BK Precision CRT tester (470) - Videokarma.org TV - Video

TinCanAlley · #1 11-08-2021, 04:27 PM

Okay, I don't know if I'm having issues with this unit, or the socket is wrong.

I'm trying to test a monochrome CRT out of an IBM 5151 monitor from 1982. The tube number is quite long, but just using the first 5 from it I found a match in the testers list and it is the socket that fits. It is a 7 pin socket and the only one small enough and with the correct pins. I hooked it up, dialed in the heater voltage, meter showed 12V and the heater lit up. I then check for shorts, nothing. I then raised the G1 voltage to 50V and meter showed that voltage. I then tried setting the G2. This is where I have the problem. The manual says to turn the G2 until the needle raises ONE DIVISION. Now I am assuming that from 0 on the meter they mean until it move one marking. Only issue, the needle does not move. I know the monitor wants 270V on G2, so I'm assuming the tester should be providing around that. When I put the control to max, the needle hasn't moved, but when I press the emission button, it move to the GOOD range. If I hold it and reduce the control, the needle moves down.

Is there an issue with the unit or could the socket have a pin or two wrong? I know the heater pins are correct. If I were to probe the socket with a meter, which pin should I use as ground? I don't know if the heater ground is safe as I believe the heater and the other pins use different voltage types (DC and AC). So I want to measure pin 6 that is supposed to be G2 and I will use the red DMM lead. Where do I connect the black lead? Also, I don't plan on cranking up the G2 to blow my DMM, just enough to see if the knob causes an increase on the socket.

Thanks!

TinCanAlley · #2 11-08-2021, 05:12 PM

After another search I managed to find the schematics and such for the tester. It gave me the wiring diagram for the cable that connects to the various sockets. From there I was able to match up the socket to the cable and found that one of the wires is oddly out of place (or at least it is to my thinking).

I am attaching the pinout and voltages of the CRT and am hoping someone will tell me which voltage is which on pins 5 and 2. I know one is G1, but is that the negative voltage or the positive? On the socket, the G1 (-53.3V)is connected to the CRT on pin 5 and the K (53.7V) is connected to pin 2 of the CRT. If those are correct, then the only issue is the socket has the G2 (RED) connected to the G2 (GREEN) of the cable. It should be on the G2 RED as that's the adjustment for monochrome/BW tubes.

So I need to pull the pin out of the connector and move it from 10 to 9 so red G2 is connected to the CRT.

TinCanAlley · #3 11-08-2021, 06:46 PM

Well I moved the connection in the socket adapter from 10 to 9 and I still can't get the meter to move when adjusting G2. So either the unit has a problem, or pin 2 and 5 are reversed? I don't know. I really can't do any other testing as the monitor will not display even a raster when not connected to a source and my monochrome adapter hasn't arrived. The best I was able to do was plug it in and see no sparks and that the heater element is glowing. Beyond that, I don't know what else to do.

Notimetolooz · #4 11-09-2021, 09:19 AM

You really haven't given enough of the info someone would need to figure this out.
First of all don't go changing the tester to fit what you think the connection should be for this CRT. You will spoil it for other CRTs.
You haven't told what the CRT number is or what number CRT you chose in the table that you intend to use. Choosing a setup because some of the digits match is probably not good enough.
How about posting the schematic of the tester.
CRT testers don't put the same voltage on the tube as that when the tube is in use. The voltages are selected to give the proper reading on the tester.

For no raster you could just measure the voltages the monitor puts on the tube vs. what the monitor schematic indicates to determine if the CRT is functioning.
Yes you may need to get a HV probe.

TinCanAlley · #5 11-09-2021, 04:52 PM

Quote:

Originally Posted by Notimetolooz

You really haven't given enough of the info someone would need to figure this out.
First of all don't go changing the tester to fit what you think the connection should be for this CRT. You will spoil it for other CRTs.
You haven't told what the CRT number is or what number CRT you chose in the table that you intend to use. Choosing a setup because some of the digits match is probably not good enough.
How about posting the schematic of the tester.
CRT testers don't put the same voltage on the tube as that when the tube is in use. The voltages are selected to give the proper reading on the tester.

