----- 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

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

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

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

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

------------------------------------

Yahoo! Groups Links

Josh,

I am jumping onto this thread late & I haven't been following it closely, so you may have already tried what I am about to suggest.

I assume all the power supplies are close to what they should be, or the beamfinder probably wouldn't work.


It sounds like one side of your vert amp is bad, which is driving the trace off screen.
The beam finder restricts the output amp swing so that a trace will occur on-screen if the CRT & high voltage are OK.
Do you get the same result on both channels? Try them one at a time.

If so, then the problem is probably after the vert mode switch (Ch1, Ch2, Add, Alt, etc)
If you select ch2 & then invert it, does the beam finder look the same ?

You can isolate the problem area with a short jumper wire.
The amplifier after the mode switch is usually push-pull, so any unbalance will drive the trace off screen.
You will notice that the top half of the board is a folded image of the bottom half.

You can safely short opposite sides of the amplifier together, NOT to ground or anything else!!
If you short both sides of the delay line together, does the trace return ?
If so, the problem is prior to that point, & probably after the Mode switch.

Working backwards from the delay line, short like points of the prior stage.
Keep working back towards the input until you find the stage where the short has no effect.
That is where you will find your problem.

Usually ( but not always), the case of the transistors is tied to the collector.
So shorting opposing transistor cases together is the easiest way to isolate the problem.


?
HankC, Boston
WA1HOS

Hi Josh,
I'm a little late in looking at this also….so…
turn your intensity down first…. then


power off.

disconnect the vert plates at the crt or vert amp. but be careful the crt pins are very delicate.
this will center the vert beam….

then also disconnect the horz plates….. this will center the horz…..

power on...
adjust your intensity for a easily seen dot about in the center of the crt……not to bright or you could burn the crt…..

if the dot can be seen at the center and can go from dim to bright your HV and crt are ok.
now power off and reconnect just the vert plates.

power back up and select to see only channel 1
put the input selector to GND. on both channels.

now you should be able to move channel 1 vert position up and down and see the trace move from top to bottom.

choose channel 2 for display
gnd the input and move channel 2 vert position up and down and see the trace move from top to bottom.
center the dot and then measure both vert plates…they should be about the same.


power off and disconnect the vert plates.



now do the horizontal….
but first make sure BOTH verts inputs are in GND

reconnect the horz plates….
put time/div to X,Y mode

power up and move the horz position full left then full right
the dot should move full left then full right

center the dot and then measure both horz plates…they should be about the same.

put time/div in 1ms….do you get a line from left to right?

tell me the results of all test .


jim




On Jun 5, 2013, at 7:25 PM, i814u2.geo <fakecrap@...> wrote:

Alright, I've been going over this for two nights now and I'm only barely making progress.
Sadly, that's probably because of dumb luck and not any skill/understanding yet.

I tested more transistors or at least made sure things weren't loose. I also swapped one from the B trigger for the one that I found was going bad.
I don't really think that fully helped, but I am starting to at least get the start of a test trace.
It still only shows while pressing the beam finder.

So it does seem like things are working except for the vert amp. Here is where I'm stuck.

This is what I know: schematic shows that pin 9 from U470 (vert amp) should have about 36.6V+ I see 34.3. Pin 12 shows it should have 32.5V+ and I see 32.7.

Not sure how much that matters yet, I just mention it because I measured it and it seemed odd.

Next: I have re-read the suggestions below, from HankC, and I'm honestly lost. I can't see where the board appears to be a folded image of itself. I've stared at the preamp section as well as the amp (which is after the delay line, after the switch, if I understand the diagram correctly).

Here are the answers to HankC's questions, maybe that will help more:
Right now, the power supply readings are within spec. I'm particular and so I'd like them to be closer but they are currently within tolerances. Resistance to ground doesn't match in each case, but right now nothing is completely shorted or completely open.

If I short the delay line, I don't see the trace. If I do it while pressing the beam finder button, it effectively starts to bring the square wave back to a line. Correct me if I'm doing something wrong here.

Things are the same regardless of channel. Pressing invert on CH2 does seem to affect the trace shown with the beam finder. Also, things like triggering work how I would expect, and I can move the trace around (including the angle). I just can't get it to work without the beam finder at this point.

