bent neck CRT pins...

[Sparkey55]

Re: bent neck CRT pins...

The PSU is not oscillating at least with the 12W bulb as the DC "dim bulb tester." I used another scope to determine this However I wonder if I should up the wattage of that bulb...

It uses a single TO220 PNP transistor as the oscillator, and uses same circuit topology as a Joule Thief, except power is taken from the secondary. This transistor is just to the lower/right of the 'flyback,' plastic body facing left. Negative feedback is done by changing the voltage on the feedback winding (on a Joule Thief, the feedback winding is connected to V+; on this circuit, an op amp output through a resistor.)

The transistor does not appear shorted but apparently having trouble oscillating. I should check the feedback voltage, and assuming it works like a Joule Thief, ... hmm...

Increasing the watt rating of the light bulb has the effect of lowering the bulb resistance which inturn decreases the voltage drop across the bulb and allows more voltage to be seen across the scope primary windings. Lowering the watt rating of the bulb will increase the voltage across the bulb thus decreasing the voltage to the scope.

[Sparkey55]

Re: bent neck CRT pins...

Ahh... I found schematics and placement information that's closer than found in the service guide; it looks like a later version of the board was in the device. Still no idea why it seems shorted when plugged in (light bulb in place of the fuse burns brightly) but without the PSU the light is out.

When disconnecting the anode and cathode/filament (by the base socket), the light bulb still burns brightly.

One oddity was that I hooked up my sencore to the "flyback" output (before the multiplier). At first I was getting a Q factor of around 9... Then after a bit of futzing with it, the meter got a Q factor of 29. I hope I don't have a fried flyback that has an intermittent short. I was testing in-circuit...

Woah
http://www.ebay.com/itm/TEKTRONIX-GB...-/272182368706 - What was Tektronix thinking? Look at the bodge job at the lower left of the board...

Sigh... hope that I can fix mine somehow...

Your HV supply is bad. The incased HV tripler/doubler are notorious for burning out the diodes or the caps in them. A shorted or over current heater winding could cause the flyback coils to have shorted turns or open windings. Flash overs in the crt are a known killer of these.

[stj]

Re: bent neck CRT pins...

if it is the trippler and not the initial transformer, i would try to decap it.
or if internal schems exist - clone it.

[Sparkey55]

Re: bent neck CRT pins...

if it is the trippler and not the initial transformer, i would try to decap it.
or if internal schems exist - clone it.

If it is epoxy encapsulated easier said than done.

[eccerr0r]

Re: bent neck CRT pins...

Yes this is epoxy potted. Bleah. But still wondering if a cracked tube could have caused the untimely death of the multiplier or the "flyback" ...

However as far as I know, the heater was fine, there were no shorts in the system other than possible (and it's still not confirmed) leaking of the vacuum. And yeah the schems of the internal guts appear to be documented. It appears to be a 6-stage hexupler(?).

I wonder if it's safe to run a resistor between the multiplier and "flyback" to see if I can isolate the fault. Neither appear to be shorted as far as I can tell, but I don't know how many ohms is equivalent to a "short"...

So are multipliers/flybacks generically easy to fry or this specific model?

[Sparkey55]

Re: bent neck CRT pins...

Yes this is epoxy potted. Bleah. But still wondering if a cracked tube could have caused the untimely death of the multiplier or the "flyback" ...

However as far as I know, the heater was fine, there were no shorts in the system other than possible (and it's still not confirmed) leaking of the vacuum. And yeah the schems of the internal guts appear to be documented. It appears to be a 6-stage hexupler(?).

I wonder if it's safe to run a resistor between the multiplier and "flyback" to see if I can isolate the fault. Neither appear to be shorted as far as I can tell, but I don't know how many ohms is equivalent to a "short"...

So are multipliers/flybacks generically easy to fry or this specific model?

YES.
The heater is spaced very close to the cathode. Heater to cathode shorts can happen anytime but usually during rough handling while turned, bumped hard or dropped. Letting in air is almost a guarranteed way of causing a short if just for a moment at least.
A ring tester is used to test flybacks for shorts.

[stj]

Re: bent neck CRT pins...

if you fit a resistor (like in the ebay foto!!) make sure it is rated for the correct voltage.

as for epoxy - big fucking deal - i have taken epoxy potted stuff appart as part of my reverse engineering for the MAME project loads of times.

heat or paint stripper like Nitromors will usually break it up or soften it.

can you link / post the schems.

[R_J]

Re: bent neck CRT pins...

Is this the service manual you have? https://cdn.badcaps-static.com/pdfs/...04f7d00b0b.pdf

[Sparkey55]

Re: bent neck CRT pins...

Is this the service manual you have? https://cdn.badcaps-static.com/pdfs/...04f7d00b0b.pdf

If that is the scope that he has then he does not need to dick around with it. A 400Mhz scope is not a cheap toy to fuck with. Buy a 40 or 60Mhz scope to learn on first. Cheap ones on ebay can be had for $80 or less.

[eccerr0r]

Re: bent neck CRT pins...

No, the schematic of this board that I own now is actually from the 2445a. The 2465b should be similar but the 2467b is a completely different beast and incompatible at least for drop in replacement. Mine's the older non-suffixed version...very old.

The schematic on pg 436 of that posted link looks very similar. Layout on pg 434 looks close too.

If there was any jarring or (sudden) leaking of the CRT it all happened when the PSU was off. And currently it's off and I see no shorts, so this is really weird.

