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#100 Reply
Posted by
vexatag
on 29 Jul, 2020 05:06
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Yes, if I move it from left to right quickly the trace distorts, I wasn't able to capture it on camera but it almost looks like a sine wave or a poorly ramped square wave.
Here's the video.
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#101 Reply
Posted by
bdunham7
on 29 Jul, 2020 05:42
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OK, that isn't a problem. The reason that it distorts is that you don't really have a diagonal line there, you have a rapidly moving dot and persistence of phosphor (and vision) makes it look like a line. When you move it that quickly it can look like that. If you were able to move it quickly and evenly enough, you would even see a coherent waveform. I was concerned with whether there was a stable sort of distortion (bad CRT) or if it moved other than straight back and forth (something really wierd). Since it doesn't do those things, that part is fine and you can proceed with further testing. If it helps, as you are turning the CH2/X volts/div down, you can leave the CH1/Y setting much higher, like 1V/div, if that keeps the line under control.
That diagonal line is noise in the input amplifiers somewhere and it is correlated (in sync) between the two channels. First suspect would be bad power supply caps, so after you do the horizontal deflection tests, you can check the power supply ripple by measuring each power supply voltage on DCV and then ACV. ACV should be really low. I would try both of your meters just to see if you get different results.
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#102 Reply
Posted by
vexatag
on 29 Jul, 2020 06:30
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Results of testing Q808 base with different volts per division:
0.1 v/div: 1.57 to 2.16
50 mv/div: 1.56 to 2.75
20 mv/div: 1.56 to 4.52
10 mv/div: 1.58 to 6.80
Results of testing power supply voltages with the DM383:
5V: 4.93 V DC, 0 V AC
+12V: +12.23 V DC , 0 V AC
-12V: -12.05 V DC, 0 V AC
24V: 24.4 V DC, 0 V AC
140V: 141.8 V DC, 0 V AC
260V: 265 V DC, 0 V AC
Power supply voltages testing, Aneng AN860B+:
5V: 4.935 V DC, 0.000 V AC
+12V: +12.23 V DC, 0.001 or 0.002 V AC
-12V: -12.03 V DC, +0.002 or +0.003 V AC
24V: 24.49 V DC, 0.000 V AC
140V: 142.0 V DC, 0.000 V AC
260V: 265.2 V DC, 0.000 V AC
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#103 Reply
Posted by
bdunham7
on 29 Jul, 2020 14:55
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OK, but we also need to know what happens to D1 and D2 when the base voltage changes on Q808. Just the 20mv/DIV and 10mv/DIV will do. If it changes like it did on the Q809 test the horizontal amp is good.
I thought about your issue with the line getting long and as you are doing the above test, try this. Set X and Y to the same (high) setting so you get that small 45-degree angle line. Then when doing the above test center that line so that it is goes through the center point on the screen with about half above and half below. Then when you do the readings, turn both down together and just let the line get long but only pay attention to the point where it goes thru the horizontal center line. That intersection should move left and right just like the dot would if it weren't all stretched out. Does it do that or does it do something else? If it gets faint or blurry, just turn up the intensity, dim the lights and make your best guess.
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#104 Reply
Posted by
vexatag
on 29 Jul, 2020 23:56
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Right, my bad.
D1 testing:
20 mv/div: 144 V to 96 V
10 mv/div: 144 V to 65 V
D2 testing:
20 mv/div: 155 V to 186 V
10 mv/div: 152 V to 241 V
As for the line, when the test load is applied the entire segment moves up and to the right, even at 5 mv/div.
When checking CH1 in XY mode with a bnc lead in CH2, it's displaying a horizontal line of about the same length as the diagonal line from CH2. Normal mode is still just a trace, but I thought I should point that out.
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#105 Reply
Posted by
bdunham7
on 30 Jul, 2020 00:55
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OK, those numbers look good. As you can see, the plate voltage difference can be driven quite significantly by Q808, so that proves out the horizontal final amp, at least roughly. There are still some gain issues somewhere, but I think we are done in this area for now, as long as your bodge wires hold up and the resistors don't fry entirely. You'll need new ones eventually.
When checking CH1 in XY mode with a bnc lead in CH2, it's displaying a horizontal line of about the same length as the diagonal line from CH2. Normal mode is still just a trace, but I thought I should point that out.
I'm not sure yet what is going on here, and I'm not sure what you mean by 'normal mode is just a trace'. You have a trace in normal mode??? Or is it noise? What happens when you slow down the timebase to 0.1S/div?
