I'm relieved that my signal generator provided some nice traces

You cannot view this attachment.

You cannot view this attachment.

Idk why the trace from that transformer was so sketchy.

Yes sir thank you 

I decided to take a look at this on my scope

Btw here is the source of 12v ac

You cannot view this attachment.

So connecting scope probes directly to cables coming from ac source

You cannot view this attachment.

My phone was struggling to get a full trace left to right despite trying to adjust trigger etc the trace was jittery and flickering real bad

So now connect scope probes to (+) and scope ground to (-)

You cannot view this attachment.

Which I like that but when I had the scope switched to ac I had just a flat line

Then connecting scope probe to (~)

You cannot view this attachment.

So I guess everything is cool. 

I'm off to connect some other stuff to the scope and try to get a better full steady trace.

 

I decided to put a load on it...12k ohm resistor

Similar results

You cannot view this attachment.

More Bruce

 

I have a feeling Bruce says we need some capaci-taters

Thank you sir I wanted to try and replicate this scenario so I did

I had a device with taps on the back for 12v ac so I rigged it up

You cannot view this attachment.




You cannot view this attachment.

Results

You cannot view this attachment.

So...idk

I guess it's time to play some Bruce Hornsby

 

Wow nice amp 

Welcome to the forum

 

Ok guys sorry for the bo bo 

Anyhow removed the old one (no easy task) and got a new one in

You cannot view this attachment.

Seems all is good when measuring the (+) pin and two middle pins (~)

(+) pin reads about 40v DC (have no idea what it is supposed to be


You cannot view this attachment.

But when I read the middle pins I get like 16v ac but what the heck I get 20v DC

You cannot view this attachment.

I think I'll call it a night

 

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

You cannot view this attachment.

You cannot view this attachment.

 

Yes sir appears to go to

-negative terminal of capacitor

You cannot view this attachment.

-and the emitter of the tip31a on the right

You cannot view this attachment.

and a resistor

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

You cannot view this attachment.

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)

You cannot view this attachment.

You cannot view this attachment.

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.

 

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 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. 

You cannot view this attachment.

 

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

 

Quote from: saturated on April 09, 2024, 08:49:16 PMThese two ceramics are still hot enough to cook steaks on....

You cannot view this attachment.

At least small steaks...well done...

So 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.

You cannot view this attachment.

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

Or perhaps I'm unfairly blaming it. 

 


To be continued...the story of the zener diode that was (possibly) framed

Welcome to the forum Valleyslad

 

And I'm ready to put forth another conclusion:

If I measure xxx volts on one end of a resistor.....and ZERO volts on the other end

Guess what


 

It's time to go ISO

 

What it does mean is:

The circuit is open.