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Hi David,

here is the link to the original document made by Hakan (aka Zenith):



Hope this helps,

Leo

I had my first experience with letting the magic smoke out of something
tonight.

The new filter caps finally arrived from Mouser and I replaced C806. I then
put the power supply partly back into the instrument. I didn't bother to
connect the main interface board or the back panel inputs and outputs as I was
only interested in whether the power rails were good. I should have connected
even less and just examined the rails coming off the unregulated supply, but I
did connect up the power cables going to the LV regulator and the horizontal
board.

Most of the power rails were still off as I saw them last time: everyone other
than the +130 and +40 rails were high, +130 is basically spot on, and +40 is
still very low.

While I was probing the power supply however, I heard a clicking sound and
smelled smoke. One of the resistors on the horizontal board had burned up.
Checking the manual it's R578, which is a 1/2 W, 2.5 K ohms film resistor,
which I have replacements for in stock. I checked Q578 in the component
checker and it looks like it survived the experience, as did several other
transistors in the same area, so maybe I didn't kill things too badly.

Regardless, the failure to fix the low +40 V rail combined with burning up a
component on another board has taken the wind out of my sails for the evening.
Maybe I'm learning things, but this is NOT proving to be as enjoyable an
experience as working on the 475 and 475A had been.

One lesson I'm taking away from this is that I should not reconnect the power
supply to the rest of the machine until I am sure that I've fixed the parts
I'm trying to fix.

-- Jeff Dutky

Hi,

I have successfully retrofitted the 5S14N sampling plugin with readout
for use with the 54xx scopes, by basically recreating the 7S14 readout
board and wiring it in, thus creating a 5S14.

See the photos: /g/TekScopes/album?id=261631

If there is any interest, I'm willing to do a little description of
the project, and share the design files.
I have a couple of PCBs which I can give out for the price of the postage.
Mostly probably useful in the EU, elsewhere it will likely be cheaper
just to get them from China.

Let me know if anyone is interested, then I'll take the time in the
coming days to do a writeup on it, as while it is not a complex
project, there were some obstacles, which may be interesting to share.

Szabolcs

I looked for that document in the files section but failed to find it :-(

I even tried search terms like 22xx and supplies.

I found a doc on line but that talks about Q9070, a FET which isnt on my
schematic.

Dave


On 16/03/2021 21:26, satbeginner wrote:

Hi Ozan,

Try to find in the Files section a document called (I believe) "Repair tips for 22XX power supplies"

I'm not at home now, so I can not look for a direct link right now, but the document made by Hakan, also a member here, described how to eliminate and look for which part of the ps is failing.

Usually it is the first switcher, but the document describes how to test for that.

Let me know if you found the doc.

Leo

Hi Ozan,

Try to find in the Files section a document called (I believe) "Repair tips for 22XX power supplies"

I'm not at home now, so I can not look for a direct link right now, but the document made by Hakan, also a member here, described how to eliminate and look for which part of the ps is failing.

Usually it is the first switcher, but the document describes how to test for that.

Let me know if you found the doc.

Leo

I checked the DC recovery diodes in the HV supply as listed in other

thread

(all under the plastic cover and they are ok.
Any other suggestions?

Note that checking the leakage of those diodes is important, just a DVM
diode check doesn't discover problems.

It looks like the behavior of your 485 is different in different settings.
As the first issue are you debugging the intensity? Do you have too bright,
or too dim brightness, does intensity control make any difference?

HV supply voltage of 2000V is low. What is the impedance of your 1000x
probe? Looking at the schematic “CATH REG” can only adjust ~ +/-100V so
this is outside adjustment range. Should be the first thing to fix since
everything else with intensity depends on it.

Feedback loop around U1624 uses +50V at the top of R1642B as the
reference. Is +50V correct?
If you look at pins 2 and 3 of U1624 what voltage do you measure (should
be essentially the same and close to 0V).

Once you fix the HV supply if intensity is still problematic:
There are multiple posts about DC restorer issues I recommend you search
"DC restorer" "Grid Bias" for useful information.

The ones I know well are: Topic #180156: Although different equipment,
this topic has some DC restorer debug. Topic #180235 is a 485 with
intensity control issues. In particular looking at the circuitry around
intensity control pots. If you review both chains from start there is some
relevant information.

For time base issues, in the problematic 3 fastest settings how does the
"A Sweep" and "A gate" signals look? They are easily available at the back
of the scope with a BNC connection.
Ozan

A couple of questions and comments.

I see you have indicated that there is a foam product present in the
container. Can you better describe the appearance of it to help define
what it is? Yes, there are foam products releasing agents that can cause
deleterious effects on metals and such.


Greg