.

I am just not checked out enough on the complexites of the RC feedback loop to know exactly where to look, but there are a few precison caps and resistors in that chain that I will start with.
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  #13  
Old 12-03-2010, 07:32 PM
DaveWM DaveWM is offline
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did some more work on it, replaced some caps in the vert circuit, replaced a out of spec resistor in the vert height, and subbed some tubes. Not sure of the cause or cure, but its working great now, very good linearity, full height.

there is a flakey tube socket in the chroma section but I dont feel the need to replace the socket just yet.

I need to find a two channel clicker to see if the remote works, I can get action with the jingle keys trick so I know its doing something. I tried a maggie phantom remote, no joy.

HOT cat current is just a bit over 200ma, the shunt tube is 1ma, purity and convergence very good. HV 25kv at min brightness

I just finished buttoning it up, so will park it for now and move on to the next project.
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  #14  
Old 12-03-2010, 08:24 PM
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Glad you got it going! That set looks similar to the '67 model that I got from that TV shop in SC. I think mine is all tube and is all handwired. The main issues with mine are color problems and a bad cataract. As far as a remote for yours, it's possible that a Zenith clicker remote will operate your set.
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  #15  
Old 12-03-2010, 08:43 PM
DaveWM DaveWM is offline
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yea i was thinking a zenith clicker may work.

whats the color issues you have on yours?
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