For no raster you could just measure the voltages the monitor puts on the tube vs. what the monitor schematic indicates to determine if the CRT is functioning.
Yes you may need to get a HV probe.

What else would you like? I put up pics of the socket, pic of the CRT neck pins and their voltage and what each wire of the plug on the tester is using. If the tester says to use that socket adapter for a B&W or monochrome monitor, and to adjust only the red settings of the tester, then having the blue or green conntected for G2 is a mistake as there would be no way to adjust the G2 with the wrong lead on it.

I used the tester's service manual to find the pinout and wire colors.

The CRT I am testing is from and IBM Monochrome monitor. The tube number is: CE751Z12P29ZRV. The only monochrome monitor on the list from B&W is: CE751 and that is the first 5 places of the tube number. It is also a 7 pin (small diameter).

I'm not worried about messing up the wiring on the adapter as I have 2 of that number. Also, I could always cut all the wires and make it rewireable for other types of CRTs.

I have attached the schematics of the tester.

Electronic M · #6 11-09-2021, 06:12 PM

You may want to avoid running the monitor until you check one thing...
This wasn't the case with all IBM monitors, but I've heard some of the early IBM monitors didn't have an on board horizontal and vertical oscillator...That means if you power them on without horizontal and vertical sync signals from the PC the monitor will destroy it's self in a few moments.

I'm not a computer collector but I know enough people who are to have heard of this issue.

Notimetolooz · #7 11-09-2021, 11:04 PM

I guess you are questioning whether the tester is function correctly or whether your hookup is correct.
Have you used this tester successfully on a CRT recently?
A main problem is that you don't really know which CRT pin is which on this tube. Just because the CRT number is similar to the one in the book does not mean you have the socket connected correctly, or the voltages correct.

After studying the tester schematic it seems the emission is tested with the cathode and G1 connected together and using the voltage on G2, the meter reading being related to the current flowing.
Many times the cut-off bias is based on the G1 voltage required to cut off the cathode current using a set G2 voltage, similar to the way a CRT is actually operated. This tester uses a set G1 voltage and finds the G2 voltage that results in the current decreasing.
The voltage are with respect to the cathode voltage by the way.

I still think the best approach is to measure the socket voltages in the monitor, since you know what they should be. If those voltages are correct and you have no raster then the CRT is at fault. The monitor socket voltages most probably should be with respect to the monitor circuit ground. From your posted info I could guess that the CRT pin 2 is the cathode and pin 5 is G1. Whether pin 6 or 7 is G2 I don't know.
You are aware I suppose that many monitors blank the screen when they do not receive the proper signals from a computer, in that case one or more voltages would be very different.

TinCanAlley · #8 11-09-2021, 11:30 PM

Quote:

Originally Posted by Electronic M

You may want to avoid running the monitor until you check one thing...
This wasn't the case with all IBM monitors, but I've heard some of the early IBM monitors didn't have an on board horizontal and vertical oscillator...That means if you power them on without horizontal and vertical sync signals from the PC the monitor will destroy it's self in a few moments.

I'm not a computer collector but I know enough people who are to have heard of this issue.

You are correct. The monitor needs a horizontal signal to work, but they don't die if not connected, at least not in my experience. I worked with so many of them in the early to mid 80s and never lost one to applying power without an H signal. With out the H signal on the base of the HOT, it pretty much just sits there. My monochrome adapter died and the replacement never got shipped (they claim to have misplaced it). So now I have to find another suitable replacement so I can get the thing a signal for full testing.

TinCanAlley · #9 11-09-2021, 11:44 PM

Quote:

Originally Posted by Notimetolooz

I guess you are questioning whether the tester is function correctly or whether your hookup is correct.
Have you used this tester successfully on a CRT recently?
A main problem is that you don't really know which CRT pin is which on this tube. Just because the CRT number is similar to the one in the book does not mean you have the socket connected correctly, or the voltages correct.

After studying the tester schematic it seems the emission is tested with the cathode and G1 connected together and using the voltage on G2, the meter reading being related to the current flowing.
Many times the cut-off bias is based on the G1 voltage required to cut off the cathode current using a set G2 voltage, similar to the way a CRT is actually operated. This tester uses a set G1 voltage and finds the G2 voltage that results in the current decreasing.
The voltage are with respect to the cathode voltage by the way.