So lets look at the input circuits. It is the 'Attenuators and Pre-Amplifier' schematic, followed by 'Vertical Amp and Control Logic'. Something strange appears to be happening here. Try setting the inputs to GRD, XY-mode on, all 4 of the center pushbuttons out, 5mv/div and try to center the dot or whatever is showing. Then reduce the input sensitivity to 10mv/div, and so on. Tell me what you see and make a video if you want--those are helpful--but make sure you get the whole scope face in it so I can see every control.
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#106 Reply
Posted by
vexatag
on 30 Jul, 2020 06:16
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I'm not sure yet what is going on here, and I'm not sure what you mean by 'normal mode is just a trace'. You have a trace in normal mode??? Or is it noise? What happens when you slow down the timebase to 0.1S/div?
Sorry, I used the wrong wording. In non-xy mode, channel 1 is still just showing a single dot.
Here's the video of me testing the inputs. The thing I had the second bnc leads plugged into was just a breadboard with some component leads and pin headers I've been using as a breakout board for slightly more convenient access to the hooks ever since the ends of the hooks got bent out of shape (hook onto the component lead, press the multimeter lead against the pin header).
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#107 Reply
Posted by
bdunham7
on 30 Jul, 2020 14:38
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OK, a couple of things. First, the video did help, but there are two misunderstandings about scope theory that are apparent.
First, I didn't elaborate, but when you switch to the GND, you are disconnecting the inputs internally and shunting the preamplifier to ground. Once you verify that the inputs are unresponsive, you know that that feature is OK and there's no point in supplying any inputs.
Second, in XY mode, those 4 pushbuttons don't do anything. They don't change the channel selection, for example, which I saw you pushing.
You can and should look at the schematics that I referenced and look at the diagrams of at least the switches to see if you can understand how that works.
In any case, we've determined that the problem seems to be on the input side. I also noticed the strange behavior as you were changing the CH2/X attentuator level. It's not uncommon to see a brief jump in the dot as you change ranges, but on CH2/X, it breaks up or jumps at a 45-degree angle--but that channel should only affect horizontal position. So there's some leakage or crossover between channels and it looks roughly equal.
We can also try some testing in the normal, non-XY mode. If you leave the inputs grounded, all 4 pushbutton out and turn XY off, what happens?
Do you have a 9-volt battery, or preferably, several of them? I'd like to try using a larger input signal through the attenuators to try and track down the area where the noise is generated.
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#108 Reply
Posted by
vexatag
on 30 Jul, 2020 20:49
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Very quick comment, I just wanted to say that when the input is set to DC or AC, the channel selection does switch between the two channels. I don't know if they're supposed to or not after what you've just told me but it's the functionality I've been experiencing so far. Also, I do have several 9v batteries lying around.
EDIT: Switching to normal mode with the inputs grounded shifts the dot to the far left of the display, additionally it limits the rightward motion to one square right of center.
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#109 Reply
Posted by
bdunham7
on 30 Jul, 2020 22:07
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Very quick comment, I just wanted to say that when the input is set to DC or AC, the channel selection does switch between the two channels. I don't know if they're supposed to or not after what you've just told me but it's the functionality I've been experiencing so far. Also, I do have several 9v batteries lying around.
EDIT: Switching to normal mode with the inputs grounded shifts the dot to the far left of the display, additionally it limits the rightward motion to one square right of center.
I actually don't know what happens if you push the channel select button in XY-mode, I'd have to look at the schematic. It is possible that it does something like reverse it into YX mode or something weird, but that would be an undocumented feature--or a bug.
So, in normal with the dot to the left try switching one channel at a time from GRD to DC, then one at a time to AC, then both to DC and last both to AC. What happens?
Then, go back to both set to GRD and connect a BNC-to-clip cable to your EXT TRIGGER connection, trigger level centered and knob pulled out, all six pushbuttons out, COUPLING set to DC/LF, SOURCE set to EXT, timebase to the slowest setting (0.2S/div?) and then briefly connect the 9 volt battery to the cable clips, red to positive (the smaller terminal on the battery). If nothing happens, try turning the trigger knob a few degrees clockwise at a time and repeating. If still nothing, try every position of the trigger knob (5 or 6 places).
