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Ozan,

I found a broken trace which I repaired.

I also swapped out a few transistors.

Today I am measuring -0.48 volts when I short across C-E of Q8051.

I understand that 2N2222A is a lower wattage equivalent to the 2N2219. I have ordered additional 2N2219. The 2N2219 was/is shorted.

There is a .3VPP oscillation at the base of Q7042. a 50mv ripple on the +12V and a .2V ripple on the -33.5V.

I am still plugging away at it.

Thank you!

Yes I just downloaded it. Will spend some time reading it.

CH 2 is the same. Vertical Position knobs work in Beam Finder mode.

Thank you Ben for the detailed info - I really appreciate it! Here are my measurements for the reference points you listed:
Junction between C369 and L369: 12.04V
L343 (any side is fine for just sinple voltage measurements): -11.98V
Junction between VR339 and R339: -6.44V
Junction between R311 and R312: 0.897V
Base of Q424: 8.94V
Base of Q324: 9.7V
Base of Q474 and Q347: 11.86V and 10.68V (I assume it's Q374? Can't seem to find Q347)
Emitter of Q414 and Q314: 0.174V and 0.192V

I hope this helps to some extent. Also like I mentioned in another reply, the pot for the A & B VAR knob has been cleaned and it seems to work fine but the UNCAL light stays on no matter how I adjust the knob.

Thanks for the reply. Today I unsoldered about 20 chips that were near the capacitors to see if there were any interruptions in the conductor tracks. I didn't find any interruption.

How do you think I could continue?

- Adjusted Ch1 var and the "uncal" light is off, as I mentioned in post #207706
- The var for A & B time base is in detent, as you can see clearly in my video. That said, I cleaned the pot and it measured smoothly from around 5K ohm to 0 while I turn the red "VAR" knob.
- It is now set to "internal".

Still nothing.

Jeffrey,

The uncal lights and x5 lights are still on. The uncal lights should turn off when you go to the detent position which you will feel. As others have said, the switch could be dirty making the light come on even though it is in teh detent position. Set triggering to a-c or d-c. Set the source switch, lower right corner, to int. Set the v/div switch to .2 or .5V/div and 1ms/div for horiz.. That should get the trace on the screen.

Having two A versions as well as the 453/A and 454, I know there are a number of resistors that are underrated in wattage that caused problems in mine. The 454A has ones that are lower power rated than is being dissipated, especially in the horizontal section. You could very well have resistors that are well out of tolerance or open. Clean the pins and sockets of the transistors. That will cause problems like you are seeing. If you want a list of parts I changed in mine, I will send it.

Mark

Still trying to get a bit further without having to take measurements may yield more info.
If both channels show the same behavior: Since bad contacts are rather frequent with old equipment like this, wiggle the various transistors in the vertical amplifier; they’re all socketed. Also slightly move back and forth vertical position adjustment pot. Don’t know by heart if and where in this model. Preferably do this while power is off.

Should you do measurements at/near the vertical amplifier, be very careful not to short the outputs (or plates) to ground, which very likely would kill the output transistors.

Raymond

On Mon, Dec 23, 2024 at 11:42?AM Jeffrey Wang via groups.io <xwsunrise=
[email protected]> wrote:

How do I troubleshoot the vertical amplifier board?

If this is your first scope repair, you might want to read through this
wonderful document: .
This is from a time when oscilloscope users were more or less expected to
troubleshoot and fix their own equipment :).

Also I doubt it's user error. Cal lights are likely from bad switch contacts as it looks like the knobs are indeed in the dented position.

Sure but since OP did not mention it…

Raymond

That means, no trace without beam finder unless external trigger.…

No it doesn’t because auto-trigger is on…

Did you try channel 2? same result?
Did you play with vertical positions? Both normal pos. and with beam finder (BF) on? Vert. pos. should influence with BF activated as well.
Of course, big offset error in (common) vertical amplifier is quite possible but try and narrow things down first.

Raymond

You can begin troubleshooting the vertical amplifier by chacking voltages at specified test points. They will tell us a lot.
Go to and download the 454A manual, not the operator manual. It will have schematics and board layout diagrams near the end of the manual.

Go to schematic #4 and measure voltages, referenced to chassis ground.

To answer your question from the video, I belive the beam finder works by disconnecting a direct -12V rail from the vertical amplofier, and instead putting it through a 750 ohm resistor. This will reduce the vertical amplifier's deflection range ability, thus you can see the beam when using beam finder. That is the whole point of the beamfinder function anyway, to get the beam in the display.

When the beamfinder is activated, it is in the lower half of the display, indicating the beam is being deflected down out of the display. There is no vertical scretching of the beam, the beam is simply hitting of the phosphors off of the display screen and reflecting light inside the tube.

Again, use a DMM to measure voltages.