I still think the best approach is to measure the socket voltages in the monitor, since you know what they should be. If those voltages are correct and you have no raster then the CRT is at fault. The monitor socket voltages most probably should be with respect to the monitor circuit ground. From your posted info I could guess that the CRT pin 2 is the cathode and pin 5 is G1. Whether pin 6 or 7 is G2 I don't know.
You are aware I suppose that many monitors blank the screen when they do not receive the proper signals from a computer, in that case one or more voltages would be very different.

I do know the pinouts of the CRT, I attached the info in my post. I know 7 is G4, 6 is G2, 3 and 4 are heater, and 1 isn't used. That leave 2 and 5. If G1 is a negative voltage, then it has to be pin 5. That would leave pin 2 as cathode, I'm assuming.

The pins of the tester's socket match up all but the G2 as it was connected to the blue control on the tester's end. This makes the manual's instructions of using the red controls for B&W / monochrome CRTs useless. The R, G and B controls have to be independent or color CRT testing wouldn't be possible.

I have one more monochrome CRT in a TRS-80 Model 4 that I will try and find in the CRT list for the tester. If it is, and is socket 7 as well, I will compare the pinouts of the CRT to the tester.

Notimetolooz · #10 11-10-2021, 10:03 AM

It wasn't clear from your earlier posts what info was known for sure or whether it was from assumptions.
It wasn't clear from the pictures what color wire went to which locations in the rectangular connector or how the connector pins were numbered.
I can state categorically that your assumption that the tester uses the same voltages on the pins as the monitor is wrong. The tester makes no attempt to light up the screen which is the whole point of much of the monitor circuits, HV is not applied for instance. I suppose you have some documentation that the heater voltage should be 12V.
Your assumption that you should use the same settings for this CRT as those found in the tester info may or may not to correct.
During the emission test the tester connects the cathode and G1 together which means the G1 voltage isn't used at all.
As you noticed you could make the emission reading good or bad just by changing the G2 voltage setting.
If you used the tester successfully before that would help rule out operator error on the cutoff test, it isn't clear you answered that question.
The two faults common on old monitor CRT are emission and burnt phosphor screen.
The good news is that the emission test is working, you just don't know the results are accurate. If G2 is not connected I don't see how the emission test would work correctly, maybe G3 or G4 is connected instead because the wiring is incorrect. This tester wouldn't give you any idea about the screen anyway.
Does the monitor info that shows the socket voltage indicate whether the voltages apply with a good signal to the monitor or without input signals?
The voltages may apply to the case without signals in which case the screen might be blanked, the cathode-G1 bias looks like it may be that way.

TinCanAlley · #11 11-10-2021, 12:29 PM

Quote:

Originally Posted by Notimetolooz

It wasn't clear from your earlier posts what info was known for sure or whether it was from assumptions.
It wasn't clear from the pictures what color wire went to which locations in the rectangular connector or how the connector pins were numbered.
I can state categorically that your assumption that the tester uses the same voltages on the pins as the monitor is wrong. The tester makes no attempt to light up the screen which is the whole point of much of the monitor circuits, HV is not applied for instance. I suppose you have some documentation that the heater voltage should be 12V.
Your assumption that you should use the same settings for this CRT as those found in the tester info may or may not to correct.
During the emission test the tester connects the cathode and G1 together which means the G1 voltage isn't used at all.
As you noticed you could make the emission reading good or bad just by changing the G2 voltage setting.
If you used the tester successfully before that would help rule out operator error on the cutoff test, it isn't clear you answered that question.
The two faults common on old monitor CRT are emission and burnt phosphor screen.
The good news is that the emission test is working, you just don't know the results are accurate. If G2 is not connected I don't see how the emission test would work correctly, maybe G3 or G4 is connected instead because the wiring is incorrect. This tester wouldn't give you any idea about the screen anyway.
Does the monitor info that shows the socket voltage indicate whether the voltages apply with a good signal to the monitor or without input signals?
The voltages may apply to the case without signals in which case the screen might be blanked, the cathode-G1 bias looks like it may be that way.

The schematics for the monitor show the heater getting 14.9V, but the tester only goes up to 14. I settled on 12 as the base, but put it as high as 14.