Just so I'm clear, for the shorting process, are you talking about the delay line on the amp board or the preamp board?
Staring at the vert amp board, or the preamp board, I just can't clearly see which section is supposed to be the set of matching sides. I may be looking too literally though.

I just tested U450 for expected voltages and nothing was grossly off. Things were maybe 200 mV off in some cases, but nothing like entire volts off or negative instead of positive. I realize that the mV may still make a difference, but I'm just pointing out that the output sides made sense based on the inputs.

I look forward to some clarification of what board I should test at this point (based on my answers). Also, if I'm doing something wrong, please let me know. I'm anxious to conquer this task and move forward with the next one (as well as furthering my education with this stuff).

Also, if I center the horizontal control, I get voltage readings (at the lines going to the plates) that are not at all as expected (based on the schematic's blue lettering). The left plate is roughly 64.4V (schematic shows 48.1) and the right plate is 34.4V (schematic shows 52.1). I assume that's just an additional issue, not related; again, I'm just adding things I actually know. Odds are high that this will be just another item to review once I can get things up and running and calibrate the machine.

Thanks, as always.

-Josh

--- In TekScopes@..., HankC <hankc918@> wrote:

Josh,

I am jumping onto this thread late & I haven't been following it closely, so you may have already tried what I am about to suggest.

I assume all the power supplies are close to what they should be, or the beamfinder probably wouldn't work.


It sounds like one side of your vert amp is bad, which is driving the trace off screen.
The beam finder restricts the output amp swing so that a trace will occur on-screen if the CRT & high voltage are OK.
Do you get the same result on both channels? Try them one at a time.

If so, then the problem is probably after the vert mode switch (Ch1, Ch2, Add, Alt, etc)
If you select ch2 & then invert it, does the beam finder look the same ?

You can isolate the problem area with a short jumper wire.
The amplifier after the mode switch is usually push-pull, so any unbalance will drive the trace off screen.
You will notice that the top half of the board is a folded image of the bottom half.

You can safely short opposite sides of the amplifier together, NOT to ground or anything else!!
If you short both sides of the delay line together, does the trace return ?
If so, the problem is prior to that point, & probably after the Mode switch.

Working backwards from the delay line, short like points of the prior stage.
Keep working back towards the input until you find the stage where the short has no effect.
That is where you will find your problem.

Usually ( but not always), the case of the transistors is tied to the collector.
So shorting opposing transistor cases together is the easiest way to isolate the problem.



HankC, Boston
WA1HOS

ok, the roughly centered dot with NO connections to the deflection plates means the problems are probably with the horz and vertical amps.
find the vertical connections and reconnect the vertical to the crt and run the position test I described.

what happens???
jim


On Jun 6, 2013, at 4:39 PM, "i814u2.geo" <fakecrap@...> wrote:

Disconnected pins for vertical (all 4, to be certain) and desoldered wires for horizontal.
No dot appears, unless I press the beam finder button. Then I get a fuzzy dot roughly in the middle of the X axis (slightly to the left), and roughly half way up the Y axis (assume 0,0 is the center).
Hopefully this doesn't point to a crappy CRT and it tells you something brilliant about a board that I should inspect next.

Again, I'm now anxious for a response to see how much time I've wasted on this thing.
You mention HV as well as CRT, is there any to check which is a common failure? Or do I just go and test whatever the manual provides values for in that area?

Also, I haven't tested voltages that high before, so I'll be researching that first. Any must-read articles/books would be appreciated. Otherwise I'll research what I can do with the gear I have (if anything) and some creative test circuitry. I realize there are some theoretical setups I could build to test a relative value, etc, but I want to know I'm testing safely, not just theoretically.

thanks again

Josh

--- In TekScopes@..., Jim Popwell Jr <jpopwell@> wrote:

Hi Josh,
I'm a little late in looking at this also….so…
turn your intensity down first…. then


power off.

disconnect the vert plates at the crt or vert amp. but be careful the crt pins are very delicate.
this will center the vert beam….

then also disconnect the horz plates….. this will center the horz…..

power on...
adjust your intensity for a easily seen dot about in the center of the crt……not to bright or you could burn the crt…..

