Author Topic: Can someone explain for me?  (Read 6184 times)

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Offline lilshawn

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Re: Can someone explain for me?
« Reply #25 on: January 30, 2017, 03:54:36 pm »
I probed a bunch of places and got this:

I double checked all the resistor values and they are within a few percent of nominal.

the transformer (t901) provides voltage through D905 provides voltage (about 20-30 volts) for the vertical deflection circuit. it's shown in the schematic snippet, but I don't think it has a bearing on what's happening on the B+ circuit side. I have lifted this diode out of the circuit for testing.

I also do not read any voltage output from this diode. I'm thinking i'm not getting a pulsation in the B+ output (instead just straight DC) which is not allowing the transformer to do tranformer things and produce electricity. (the transformer needing a changing electric current to produce the magnetic field to produce on the secondary)
« Last Edit: January 30, 2017, 04:06:20 pm by lilshawn »
 

Offline Andy Watson

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Re: Can someone explain for me?
« Reply #26 on: January 30, 2017, 04:04:30 pm »
Q902 is dead. There should not be 12V difference between its emiiter and base.
 

Offline lilshawn

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Re: Can someone explain for me?
« Reply #27 on: January 30, 2017, 04:11:09 pm »
I figured as much. I noticed that the voltage was much too high there. also... no oscillation or pulsation in the B+ to drive the secondary circuit through T901. no voltage output.

of course q902 was the only part I was unable to immediately source new...I had to take one from another chassis. i'm betting that one is dead to then (it does check fine with the low voltage a B&K 510 transistor checker supplies so I thought it could have been okay)

thanks for the insight, I'll get some replacements and have another go at it.
 

Offline T3sl4co1l

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Re: Can someone explain for me?
« Reply #28 on: January 30, 2017, 04:30:48 pm »
If Q902 is open, Q901 shouldn't be on.

Think you're going to have to find a new one of that, too...

Tim
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Offline lilshawn

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Re: Can someone explain for me?
« Reply #29 on: January 30, 2017, 04:47:04 pm »
Q901 I have. I have also replaced it again. (unless it has gone wrong again now in my all my testing.)

I just got a new Q902 and replaced it. the output at f902 is now matching bridge output. I also noticed a faint tick in the circuit when powered up so now I think something else has gone.  |O

 

Offline Armadillo

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Re: Can someone explain for me?
« Reply #30 on: January 30, 2017, 04:50:22 pm »
Q902 is dead. There should not be 12V difference between its emiiter and base.

+1

Q02 is shorted and Q903 is off, which means at least 36mA goes into the base of Q901 turning it full on. Though Q901 is able to withstand max base current 5A, other parameters may have been exceeded, so Replace Q902 and still need to check Q901.
« Last Edit: January 30, 2017, 05:01:00 pm by Armadillo »
 

Offline Armadillo

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Re: Can someone explain for me?
« Reply #31 on: January 30, 2017, 04:54:09 pm »
Q901 I have. I have also replaced it again. (unless it has gone wrong again now in my all my testing.)

I just got a new Q902 and replaced it. the output at f902 is now matching bridge output. I also noticed a faint tick in the circuit when powered up so now I think something else has gone.  |O

You are getting near, probe the voltages again.
 

Offline Armadillo

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Offline lilshawn

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Re: Can someone explain for me?
« Reply #33 on: January 30, 2017, 05:09:37 pm »
I've replaced Q901, tested bad. the replacement of Q902 could have pushed it over the edge and killed it.

Also dropped my lightbulb load down to 40 watts.

B+output is ~96 volts now. which from what I read elsewhere is about right for weird lightbulb load apparently.

also getting oscillation in the circuit so now i'm getting volt output at D905 from the transformer.



hopefully now I can hook up the rest of the circuits and it NOT blow up (fingers crossed.)

Just 4 transistors, I think is high time you get one of this;

http://www.ebay.com/itm/LCR-T4-ESR-Meter-Transistor-Tester-Diode-Triode-Capacitance-SCR-Inductance-M328-/161932407715?hash=item25b3ec73a3:g:k3wAAOSwCQNWgllX


I sort of looked something similar about a year ago when I was in the market for an LCR meter (specifically for inductance)... but since I already transistor checker, and voltmeter that does capacitacneI figured I wouldn't bother.
 


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