Recommend spots:

Junction between C369 and L369

L343 (any side is fine for just sinple voltage measurements)

Junction between VR339 and R339

Junction between R311 and R312

Base of Q424

Base of Q324

Base of Q474 and Q347

Emitter of Q414 and Q314

Thise voltages will help us discover the problem.

Also I doubt it's user error. Cal lights are likely from bad switch contacts as it looks like the knobs are indeed in the dented position.

Benjamin

Center the vertical positioning control with the sensitivity at 1 volt/cm or greater (minimizes signal pickup).

ground vertical input.

at the vertical deflection plates, measure the voltages.? They should be equal.

vary the vertical centering to see if you can get the voltages on each plate to match.? At that point, the trace is centered.? If you can't do this, then the trace won't center.

You can either start from the end or the beginning.

Looking at the schematic, there's one input to the vertical amplifier, which goes through a differential pair.? This produces a positive going and a negative going signal.? Each stage should have the same DC voltage with any signal being of opposite phase. If one signal through the amplifier chain doesn't match, then investigate that stage.? Transistors can be swapped from plus to minus to enable checking bad transistors.

There should be a very good section on how the amplifier works in the manual.? You'll find that the horizontal and vertical amplifiers are quite similar.

One possibility, given that the beam finder switch forces the beam to be on screen by reducing amplifier gain, is that you check around that switch for possible bad contacts.

Harvey

Steps I did on my TDS8000, I hope it might be useful to somebody in the future:

====================
#PPC Board
nvrBase=0xfd0e0000
nvrSize=0x20000
tempBuf=malloc(nvrSize)
memcpy(tempBuf,nvrBase,nvrSize)
fdescriptor=open("dbfs:c:/tds8000_ppc_nvramdump_full.bin",0x0202,0777)
bytesWritten=write(fdescriptor,tempBuf,nvrSize)
close(fdescriptor)

#ACQ Board
nvrSize=0x20000
acqLibReadNVRAM(0,tempBuf,nvrSize)
fdescriptor=open("dbfs:c:/tds8000_acq_nvramdump_full.bin",0x0202,0777)
bytesWritten=write(fdescriptor,tempBuf,nvrSize)
close(fdescriptor)
====================

Happy I was able to store the calibration constants on my device, thanks again

From your settings, it’s my impression that user error still plays a role here:
- Ch1 ampl. still shows “uncal”. Not a cause for no trace but you don’t seem to know it does not match what you say about your settings of the vertical knobs.
- Time base speed setting is still “uncal”. Also, as in remark above.
- Most importantly: The A trigger source is set to *external*. That means, no trace without beam finder unless external trigger.…

Raymond
Reading the basic instructions may help.

I shot another video to demo the current situation:


How do I troubleshoot the vertical amplifier board?

Thank you for the info. I shot another video to demonstrate the issue. I have virtually tested all vertical and horizontal sensitivity combinations to no avail. I just realized that the UNCAL light was on for Channel 1 but I also adjust the var knob after I shot the video so the light is off. That said, it didn't change anything. I hope this video helps in identifying the issues.


Thanks!

Hello Gianni,

maybe Dorit and I can get you the paper, if it is helpful. But it will
take some time.


If yes, please let me know via a private email.


Tam

--
With best regards
Tam HANNA

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Hi Anita,

While you are at it, if you haven't already done them, you might want to take a look at the Tek list of "factory updates/mods" for the 575. There are a BUNCH of them. I'm wading my way through them now on my 575. I'm about half-way there.

Here's the link to the 575 TekWiki, where quite a few of the critical mods are listed individually, there in the "Manuals" Section. FWIW, there is also a complete assembled "all mods" document floating around somewhere, but I didn't see it here. I might have missed it. It has every mod documentation assembled into one PDF

Anyway, the link;

Several of these mods did make a measurable improvement in my unit's performance. Some were reliability improvements.

Hope this helps.

Keith

?ann mán., 23. des. 2024 kl. 03:39 skrifa?i Jeffrey Wang via groups.io
<xwsunrise@...>:

I’m curious, why in beam finder mode, the waveform and the trace were
clearly visible - it’s just that the screen was vertically compresses,
which I suppose it normal. That said, everything disappeared as soon as I
let go off the momentary switch. I did some research and it seems that the
beam finder mode bypasses the intensity control circuitry so does it mean
this circuitry is faulty? How can I verify that and troubleshoot?

For most of the video your vertical sensitivity was set to 20mV/DIV, which
is way too sensitive. You also have the variable control out of the detent
as witnessed by the uncal light. This would lead to a trace that is mostly
off screen.
This is not to say that there isn’t a problem with the problem with the
scope, but at those settings the video doesn’t show a problem, it might
well be WAI.

Try setting the scope to 0.2V/DIV (VAR in detent) and e.g. 1ms/DIV and see
whether you can then get a trace on the CRT.