I was under the assumption that the tester could provide up to 450V for G2? Their next model up has a setting for 300V or 600V G2.

I know the unit doesn't provide the HV necessary to light up the CRT.

I used it last on a CRT in a Zenith Avante and it worked as expected. Each color gun was set using their respective G2 control. Each one moved the needle up one division on the meter. So at that time, the unit was working correctly. I can't guarantee it is still working, but I guess I could connect it back to the Zenith and verify.

Yeah, the pic of the connector was more for a visual of what the connector looked like. In the pic you can see the metal pins and on the bottom row (with just 2 pins), one is location 10, when that pin should be in location 9.

The tester manual says that all B&W tubes as well as projection should use the G2 control marked RED/B&W. I emailed BK and they said all monochrome CRTs use that single G2 control. Too bad the person couldn't explain the socket wiring issue, but they haven't made or truly support these things for a number of years.

Notimetolooz · #12 11-11-2021, 09:01 AM

OK. It could very well be that the monitor and CRT were made after the tester was made, so the data on that CRT was not included in the setup info.
That also includes which adapter to use, although I think you said that the adapter called for was not one that you had therefore you wanted to move a pin on the adapter.
Several CRT testers I am familiar with test cut off by starting with the emission on and G1 at zero with the G2 set and then increase the negative G1 until the emission is cut off. This one starts out with the emission cut off, with some G1 bias and increases the G2 voltage until the emission starts. Either way tests the tube, but the numbers are different. A cut off value has more to do with gray levels and contrast on a TV tube than a computer monitor tube.
Chances are that the CRT emission is good (enough) on that tube.
If you are getting no raster the problem is likely the monitor.

TinCanAlley · #13 11-11-2021, 04:05 PM

Quote:

Originally Posted by Notimetolooz

OK. It could very well be that the monitor and CRT were made after the tester was made, so the data on that CRT was not included in the setup info.
That also includes which adapter to use, although I think you said that the adapter called for was not one that you had therefore you wanted to move a pin on the adapter.
Several CRT testers I am familiar with test cut off by starting with the emission on and G1 at zero with the G2 set and then increase the negative G1 until the emission is cut off. This one starts out with the emission cut off, with some G1 bias and increases the G2 voltage until the emission starts. Either way tests the tube, but the numbers are different. A cut off value has more to do with gray levels and contrast on a TV tube than a computer monitor tube.
Chances are that the CRT emission is good (enough) on that tube.
If you are getting no raster the problem is likely the monitor.

There is only one adapter for use with the small diameter 7 pin tubes, I verified with BK. The problem with the adapter is the G2 is connected to the test via the pin for green G2, not red G2 as required for BW and Monochrome PC CRTs. They couldn't explain why. So I pulled the wire from the plug's #10 and moved to #9 so the red G2 knob would be as expected. I could have left it as is and used the green, but I figured why have to remember years from now if I go to use it again.

Yeah, the monitor has no H generator, so the HV stays off until it gets one. I will have to wait until I can connect it to the PC as I am awaiting a new adapter.

Electronic M · #14 11-11-2021, 04:37 PM

If you know the H frequency (or the refresh rate and resolution which can be used to calculate it) and the drive signal amplitude and have a function generator that can produce a square wave of the right amplitude frequency and duty cycle then you could potentially get the monitor to produce a raster....If you achieve that you could get a rough idea of emissions and cutoff over signal range by hooking up a NTSC composite video source to the video pins (it won't be in sync but would give grayscale a check).

TinCanAlley · #15 11-12-2021, 12:58 AM

Quote:

Originally Posted by Electronic M

If you know the H frequency (or the refresh rate and resolution which can be used to calculate it) and the drive signal amplitude and have a function generator that can produce a square wave of the right amplitude frequency and duty cycle then you could potentially get the monitor to produce a raster....If you achieve that you could get a rough idea of emissions and cutoff over signal range by hooking up a NTSC composite video source to the video pins (it won't be in sync but would give grayscale a check).

I believe the H is 18.432kHz and V is 50Hz. Wish I had a way to generate the signal. Might be nice to have one for future, but the video card will be here before I could get a generator.