if the dot can be seen at the center and can go from dim to bright your HV and crt are ok.
now power off and reconnect just the vert plates.

power back up and select to see only channel 1
put the input selector to GND. on both channels.

now you should be able to move channel 1 vert position up and down and see the trace move from top to bottom.

choose channel 2 for display
gnd the input and move channel 2 vert position up and down and see the trace move from top to bottom.
center the dot and then measure both vert plates…they should be about the same.


power off and disconnect the vert plates.



now do the horizontal….
but first make sure BOTH verts inputs are in GND

reconnect the horz plates….
put time/div to X,Y mode

power up and move the horz position full left then full right
the dot should move full left then full right

center the dot and then measure both horz plates…they should be about the same.

put time/div in 1ms….do you get a line from left to right?

tell me the results of all test .


jim




On Jun 5, 2013, at 7:25 PM, i814u2.geo <fakecrap@> wrote:

Alright, I've been going over this for two nights now and I'm only barely making progress.
Sadly, that's probably because of dumb luck and not any skill/understanding yet.

I tested more transistors or at least made sure things weren't loose. I also swapped one from the B trigger for the one that I found was going bad.
I don't really think that fully helped, but I am starting to at least get the start of a test trace.
It still only shows while pressing the beam finder.

So it does seem like things are working except for the vert amp. Here is where I'm stuck.

This is what I know: schematic shows that pin 9 from U470 (vert amp) should have about 36.6V+ I see 34.3. Pin 12 shows it should have 32.5V+ and I see 32.7.

Not sure how much that matters yet, I just mention it because I measured it and it seemed odd.

Next: I have re-read the suggestions below, from HankC, and I'm honestly lost. I can't see where the board appears to be a folded image of itself. I've stared at the preamp section as well as the amp (which is after the delay line, after the switch, if I understand the diagram correctly).

Here are the answers to HankC's questions, maybe that will help more:
Right now, the power supply readings are within spec. I'm particular and so I'd like them to be closer but they are currently within tolerances. Resistance to ground doesn't match in each case, but right now nothing is completely shorted or completely open.

If I short the delay line, I don't see the trace. If I do it while pressing the beam finder button, it effectively starts to bring the square wave back to a line. Correct me if I'm doing something wrong here.

Things are the same regardless of channel. Pressing invert on CH2 does seem to affect the trace shown with the beam finder. Also, things like triggering work how I would expect, and I can move the trace around (including the angle). I just can't get it to work without the beam finder at this point.

Just so I'm clear, for the shorting process, are you talking about the delay line on the amp board or the preamp board?
Staring at the vert amp board, or the preamp board, I just can't clearly see which section is supposed to be the set of matching sides. I may be looking too literally though.

I just tested U450 for expected voltages and nothing was grossly off. Things were maybe 200 mV off in some cases, but nothing like entire volts off or negative instead of positive. I realize that the mV may still make a difference, but I'm just pointing out that the output sides made sense based on the inputs.

I look forward to some clarification of what board I should test at this point (based on my answers). Also, if I'm doing something wrong, please let me know. I'm anxious to conquer this task and move forward with the next one (as well as furthering my education with this stuff).

Also, if I center the horizontal control, I get voltage readings (at the lines going to the plates) that are not at all as expected (based on the schematic's blue lettering). The left plate is roughly 64.4V (schematic shows 48.1) and the right plate is 34.4V (schematic shows 52.1). I assume that's just an additional issue, not related; again, I'm just adding things I actually know. Odds are high that this will be just another item to review once I can get things up and running and calibrate the machine.

Thanks, as always.

-Josh

--- In TekScopes@..., HankC <hankc918@> wrote:

Josh,

I am jumping onto this thread late & I haven't been following it closely, so you may have already tried what I am about to suggest.

I assume all the power supplies are close to what they should be, or the beamfinder probably wouldn't work.


It sounds like one side of your vert amp is bad, which is driving the trace off screen.
The beam finder restricts the output amp swing so that a trace will occur on-screen if the CRT & high voltage are OK.
Do you get the same result on both channels? Try them one at a time.

If so, then the problem is probably after the vert mode switch (Ch1, Ch2, Add, Alt, etc)
If you select ch2 & then invert it, does the beam finder look the same ?

