Yes sir thanks I was able to find some old pics of the original part

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The rectifier is installed backwards.

Yes sir appears to go to

-negative terminal of capacitor

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-and the emitter of the tip31a on the right

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and a resistor

Follow the trace from the bridge + lead to filter cap.  Is it going to + or - end of cap?

Quote from: markorock37 on April 13, 2024, 02:57:58 PMI don't see 2SA872 on Mouser, is KSA992 a good sub?

Yes, those should work.

Meanwhile... experienced my first Chernobyl.

So this metronome I had removed the bridge rectifier a while back and it tested good...oh well

Put a new one in today.... thought it would be fun to hook my meter to the leads before I clipped em and read ac and DC on the different leads.

So I solder it in...crudely soldered the transformer wires back making sure I put the right ones in order.  Plug it in...I'm gathering up my meter and test leads and I hear woosh and see lots of smoke

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And liquid 

Later I was outside and thinking did I put it in backwards or something...or leave a solder bridge?  But looks like the orientation is correct and the solder reasonable (these pics are post meltdown)

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Im beyond hoping this thing will be fixed but I did want to replace that part.

Meanwhile I put it on my ugly dbt after the fact yes it was glowing.

 

I don't see 2SA872 on Mouser, is KSA992 a good sub?

Thanks G1 it's a gorgeous day today with plenty of sunshine so I'm actually fixing to take some good pics of this scope so I can put it on the auction site.  Hope is waning that the ever so coveted green trace will ever appear.
I'm happy that it's been a great learning tool but at this point I don't even know if the CRT is any good. When I first got it there was a slight glow at the small end and it gets dimmer and dimmer.
Also there are a bunch of rusty trim pots then another board has an open somewhere (at the minimum).
A 68v zener is cheap though I might need to see that localized issue settled.
Also I really like that arrow pointing at that node and a diagram of a square wave.
Would be cool to see if that is there with my other scope.
 

Quote from: saturated on April 12, 2024, 07:53:18 PMSo I'm going out on a limb here and proposing that the 8k ohm 10w resistor is shorted to ground.  It measures 170v on one end and zero on the other.
A quick look at the schematic (a forensically enhanced version kindly provided by the Mighty Mick) to me places cross hairs directly on the zener diode.

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So I'm guessing that the zener diode is shorted...idk.

That's not going out on a limb, that is good solid logic. (assuming you verified the resistor is ok) 

Quote from: saturated on April 11, 2024, 10:29:56 PMWhat it does mean is:

The circuit is open.

 

I decided to have a look at this scenario...of course I had seen it and read it in books and kind of unwillingly accepted it.

My point being...take an open circuit...add some resistors in series to the positive side...and your gonna measure the same voltage anywhere along that open series...doesn't matter....one resistor...two resistors...three resistors....there is no voltage drop. 

I had to try it.  I made up a three resistor open series circuit connected to 5v.

Well you guys know what happens and already know this.  But seeing it in practice really firmly eliminated any skepticism. 

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Obviously this is way over simplified but it still is a powerful tool when probing.