[Sparkey55]

Re: bent neck CRT pins...

Shorts between elements in a vacuume tube can be intermintent and created when heated to operating temps or above. Voltage flashovers can occur quickly and do damage to the tube. Heater to cathode shorts can be intermittent also although mostly while heated to temp. Any tube that has been breached of its vacuume will become gassy and die a slow death if not instantly go to smoke.

[R_J]

Re: bent neck CRT pins...

I just went by the model that was in post #19 and the hv board he posted looked very similar
Oh well, never mind.

[stj]

Re: bent neck CRT pins...

so this?

it looks not just easy to clone,
but i suspect you could test much of it from the outside with a component tester!

[eccerr0r]

Re: bent neck CRT pins...

Yeah, that's the multiplier. Next I want to desolder the flyback from the multiplier so I can separate the resistance. Indeed it's a fairly simple blackbox.

So far other than the resistance of the flyback secondary, I did see that 10K ohms between 2 and 14 though the other pins are somewhat clouded by the outside circuitry. So far that was the only set of pins other than the filament feedthroughs that have less than ~ 8Mohms that I've probed so far...

[stj]

Re: bent neck CRT pins...

i would be probing that brick in relation to the diodes as much as anything else.

[redwire]

Re: bent neck CRT pins...

As far as air in the CRT goes, it should have a getter spot turned white.

I've had CRT's with no or low high voltage but the HOT working hard and running hot. Disconnecting the 2nd anode I could draw a big arc, the high voltage would come right up.
Found the problem was a leaky/shorted HV rectifier. AC going to the CRT loads down the HV, it's the CRT 2nd anode capacitance.
I don't suggest OP try the arc test if he doesn't have experience, but it's an old trick we used in the shop to troubleshoot HV problems.

[eccerr0r]

Re: bent neck CRT pins...

Yeah, I'm still hunting for the getter spot. Looking at tubes on eBay I couldn't find the getter spot... Still too lazy to remove the shields.

I desoldered the high voltage inputs to the multiplier... The inputs into the multiplier appear to be OPEN, or at least over range on my ohmmeter (when not connected to any load). However I don't have a high voltage ohmmeter so my DMM can't forward bias the diodes...

The secondary of the flyback I'm seeing resistances:

COM - 0V (still connected to circuit) -
tap1 4.27 ohms -300V (to inversion, still connected to circuit) Q=12
tap2 30.69 ohms -1900V (to multiplier for inversion, desoldered) Q=42
far pin 85.08 ohms +HV (to multiplier, desoldered) Q=46

My sencore Q meter seems very flaky. ^H^H^H^H^H^H^H sensitive... Weird. I had my hand on all the pins of the HOT and apparently leakage through my hand causes the Q factor drops immensely.

That -300V output - for focus
The -1900V output - connected to Cathode, also generates -900V slot lens

That -300V output seems very low Q, but there's stuff on the board that could be damping.

Interesting however ("calibration"): I have this filter/ballast choke from a dead CFL. As is I get a Q of 60 out of circuit. However if I hold my fingers against the two pins, I can get the Q to drop to 30...

[R_J]

Re: bent neck CRT pins...

The getter spot is not going to tell you anything about the condition of the tube, you can smash the tube and the spot and the getter itself won't change, https://en.wikipedia.org/wiki/Getter
The getter is usually in the neck of crt's http://www.crtsite.com/oscilloscope%20crt.html

Checking dc resistance of the transformer will only tell you if a winding is open, you could ring test it,
it only takes on winding to be shorted to the one beside it to short the transformer (stop it from working) but the resistance change will be next to nothing.

[eccerr0r]

Re: bent neck CRT pins...

Yeah, those Q numbers is the ring test on my Sencore. Despite the -300V tap has a low Q, but if there is a short there, it should also make the Q of the other ports on the secondary go down... Weird.

Ok this is the picture I wanted: http://www.crtsite.com/big/crt/TEK%203-big.jpg Now I'm curious how long it takes to completely eat away all the getter deposit. I just wonder if I killed the tube seal by bending the pin back. I think I sort of know why the pin was bent to begin with: the shield is just barely big enough for the neck and the pins will hit against the shield if you blindly push it in (the aperture in the shield gives enough space to bend back). I think actually the correct solution was to trim the pins and not bend them to fit the tube into the shield.

As I still don't feel like removing the tube, staring from the end I can barely make out the two getter spots. They are still dark colorred... a good sign... alas due to the extreme angle I can't tell if it's still shiny as the glass refractive index would look shiny and reflective.

[eccerr0r]

Re: bent neck CRT pins...

I disconnected the two caps that's connected to the -300V tap (C1950 and C1889) and remeasured the Q with the sencore (note, primary is still connected in circuit):

pin2 Common -
pin7 -300V (Focus) Q=34
pin10 -1900V to multiplier (Cathode) Q=47
pin 8 +Vhigh to multiplier (Anode) Q=56

This looks good! Or is it?
The funny thing is if I touch any pin while running the Q test, the Q bombs to almost 0. Removing my finger from the pin, it goes back to normal... Seems this flyback loses the field pretty quickly.

Now if I short the filament winding... Q drops to 5. Shows the Sencore is working.

As far as I understand this, this is indicative of a good flyback (unless it has high voltage leaking).

This is weird. Perhaps that 12W bulb is not quite enough to reach the starting current? Hmm...