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#916
11-01-2022, 06:34 PM
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Right now I’m not going to plug this in until I can find C3-C capacitor to see where it goes because according to the Motorola schematic the L42 should only have 500v on it but I’m testing it has around 780v so I need to find where this cap goes maybe I placed it in the wrong place. This extra voltage on the L42 is not good I need to find out why.
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#917
11-01-2022, 06:47 PM
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Quote:
 the Motorola schematic is referring to the tie points on the flyback transformer, It's saying + and - 500v PP as in Peak to peak, that is not to be read as DC voltage ref to ground. stick with the SAMs. It's less confusing! 
__________________
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#918
11-01-2022, 06:51 PM
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That Motorola schematic has some good additional information on it.... It would be cool
to know if those voltages are there, and correct. I was wondering if the focus voltage is correct, and in the range that is printed on the Sams.... Can you turn the focus coil and have a range of 4.3KV to 5.2KV ? I know with a HV Probe you will not see much resolution, but it may tell you if things are OK enough to not worry about that part of the circuit. Not sure how you would check that Plus & Minus 500V P-P - I guess you can give it a try with DVM and see what happens...... Also for L42 getting hot, you know each coil & Cap are a tuned circuit, If there is something wrong, it may be peaking at a poor point and creating too much power. All I can think of right now would be to check focus voltage as best you can. Since the flyback was removed, it may be a good idea to try and see as best you can that the pins that go where you think they go have the right resistance on them as best as you can determine. Take a picture, several pictures, of the flyback wiring, then disconnect all the wires, measure the resistance of all the pins as you see them using both schematics, and try and determine if it's wired correctly. You may also want to check resistance from one isolated winding to another, This confirms no short between windings and that they are wired correctly inside the transformer.... Since you have 2 Flyback transformers, you can compare between the two..... My thinking is that since that flyback has pins that are tied to components and then back to other parts of the flyback, that if a wire is not connected right, then voltage may be fed to, or from one section out of phase, and causing problems, possibly even heat on L42. Does the flyback run hot? I'm not sure I would switch any wires unless you have real good cause to do so, you don't want to make anything worse.... With that coil measuring a higher resistance, it may be because it's been hot, and starting to change because of that.... Or since there are differences on the resistance measurements of some coils from one schematic to the other, it may just me differences in their test equipment, or component tolerances..... .
__________________
Yes you can call me "Squirrel boy"
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#919
11-01-2022, 07:15 PM
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Quote:
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#920
11-02-2022, 07:46 AM
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The focus voltage is perfect and adjustable to sams specs. But the 6hs8 v6 has questionable voltages on 3 and 6 3 should be 2.5v but it’s only .3v and 6 should be 145v but it’s 111v and these pins have the 470pf and the 2.2pf caps these I think are for feedback and it don’t look like it’s doing anything otherwise the agc would probably work and I would have video. I question this because both caps have a wire one to L42 and the other to the focus coil so if these caps are not conducting in the circuit this could be affecting L42 and killing the video it’s all tied together.
Last edited by timmy; 11-02-2022 at 08:04 AM.
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#921
11-02-2022, 08:44 AM
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You ran the 0v-9v volt sweep at test point A to show that it's not an AGC problem with the video, otherwise you would have seen a reaction on the screen as the voltage was changed at point A, and the gain was forced to change.
You said that you unhooked C59/C60 and there was no change in the heating of L42, so unless perhaps there is a fault in the wires between C59/C60 and the area of the flyback transformer /L42, the problem is still in the area of the FBT. R13 alters the bias on pin 7 of V6 and R14 alters the bias on pin 6 V6, the balance of the 2 will alter the voltage on pin 3. What you uncovered the other week, you do have an IF fault, regardless of if AGC is working correctly or not, 3rd IF is working, direct into 2nd IF works, but 1st does not, including L4 . This has yet to be debugged.
__________________
=^-^= Yasashii yoru ni hitori utau uta. Asu wa kimi to utaou. Yume no tsubasa ni notte. いとおしい人のために
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#923
11-02-2022, 09:34 AM
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So these need to be closely checked, if they have not been already.
R62/R88/R91/R85/R87/R14 C60 side of R87 should be easy to test, resistance to gnd, 100k ish to 47k ish as r14 is adjusted.
__________________
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#924
11-02-2022, 10:03 AM
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R117 27k 3 watt is cold 6volts on one side and like 5mv on the other a 3 watt resistor don’t stay cold and should have a lot more voltage there then what it has now. And the agc pot does vary and the other resistors I had checked more then once.
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#925
11-02-2022, 10:55 AM
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The resistors mentioned determine the over all voltage seen on that pin, another factor is if there is video present or not, so don't expect to see EXACTLY what they say there on the SAMS.
What you got was most likely close enough, and once video is working, it will prob come up into what's on the SAMS.
__________________
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#927
11-02-2022, 12:25 PM
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Well bottom line here is I’m not convinced that there is actually a problem with the IF I believe there is stray voltage from somewhere and it’s corrupting the IF as well as overloading the focus circuit at the same time taxing the power supply. I don’t know where to look at this point. Diodes didn’t help anything. Like I said the video would flicker in and out and the hv would jump 4 kv and back down in an instant. Even though I got video at v2 it was still very distorted whatever this stray voltage is if it is maybe it’s affecting v1 and still carries on to v2 don’t know. When this set powers up there should be enough voltage to run everything even though the thermistor is warming up the voltage is just not there in the beginning and not always does the voltages come up to full after a few minutes it seems intermittent it’s odd never seen anything like this. I wish if there’s something shorting it would burn up that’s a way to find it.
Last edited by timmy; 11-02-2022 at 01:08 PM.
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#928
11-02-2022, 01:24 PM
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I still had the issue with pin 8 v1 resistance check it should be 3.2k but it measured 6.3k this may be the key here since the set still don’t work I can’t say it’s a typo in sams every socket I checked were perfect except for the pin 8 v1. What is the likelihood of one of the old caps to ground that were not changed be shorted or should I say has this been seen before. The last time I checked v1 pin 8 it was 97v should be 100v v2 was 101v.
Last edited by timmy; 11-02-2022 at 01:30 PM.
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#929
11-02-2022, 01:34 PM
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very likely an error, as V2 has an near identical bias on the pin and it's in the 6.3k range, but this has been pointed out before.
__________________
=^-^= Yasashii yoru ni hitori utau uta. Asu wa kimi to utaou. Yume no tsubasa ni notte. いとおしい人のために
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#930
11-02-2022, 01:41 PM
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Quote:
Last edited by timmy; 11-02-2022 at 01:49 PM.
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Linear Mode
