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  #31  
Old 08-08-2013, 10:25 PM
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TinCanAlley TinCanAlley is offline
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Quote:
Originally Posted by marty59 View Post
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.
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  #32  
Old 08-09-2013, 04:00 PM
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Quote:
Originally Posted by TinCanAlley View Post
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.
Not to worry. I only used a gun to do filter cans & the grouned
lug of terminal strips. A pencil with the hottest tip will work on
the other lugs. We used the common weller station.
Alternative is snip off one end to test then tack back on
if OK. I always replace into the lug to keep it looking
neat & save time but thats just me.
BTW I dont know if its come up but the ground lugs on
Zeniths break off sometimes & go int. Poke each one with a
small screwdriver & resolder any that crack open.

73 Zeno
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  #33  
Old 08-09-2013, 05:42 PM
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ditto those ground connections on zenith term strips, esp happens after you have been tugging and flexing them a lot.

you can check that diode in circuit somewhat. both sides go to the power supply, but thru some rather high resistance so you should be able to get a front to back measurement to at least see some change when testing.
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  #34  
Old 08-09-2013, 05:52 PM
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CR 201 on the schematic
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  #35  
Old 08-09-2013, 08:08 PM
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Quote:
Originally Posted by DaveWM View Post
CR 201 on the schematic
I wish the Photfacts scans were clearer. If I'm counting correctly, I believe CR201 is across pins 11 and 12. I'm attaching a pic of what I think it is. I can also post a pic of the entire section of the underside if you like.

Does anyone else think it looks like it was either replaced before, or someone already cut one lead, tested it and then soldered it back together?
Attached Images
File Type: jpg CR201 Small.jpg (91.9 KB, 14 views)
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Last edited by TinCanAlley; 08-09-2013 at 08:16 PM.
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  #36  
Old 08-10-2013, 07:05 AM
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Looks like it was snipped but not changed.

73 Zeno
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  #37  
Old 08-10-2013, 08:11 AM
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I am looking at the zenith factory schematic, so the numbers could be different from the sams, but that looks right. you can check that diode, the 33k and if you look further back there should be a couple 100k 5% resistors. Interesting that its already been snipped and soldered back.
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  #38  
Old 08-10-2013, 08:15 AM
DaveWM DaveWM is offline
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the sams should show a 20v pp blanking pulse at the base AND emitter of the blanking amp transistor at the horz rate.

if bad this looks like the replacement

http://www.nteinc.com/specs/500to599/pdf/nte506.pdf

Last edited by DaveWM; 08-10-2013 at 08:24 AM.
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  #39  
Old 08-10-2013, 08:29 AM
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you could also check the bias voltages at the blanking transistor (if the blanking pulse is incorrect per the scope). If the diode is good and the fly pulse is getting to the base of the transistor BUT the bias is incorrect, that would effect the gain of the transistor and upset the output at the emitter. The sams shows the pulses at both the base and emitter (which look the same) I presume to check that the transistor is working properly (if not it would be a defective transistor OR incorrect bias).
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  #40  
Old 08-10-2013, 11:35 AM
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Forgive my ignorance, but the transistor (Q202) is clear on the other side of the chassis from the circuits we're looking at. Is that because the pulse is coming off the horizontal module, going through these circuits and then traveling cross to the other side of the chassis to the transistor? I'm getting better at reading schematics and wish they were to scale. LOL

Anyway, I've managed to locate just about all the pieces and will talk with my brother tomorrow about setting up a day for him to come by with his equipment so we can do some serious testing.

Last question... Where are you seeing the pulse from that circuit? I'm looking at Photofacts and there isn't one for the emitter, but is one for the base which is shared with the collector of the vertical blanking. Strange thing is, there are two different patterns for the same test point. Both are 18V and then they differ with numbers I can't figure out. One graph is 30 and the other is 7875 (both numbers followed with a little curved line that looks like an oversized tilde). They both are different wave forms. No clue as to what those numbers are trying to tell me.