You can isolate the problem area with a short jumper wire.
The amplifier after the mode switch is usually push-pull, so any unbalance will drive the trace off screen.
You will notice that the top half of the board is a folded image of the bottom half.

You can safely short opposite sides of the amplifier together, NOT to ground or anything else!!
If you short both sides of the delay line together, does the trace return ?
If so, the problem is prior to that point, & probably after the Mode switch.

Working backwards from the delay line, short like points of the prior stage.
Keep working back towards the input until you find the stage where the short has no effect.
That is where you will find your problem.

Usually ( but not always), the case of the transistors is tied to the collector.
So shorting opposing transistor cases together is the easiest way to isolate the problem.



HankC, Boston
WA1HOS

Just to clarify, I only get the dot when pressing the beam finder button, even with all vert/horz plates disconnected. Adjusting the intensity knob did nothing.

Anyway, I re-connected the pins for the vert plates this morning, before work (didn't have much time to spend). Vert plates only, I still see nothing on the screen without the beam finder being pressed.
Now, after maybe 5 minutes (not very long, I realize), the dot would never center. CH1 it was a bit low on the screen and jumped around a bit. CH2 was a bit high on the screen, but stayed in place nicely (although both were a little to the left).

At that point I had to leave for work, but it confused me enough to send this response now. Shouldn't I see a dot without pressing the beam finder at this point? Without the plates being amplified, I would expect to see a dot, but maybe I'm not understanding properly.

I also tested voltages, with vertical adjustment dials centered and everything switched to GND (still vert plates only). They were similar to before and were still off by a few volts.

I hope to work on it more tonight. As always, this help is much appreciated. I'd love to get this up and running. The lady would love that as well (she mistakenly thinks finishing this will get me OUT of the shop).

-Josh

--- In TekScopes@..., Jim Popwell Jr <jpopwell@...> wrote:

ok, the roughly centered dot with NO connections to the deflection plates means the problems are probably with the horz and vertical amps.
find the vertical connections and reconnect the vertical to the crt and run the position test I described.

what happens???
jim


On Jun 6, 2013, at 4:39 PM, "i814u2.geo" <fakecrap@...> wrote:

Disconnected pins for vertical (all 4, to be certain) and desoldered wires for horizontal.
No dot appears, unless I press the beam finder button. Then I get a fuzzy dot roughly in the middle of the X axis (slightly to the left), and roughly half way up the Y axis (assume 0,0 is the center).
Hopefully this doesn't point to a crappy CRT and it tells you something brilliant about a board that I should inspect next.

Again, I'm now anxious for a response to see how much time I've wasted on this thing.
You mention HV as well as CRT, is there any to check which is a common failure? Or do I just go and test whatever the manual provides values for in that area?

Also, I haven't tested voltages that high before, so I'll be researching that first. Any must-read articles/books would be appreciated. Otherwise I'll research what I can do with the gear I have (if anything) and some creative test circuitry. I realize there are some theoretical setups I could build to test a relative value, etc, but I want to know I'm testing safely, not just theoretically.

thanks again

Josh

--- In TekScopes@..., Jim Popwell Jr <jpopwell@> wrote:

Hi Josh,
I'm a little late in looking at this also….so…
turn your intensity down first…. then


power off.

disconnect the vert plates at the crt or vert amp. but be careful the crt pins are very delicate.
this will center the vert beam….

then also disconnect the horz plates….. this will center the horz…..

power on...
adjust your intensity for a easily seen dot about in the center of the crt……not to bright or you could burn the crt…..

if the dot can be seen at the center and can go from dim to bright your HV and crt are ok.
now power off and reconnect just the vert plates.

power back up and select to see only channel 1
put the input selector to GND. on both channels.

now you should be able to move channel 1 vert position up and down and see the trace move from top to bottom.

choose channel 2 for display
gnd the input and move channel 2 vert position up and down and see the trace move from top to bottom.
center the dot and then measure both vert plates…they should be about the same.


power off and disconnect the vert plates.



now do the horizontal….
but first make sure BOTH verts inputs are in GND

reconnect the horz plates….
put time/div to X,Y mode

power up and move the horz position full left then full right
the dot should move full left then full right

center the dot and then measure both horz plates…they should be about the same.

put time/div in 1ms….do you get a line from left to right?

tell me the results of all test .


jim




On Jun 5, 2013, at 7:25 PM, i814u2.geo <fakecrap@> wrote:

Alright, I've been going over this for two nights now and I'm only barely making progress.
Sadly, that's probably because of dumb luck and not any skill/understanding yet.