Next, let's test the vertical amplifiers directly. Turn both channel attenuators counterclockwise to the 5V/div setting. Unground one at a time to the DC setting and give it the same 9 volt input you just did with the trigger. Then do the same in the AC setting. Don't change any other settings the first time, but then push in the second vertical mode button to CH2 and repeat the test on both channels. Lastly, repeat all that except set BOTH channels to DC (you don't need to do AC right now) but run the test one channel at a time, again doing both with the 2nd vertical mode button out, then both with it in.
That seems like a big rigmarole, but we're looking for crosstalk between channels as well as vertical amplifier response. The 9-volt battery should give you a little less than 2 divisions of movement where it moves anything, so a lot more or less than that should be noted.
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#110 Reply
Posted by
vexatag
on 30 Jul, 2020 22:39
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So, in normal with the dot to the left try switching one channel at a time from GRD to DC, then one at a time to AC, then both to DC and last both to AC. What happens?
There is no visual difference between any of these settings in normal mode.
Then, go back to both set to GRD and connect a BNC-to-clip cable to your EXT TRIGGER connection, trigger level centered and knob pulled out, all six pushbuttons out, COUPLING set to DC/LF, SOURCE set to EXT, timebase to the slowest setting (0.2S/div?) and then briefly connect the 9 volt battery to the cable clips, red to positive (the smaller terminal on the battery). If nothing happens, try turning the trigger knob a few degrees clockwise at a time and repeating. If still nothing, try every position of the trigger knob (5 or 6 places).
Nothing at any of the positions on the trigger knob.
Next, let's test the vertical amplifiers directly. Turn both channel attenuators counterclockwise to the 5V/div setting. Unground one at a time to the DC setting and give it the same 9 volt input you just did with the trigger. Then do the same in the AC setting. Don't change any other settings the first time, but then push in the second vertical mode button to CH2 and repeat the test on both channels. Lastly, repeat all that except set BOTH channels to DC (you don't need to do AC right now) but run the test one channel at a time, again doing both with the 2nd vertical mode button out, then both with it in.
I could only get the dot to jump upwards when directly connected to the channel in question (only on channel 1 when the bnc was plugged into CH1, CH1 was set to DC, and the CH1/CH2 switch was not pressed in).
Also, I checked the manual and the four vertical mode switches are in fact supposed to be disengaged when XY mode is engaged. So yes, something is wrong on my end
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#111 Reply
Posted by
bdunham7
on 31 Jul, 2020 04:15
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OK, now we are getting into a tricky area. Give me some time and when I have a chance, I'll look at the schematics and try to figure out how much you can test with what you have. You can have a look at the Trigger and Sweep Generator schematic, and then look at the board for those same parts and just visually check everything and see if there are any more burned parts or physical damage. The circuit in question is very near the previous area that you repaired, so maybe you'll get lucky and spot something.
Basically what I'm looking at is the Trigger and Sweep Generator, along with the Timebase Generator, are pretty much self contained. The LINE and EXT trigger options don't go through the regular channels and they feed the sweep ramp directly to your old friend R834, and we know things are good from there. The operation of the vertical amps in the previous test make me optimistic that those are functioning well enough for now, even though the XY-mode seems to be screwed up.
So, have a look. See if you can find R602, upper left hand corner of the Trig/Sweep schematic, near the trigger source switch. See if you can verify that there is -12V on both sides of it.
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#112 Reply
Posted by
vexatag
on 31 Jul, 2020 05:08
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Found R602, it's either near or in the repair job someone else had done. There's no obvious charring or anything to make me think it was damaged. The side connected to ground measured -12V, but the other side measured -9.36V. Checking the resistance, it's 4.68k ohms, so the drop is probably coming from somewhere else in the circuit?
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#113 Reply
Posted by
bdunham7
on 31 Jul, 2020 14:54
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That seems OK, although if you switch the SOURCE to ALT, the drop should go away and both sides would be -12V.
So we're headed into a tricky section here, especially since there could be some variance between the schematic and your circuit board due to the different versions I alluded to much earlier. It hasn't happened yet, but it is one more thing to worry about. I'm still pondering how to test this without another scope, but there are a few things you should check first just so we don't miss something simple.
The upper left portion (on the schematic, not the board) of the Trig & Sweep Generator schematic is the basic input switching part. You can follow a 9V input into the EXT input through the switches all the way to the SLOPE switch S603, and you can do that with the power off. See if you can figure out how to do that just looking at the schematic. On the BK2120 I had, the COUPLING and SOURCE switches were damaged and bent from some unknown abuse, but straightening them out seemed to fix them, so that is one of the first things to check.