Thanks
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  #41  
Old 08-10-2013, 12:23 PM
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the two rates are the vert and horz (30 and 7865) these are for setting up the scope sweep speed.

I am looking at a factory manual, the scope readings do not match up, with the sams so can't really help. So you are back to checking for a pulse (should be two a vert rate pulse and a horz rate pulse both are for blanking.

you can trace the pulse from the flyback (should be pretty big at the horz rate, like 200v pp) thru a cap (.0047) thru the resistor (33k) thru the diode all the way to the transistor, and then see it at the emitter.

The best way to know for sure is to have a working set to compare to, but I realize that is not something that you have.

I would check the diode (easy since its already been clipped), and the transistor (again easy since it's socketed). if they check use the scope and see if you get both horz and vert blanking.
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  #42  
Old 08-10-2013, 01:08 PM
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TinCanAlley TinCanAlley is offline
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Quote:
Originally Posted by DaveWM View Post
the two rates are the vert and horz (30 and 7865) these are for setting up the scope sweep speed.

I am looking at a factory manual, the scope readings do not match up, with the sams so can't really help. So you are back to checking for a pulse (should be two a vert rate pulse and a horz rate pulse both are for blanking.

you can trace the pulse from the flyback (should be pretty big at the horz rate, like 200v pp) thru a cap (.0047) thru the resistor (33k) thru the diode all the way to the transistor, and then see it at the emitter.

The best way to know for sure is to have a working set to compare to, but I realize that is not something that you have.

I would check the diode (easy since its already been clipped), and the transistor (again easy since it's socketed). if they check use the scope and see if you get both horz and vert blanking.
Okay, here's a pretty simple question about testing transistors. If I have an NPN and clip the positive lead to the base, should I set my meter to diode or 20M? When set to diode and test a transistor I have just sitting around, I get about the same numbers (580 - 620) on the base and collector. If I set it for 20M, I get 2.45 and 10.38.
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  #43  
Old 08-10-2013, 05:34 PM
DaveWM DaveWM is offline
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diode check base to collector check it like a diode
diode check base to emitter check it like a diode
Ohm check emitter to collector should read open both ways (switch leads).

if if doubt just do a you tube search on checking transistors with DVM there are plenty of demos.

I use a analog meter that has a built in reversing switch in the resistance mode.
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  #44  
Old 08-10-2013, 07:06 PM
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Quote:
Originally Posted by DaveWM View Post
diode check base to collector check it like a diode
diode check base to emitter check it like a diode
Ohm check emitter to collector should read open both ways (switch leads).

if if doubt just do a you tube search on checking transistors with DVM there are plenty of demos.

I use a analog meter that has a built in reversing switch in the resistance mode.
Got it. So now I must wonder why the transistor I replaced on the NOS horizontal board doesn't work in the board, but checks out good when tested. I've gone back and forth with it a few times in the board and it sure doesn't work. The transistor from the old horizontal board works perfectly.

I know I'll get it. I've made quite a bit of progress and gained quite a bit of knowledge in the past month.

Thanks
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  #45  
Old 08-10-2013, 07:27 PM
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Originally Posted by TinCanAlley View Post
Got it. So now I must wonder why the transistor I replaced on the NOS horizontal board doesn't work in the board, but checks out good when tested. I've gone back and forth with it a few times in the board and it sure doesn't work. The transistor from the old horizontal board works perfectly.

I know I'll get it. I've made quite a bit of progress and gained quite a bit of knowledge in the past month.

Thanks
IF a transistor works in one board and not in the other in the same location, I would say the transistor is ok, I am a little confused on this, make sure you are testing correctly reverse the E to C leads, should read open both ways

BC open one way, low resistance when leads reversed.
BE open one way, low resistance when leads reversed.

you need to make sure you are doing this right. But I dont really understand why you are futzing around with the horz board. Check the diode in the blanking circuit.
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