I tested more transistors or at least made sure things weren't loose. I also swapped one from the B trigger for the one that I found was going bad.
I don't really think that fully helped, but I am starting to at least get the start of a test trace.
It still only shows while pressing the beam finder.

So it does seem like things are working except for the vert amp. Here is where I'm stuck.

This is what I know: schematic shows that pin 9 from U470 (vert amp) should have about 36.6V+ I see 34.3. Pin 12 shows it should have 32.5V+ and I see 32.7.

Not sure how much that matters yet, I just mention it because I measured it and it seemed odd.

Next: I have re-read the suggestions below, from HankC, and I'm honestly lost. I can't see where the board appears to be a folded image of itself. I've stared at the preamp section as well as the amp (which is after the delay line, after the switch, if I understand the diagram correctly).

Here are the answers to HankC's questions, maybe that will help more:
Right now, the power supply readings are within spec. I'm particular and so I'd like them to be closer but they are currently within tolerances. Resistance to ground doesn't match in each case, but right now nothing is completely shorted or completely open.

If I short the delay line, I don't see the trace. If I do it while pressing the beam finder button, it effectively starts to bring the square wave back to a line. Correct me if I'm doing something wrong here.

Things are the same regardless of channel. Pressing invert on CH2 does seem to affect the trace shown with the beam finder. Also, things like triggering work how I would expect, and I can move the trace around (including the angle). I just can't get it to work without the beam finder at this point.

Just so I'm clear, for the shorting process, are you talking about the delay line on the amp board or the preamp board?
Staring at the vert amp board, or the preamp board, I just can't clearly see which section is supposed to be the set of matching sides. I may be looking too literally though.

I just tested U450 for expected voltages and nothing was grossly off. Things were maybe 200 mV off in some cases, but nothing like entire volts off or negative instead of positive. I realize that the mV may still make a difference, but I'm just pointing out that the output sides made sense based on the inputs.

I look forward to some clarification of what board I should test at this point (based on my answers). Also, if I'm doing something wrong, please let me know. I'm anxious to conquer this task and move forward with the next one (as well as furthering my education with this stuff).

Also, if I center the horizontal control, I get voltage readings (at the lines going to the plates) that are not at all as expected (based on the schematic's blue lettering). The left plate is roughly 64.4V (schematic shows 48.1) and the right plate is 34.4V (schematic shows 52.1). I assume that's just an additional issue, not related; again, I'm just adding things I actually know. Odds are high that this will be just another item to review once I can get things up and running and calibrate the machine.

Thanks, as always.

-Josh

--- In TekScopes@..., HankC <hankc918@> wrote:

Josh,

I am jumping onto this thread late & I haven't been following it closely, so you may have already tried what I am about to suggest.

I assume all the power supplies are close to what they should be, or the beamfinder probably wouldn't work.


It sounds like one side of your vert amp is bad, which is driving the trace off screen.
The beam finder restricts the output amp swing so that a trace will occur on-screen if the CRT & high voltage are OK.
Do you get the same result on both channels? Try them one at a time.

If so, then the problem is probably after the vert mode switch (Ch1, Ch2, Add, Alt, etc)
If you select ch2 & then invert it, does the beam finder look the same ?

You can isolate the problem area with a short jumper wire.
The amplifier after the mode switch is usually push-pull, so any unbalance will drive the trace off screen.
You will notice that the top half of the board is a folded image of the bottom half.

You can safely short opposite sides of the amplifier together, NOT to ground or anything else!!
If you short both sides of the delay line together, does the trace return ?
If so, the problem is prior to that point, & probably after the Mode switch.

Working backwards from the delay line, short like points of the prior stage.
Keep working back towards the input until you find the stage where the short has no effect.
That is where you will find your problem.

Usually ( but not always), the case of the transistors is tied to the collector.
So shorting opposing transistor cases together is the easiest way to isolate the problem.



HankC, Boston
WA1HOS

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