Are These Circuit Traces Bad

[TinCanAlley]

Originally Posted by DaveWM

you need to deal with one problem at a time.

sounds like some kind of interference, make sure you are not setting a RF source near the set (like a DVD player on top of the tv) try a different signal source, double check that you have everything hooked up right (300ohm to 75 ohm balun) make sure you have not messed up lead dress inside the tv (crt wires, HV wires,tuner IF link). All grounds are in place.

Shot gun repairs often introduce new problems making diagnosis a more difficult problem. don't take it personally, a lot of peeps seem to think replacing every cap in sight will fix everything. It has been my exp that most sets from the mid sixties on do NOT require a lot of cap replacement, and doing so just introduces possible new problems.

So on to the existing problem without a scope its just a guess that the horz blanking is a problem causing the jail bars. if you have the schematic you should be able to find the diode that feeds the pulse to the blanking transistor. I do not know if its on a modual or chassis mounted. On the 25DC56 its NOT on the modual.

I see a few things marked with "blanking." I'm attaching some pics of a basic circuit layout that might be what you're referring to. If it's there, point it out and I should then know where to look on the schematic. Also attaching a pic of a pin with a label regarding raster blanking. Not sure what that is, but the lead is headed over towards the tuner wiring.

[DaveWM]

Q202 is the one, you could try checking it, but I doubt its the problem. under the chassis you should see diode that goes to the base of that, then a couple resistors 33k then a couple 100k (5%). from there it goes to the flyback thru a cap.

I would check the transistor, diode,and resistors. Pretty sure you will need to take them out of the circuit to check, which will be a PITA and of course they may be ok. With out a scope you are handicapped into doing work to check things rather than just looking at the signal.

Again this is only a guess, so don't expect it to fix things its just an educated guess.

If I were you I would start looking into buying a scope, I know there will be some that say its a waste of money, true you can fix a lot of stuff without one, but when you run into tough dogs, it will save time, "don't be a dope, use that scope"

[DaveWM]

oh in case you do not know, its always wise to use heat sinks when soldering semiconductors, esp old ones that may be germainium. I use hemostats. clamp near the body of the part to sink out heat from the leads when soldering our un soldering.

[TinCanAlley]

Originally Posted by DaveWM

oh in case you do not know, its always wise to use heat sinks when soldering semiconductors, esp old ones that may be germainium. I use hemostats. clamp near the body of the part to sink out heat from the leads when soldering our un soldering.

I've been using a pair of needle nose. They act as a heat sink and allow me to wiggle the lead loose and such.

[TinCanAlley]

Originally Posted by DaveWM

Q202 is the one, you could try checking it, but I doubt its the problem. under the chassis you should see diode that goes to the base of that, then a couple resistors 33k then a couple 100k (5%). from there it goes to the flyback thru a cap.

I would check the transistor, diode,and resistors. Pretty sure you will need to take them out of the circuit to check, which will be a PITA and of course they may be ok. With out a scope you are handicapped into doing work to check things rather than just looking at the signal.

Again this is only a guess, so don't expect it to fix things its just an educated guess.

If I were you I would start looking into buying a scope, I know there will be some that say its a waste of money, true you can fix a lot of stuff without one, but when you run into tough dogs, it will save time, "don't be a dope, use that scope"

My brother has a scope I could borrow on Sunday. If I got that, could testing be something I could be stepped though (where to hook up, what to set it for and what to expect)?

[DaveWM]

not really, using a scope takes some experience, and knowing what to look for.
Besides just knowing how to set it up takes practice. It would be a good learning exp, but may not be enough to point to the problem. This is why you need to get used to using one a lot, the more exp you have with it the better.

[TinCanAlley]

Okay, I found the transistor socket on the bottom side of the chassis. I found a 1K resistor from the socket. I'm trying to trace where it goes from there. I think I'll need a more powerful soldering gun. The hollow end of the pins are filled with solder and the ends are stuck inside. My 35w can't melt the solder as the pin and such are pulling the heat away.

Time to make a list of things to purchase.

Oh, my brother knows how to use the scope (he fixes old B&W sets), so I'll try and borrow him along with the scope.

[DaveWM]

don't forget the heat sink, a lot of heat can damage a part before you get to check it. Those zenith solder pots can be difficult to deal with, I could get things out but getting back in was not so easy. Try cleaning the outside of the pot, then a little flux to get the heat to transfer well. use the sink I use it even on resistors, no reason to get them so hot.

[DaveWM]

Hopefully the schematic will have some scope patterns for that transistor to look at. without that it may not be much help. My DC56 has a pattern showing a pretty strong vert pulse with smaller horz pulses at the output from the blanker (emitter i think).

[marty59]

Originally Posted by TinCanAlley

Okay, I found the transistor socket on the bottom side of the chassis. I found a 1K resistor from the socket. I'm trying to trace where it goes from there. I think I'll need a more powerful soldering gun. The hollow end of the pins are filled with solder and the ends are stuck inside. My 35w can't melt the solder as the pin and such are pulling the heat away.

Time to make a list of things to purchase.

Oh, my brother knows how to use the scope (he fixes old B&W sets), so I'll try and borrow him along with the scope.

With those Zenith terminal strips, if that connection point is not only filled with solder but has a bunch of leads attached sometimes the best thing to do is cut the component out and "J" hook the new one in as opposed to the possibility of heat damage by using a bigger iron.

A scope can be handy as mentioned. Years ago I had a Zenith 24MC32 that had three "very transparent" vertical bars running through it and they were not always noticable. There was no sweep distortion so I believed it had to be in the video somewhere. I was still quite the novice back then so I lived with 'em...

Sounds like your brother may be handy too!

[TinCanAlley]

Originally Posted by marty59

With those Zenith terminal strips, if that connection point is not only filled with solder but has a bunch of leads attached sometimes the best thing to do is cut the component out and "J" hook the new one in as opposed to the possibility of heat damage by using a bigger iron.

A scope can be handy as mentioned. Years ago I had a Zenith 24MC32 that had three "very transparent" vertical bars running through it and they were not always noticable. There was no sweep distortion so I believed it had to be in the video somewhere. I was still quite the novice back then so I lived with 'em...

Sounds like your brother may be handy too!

Thing is, I have to lift one end to remove it from the circuit for testing. I think I'll go the scope route and if that doesn't work, I'll live with the bars. I can see myself doing more damage if I start poking around with a big soldering gun.