Next, those bodge wires near this area. It occurred to me that they might be some sort of unsuccessful repair or modification or patch, instead of an actual repair that worked. Can you look carefully at those wires and tell me exactly where they are attached in the schematic? Is there any other damage to the board, or missing parts or
Last, let's have a quick look at the LINE trigger option. If you see the input on the left edge marked FROM BD503, LINE 60HZ, find that point on the board and R610. This is power on--you should have an AC voltage on both sides of R610 and then the same voltage at the upper center terminal (on the schematic--you have to find where this is on the switch) of S603. The voltage will only be at S603 when the COUPLING switch is in LINE, so you can differentiate it from noise by turning the switch from LINE to some other setting and back (slowly--AC readings take time to settle) and so on. The LINE signal will be attenuated at each step through the system, so don't worry if it is lower as you go along--just see if it is there and comes and goes in response to the switch.
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#114 Reply
Posted by
vexatag
on 31 Jul, 2020 23:39
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The upper left portion (on the schematic, not the board) of the Trig & Sweep Generator schematic is the basic input switching part. You can follow a 9V input into the EXT input through the switches all the way to the SLOPE switch S603, and you can do that with the power off. See if you can figure out how to do that just looking at the schematic. On the BK2120 I had, the COUPLING and SOURCE switches were damaged and bent from some unknown abuse, but straightening them out seemed to fix them, so that is one of the first things to check.
Somewhat confused as to what you mean by this, hook the battery up to the ext port and check for voltages at each component in the circuit? It's been a hot day and my motivation has been low, but I'll remove the circuit board and try to figure out the bodge job. I can't find R610 on either the Trig and Sweep Generator schematic or anywhere on the circuit board.
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#115 Reply
Posted by
bdunham7
on 01 Aug, 2020 00:18
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Yes, just connect the battery to the EXT trigger BNC with your handy cables, switch the mode to EXT and then follow the trail as far as the slope switch with your DMM in the usual way. If the board is out, you'll have to find a ground point, but the BNC or battery negative should do fine. And you can change the switch back and forth from EXT to ALT to make sure your battery signal comes and goes.
As far as motivation goes, you've been working on that thing for a while. I'll still be here later if you want to give it a break for now!
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#116 Reply
Posted by
bdunham7
on 01 Aug, 2020 00:40
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I can't find R610 on either the Trig and Sweep Generator schematic or anywhere on the circuit board.
R610 on the schematic is on the left side right next to the "FROM BD503 LINE 60 HZ". It is all run together as R61027K. I don't see in on your board either, nor on the board diagram in the manual, but it should be connected to R611 and might be off-board or connected by a wire. It should be near a wire coming from the power supply---if you look at that schematic you'll see it coming off of the top of bridge rectifier BD603--'to R610'.
I've noticed the first version discrepancy--the trigger op amp U601 in the manual is U615 on your board. There might be more, so if you see anything clearly different let me know.
EDIT: R610 is on the low voltage power supply board.
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#117 Reply
Posted by
vexatag
on 01 Aug, 2020 07:42
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Re: I've been working on this a while, it's the sort of thing where if I set it down I won't take care of it for many many months, this thing is big enough that I want it to be working
I've noticed the first version discrepancy--the trigger op amp U601 in the manual is U615 on your board. There might be more, so if you see anything clearly different let me know.
Weirdly, U615 is also called U601 on the opposite side of the PCB.
Voltages for each part I could find in the circuit, listed in the order I tested them. Some are probably only used for other triggering modes but I tested them anyway. I tested with the coupling switch set to DC/LF and the source set to ext, I was able to have the board out with everything except the CRT inputs plugged in. All numbers are in volts, none of that mv rubbish.
Battery voltage: 9.39
Voltage at the switch: 9.16
R601: 9.16 to 9.37
C601: 9.16 to 9.37
R602: 0.00 and 0.00
R605: 9.16 to 9.08
R603: 9.16 to 0.00
R606: 9.09 to 4.745
C603: 9.16 to 0.482
R604: 0.199 to 0.00
R607: 0.200 to 0.200
C630: 0.415 to 0.417
R609: 4.024 to 4.804
C604: 9.08 to 4.787
C606: 4.097 and 0.00
I went ahead and checked the resistance of the resistors that had an input voltage of ~9V and an output voltage of 0V, all were within spec.
The other testing will happen tomorrow.
