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After some time away from this fix, I'm now trying to work at it again.
However, I'm becoming frustrated at my current lack of understanding. I'm reading as much as I can about electronics, but my current level of knowledge, for circuit troubleshooting, is pretty weak.

I've resorted to just walking through a schematic and testing each part as I go. I started with the power supply and tested a fair number of parts without too many replacements. I've replaced some of the main caps as well as a few transistors on a couple of the boards.
I've tried to limit any de-soldering to only items I truly think might have issues. Still nothing so far.

Last night I did find another transistor with issue (reading roughly 2.2 volts across c,e while normal b,c and b,e were fine at roughly 6.8-7.4 range, iirc). However, swapping this with a good one (from another area on the board, supposedly not part of the same circuit) did nothing for me.

Here's what I noticed: I can't seem to get any trace on screen unless I press the beam finder. On top of that, I can't seem to get anything for a trace other than a line when pressing beam finder. I assume this isn't normal, but this scope was supposed to be my training device, so I could easily be wrong.
Things like triggering do seem to work. I slow things down and watch the beam trace across the display, i can affect it with triggering, etc. So it also appears as though it's stuck in "GND" mode and regardless of AC/DC setting, and any input (tried low voltage DC and AC), I only get that line (again, with the beam finder).

I can adjust the line up and down. I've adjusted a few items, based on the service manual, to get voltages in check. The main power supply voltages are within spec. 110 is the closest to being out of tolerance at roughly 112.6 Vdc, but in general, they are either dead on or well within spec.

So my main question is this: since most of the troubleshooting items, which I've read about, involve reviewing a trace, is that my primary section to review now? I assume that even using the beam finder, I should see something more than a line. yet no input provides any changes.

I try to follow the troubleshooting steps in the manual, but they get vague at some point because they assume I have a specific level of knowledge already (which I apparently do not).

If I'm missing something super obvious, I would appreciate a good kick in the right direction.
Otherwise, I'll just replace that one transistor and keep moving along with my testing to see what I can figure out (mostly by luck).

I appreciate the help so far. It's definitely helped to get me this far. I also really wish I had another scope to test ripple/etc, but I do not. I have a true rms multimeter and an esr meter, if that helps anyone.

-Josh


--- In TekScopes@..., "i814u2.geo" <fakecrap@...> wrote:

I checked the triggering section some more and it seems to work as I would expect. Setting it to normal and adjusting the trigger point does change what I see on the screen (I just have to hold the beam finder button down the whole time). Single trigger works, etc.


I couldn't get the same "open" reading on the vertical plates in any subsequent tests. However I'm not doing anything differently either. I don't know what I did wrong there. I'll leave it on longer and test again to see what happens.

-Josh

--- In TekScopes@..., "i814u2.geo" wrote:

Triggering first: If I mess with triggering controls, it does appear as though it is triggering properly. I'll need to check more tomorrow.

Voltages for the deflection plates are as follows:
Horizontal R (manual states 52.1): 48.5
Horizontal L (manual states 48.1): 50.6
I triple checked those readings. They are fairly steady and I was testing the proper points (based on matching parts and schematics).

The vertical off pin 9 (is this the bottom plate?) has a spec of 36.6. I read roughly 38 but that value fluctuates a bit while slowly decreasing. Pin 12 has a spec of 32.5 but starts around 30 and fluctuates while slowly decreasing.

Another item I notice: when first turned on, the scope shows channel 1 toward the top of the screen when pushing in beam finder button. I can't adjust over the normal range. Once it warms up more, I can at least center the beam (though it's a bit jumpy). Channel 2 doesn't have this issue. I assume this is a separate issue (since it only happens on one channel) but I mention it in case it's helpful.

After a while the vertical deflection plate voltages can't be read and my meter shows the circuit is open. This sounds like a cold solder joint type issue (or a part doing the same) but where would I start with that? Just trace voltages back from the deflection plates until things are stable again? Or am I totally off on that idea?

Also, I'm assuming the fact that the horizontal voltages appear swapped is simply a coincidence due to the spec values being so close to start.

Again, thanks for the help. I'm eager to finish this project up and get a working scope.

Josh

--- In TekScopes@..., "Tom Miller" wrote:

The 112 is ok for the 110 measurement.

Resistance measurements depend on several variables including lead polarity, meter type, and active device junction variables.

You need to make a dc voltage measurement on each of the deflection plates (left and right, top and bottom) and report the measurements. Let's see if the beam is anywhere near the center.

Next thing to check is the triggering. Are you getting a sweep?

That should keep you busy for a while :).

Tom




----- Original Message -----
From: i814u2.geo
To: TekScopes@...
Sent: Sunday, January 20, 2013 3:45 PM
Subject: [TekScopes] 475 progress but another road-block



So, with the help of the folks here and some troubleshooting, I've gotten my 475 closer to being usable again.

However, I'm stuck at a new spot now. I am getting almost perfect voltages at each test point except for the 110V TP which shows roughly 112.4 (which is still within tolerance, just not ideal).
The odd thing is that when I test resistance to ground, only about half of the points are within tolerance. 110, -15, U50, and 105 all show much more resistance than they should. Especially -15 which is showing several K of resistance (book shows it should be 480 ohms).

At some point, I also found a trace that was broken and made the repair. I now get a display if I use the beam finder button. However, I do not get a display without using that button. When I adjust knobs on the front, that "beam found trace" does move (mostly as I would expect). It doesn't seem to stay perfectly still in all cases, but I'm assuming that is because something is still bad and causing issues (including the resistance variances).

I do not have another scope in order to test ripple. I've been trying to follow the troubleshooting flow chart in the manual, but I may be getting confused. If I press the beam finder and adjust the trace to the center, but then release the beam finder button and still see no trace, should I be disconnecting the delay line as my next test?
Or have I gotten ahead of myself?

-Josh

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