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#118 Reply
Posted by
vexatag
on 01 Aug, 2020 22:40
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R610 measured at 7.3 V and 1.67 V AC, I also found two points on S603 that measured 1.67 V AC only when the coupling was set to LINE.
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#119 Reply
Posted by
bdunham7
on 02 Aug, 2020 15:56
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OK, remember those two points, that is the input side of the switch.
So I think the next thing to do is make a test tool. You'll need a 9 volt battery, a clip or something to reliably wire to the battery (I snip them off of dead or obsolete devices) and the 10K potentiometer you said you had earlier. Wire up the 9 volt battery to the outside (fixed) terminals of the potentiometer, then attach one wire to the center (variable) tap and one to the side where the negative battery lead went. You should now have a short-circuit proof variable voltage source, which you can confirm with your voltmeter. It might be worthwhile to take the time to make the whole thing neat and durable.
Next, connect it to the EXT trigger in with DC/LF/TV-V and try to find a signal right where you found the AC signal on S603. If everything works, you should be able to turn your pot up and down and see the voltage change in sync at the center input terminal of S603.
Last for now, move your voltmeter lead to the switch terminal exactly opposite of wherever you find your signal in the last step. By 'opposite', I mean in the other row--there's two rows of 4 or 5 terminals, same postion/opposite row. Then, with the scope turned on and the trigger level knob not it AUTO (pulled out), you should be able to turn it up and down and see a similar change in voltage at that point. These are the inputs to U601 (or U615??) which is the trigger comparator--it turns on when the voltage on the input side exceeds the voltage on the trigger level side--or vice versa if SLOPE (-) is selected.
The rest of the trigger logic circuit is more complicated and I'm still trying to figure out a way to have you test it with what you have on hand.
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#120 Reply
Posted by
vexatag
on 02 Aug, 2020 21:06
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I've also got an eight-AA holder if that'd maybe work better? The only 9v clip I have to sacrifice is on the 1khz signal generator and I'd hate to sacrifice it.
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#121 Reply
Posted by
bdunham7
on 02 Aug, 2020 21:18
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Yes that should work. 10 x 1.5V =12V. 12V thru 10K pot = 1.2mA, 14.4mW dissipation. But you need 8 AA cells, I suppose the Sunbeam ones from a dollar store will work.
Tell me more about this signal generator, like output specs and so forth. It might be handy.
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#122 Reply
Posted by
vexatag
on 02 Aug, 2020 21:31
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The holder actually has eight rechargeable AAs in it, I've been using it to power a 140mm PC fan I've been using to extract rosin fumes when soldering. It has a standard 5.5mm DC barrel jack, so hooking it to the pot should be easy enough. (and yes, I've got 5.5mm barrel jacks for the receiving end, I purchased a twenty pack with ten of each for an earlier project)
The signal generator is a
Velleman MK105, I believe I mentioned it earlier in the thread as one of my resources.
EDIT: I hooked the positive line to pin 1 and the negative line to pin 3, next I hook up a wire connecting pin 2 to pin 3?
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#123 Reply
Posted by
bdunham7
on 04 Aug, 2020 00:16
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Your output wires will be pin 2 (+) and pin 3 (-). Try it on a voltmeter.
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#124 Reply
Posted by
vexatag
on 04 Aug, 2020 06:43
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I totally misunderstood how potentiometers work, whoops. The only thing I added was component leads on 2 and 3 to give my garbage scope probes something to hook onto.
Next, [...] right where you found the AC signal on S603. If everything works, you should be able to turn your pot up and down and see the voltage change in sync at the center input terminal of S603.
[...] By 'opposite', I mean in the other row--there's two rows of 4 or 5 terminals, same postion/opposite row. Then, with the scope turned on and the trigger level knob not it AUTO (pulled out), you should be able to turn it up and down and see a similar change in voltage at that point. These are the inputs to U601 (or U615??) which is the trigger comparator--it turns on when the voltage on the input side exceeds the voltage on the trigger level side--or vice versa if SLOPE (-) is selected.
I did the tests you asked me to and was able to get AC voltage changes on both pins.
Side note, I did find four three digit voltmeter modules from a previous project (rated at 2.6-30V according to the packaging), so that's a cool thing (or would be if they cooperated with the 10k pot, I hooked one up to pin 2 and 3 but it didn't respond correctly, the display dimmed at 2.35 v with the pot mostly closed but cut out at 3.5 with the pot mostly open. It's something I'll need to look at further later I think).