| Electronics > Repair |
| BK Precision 2120 trace issues |
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| vexatag:
In quite possibly the most foolish decision I'll make all year, I bought a broken BK 2120. There are some dents on the chassis that the seller didn't do a good job of pointing out, one of the feet on the back is cracked off, and several screws are missing from the bottom of the chassis. The main issue, however, is the trace. Both channels behave identically. When hooked up to the calibration point, they show two shimmering ~7mm lines ~3mm apart from each other. The x position knob turned all the way left is off screen, but turned all the way right is dead center. Shifting this rapidly back and forth does reveal some amount of waveform. Here is a link to the pictures I took this afternoon after unpacking it. If there are any other diagnostic steps I should take before poking with a multimeter please let me know. |
| med6753:
--- Quote from: vexatag on July 11, 2020, 10:13:14 am ---In quite possibly the most foolish decision I'll make all year, I bought a broken BK 2120. There are some dents on the chassis that the seller didn't do a good job of pointing out, one of the feet on the back is cracked off, and several screws are missing from the bottom of the chassis. The main issue, however, is the trace. Both channels behave identically. When hooked up to the calibration point, they show two shimmering ~7mm lines ~3mm apart from each other. The x position knob turned all the way left is off screen, but turned all the way right is dead center. Shifting this rapidly back and forth does reveal some amount of waveform. Here is a link to the pictures I took this afternoon after unpacking it. If there are any other diagnostic steps I should take before poking with a multimeter please let me know. --- End quote --- I have a 2120 in my collection of scopes which obviously is in much better condition than that one. That's really been beat up. Anyway, if you don't have the service manual download one. Make sure it's the service manual and not the user manual. There are plenty of on line sources. Start with the basics. All power supply voltages must be present. Then take it from that point. |
| bdunham7:
Has anyone pushed that XY button yet? Did you ask the seller to do that and if so, what happened? If pushing the button and setting the trigger to AUTO doesn't give you a trace, you know the horizonatal sweep isn't working--and that's a bad thing. Also, do you look at eBay auctions on your phone or on a computer. I saw that damage in the eBay photos, at least the cracked back part. You're going to have a tough time. the BK2120 was made in several iterations (not including the explicitly different A, B, versions, etc) and it is likely that what you have in front of you will not exactly match the manuals and schematics that are available. The first thing would be to take the covers off and examine it for physical damage. Beware that although it is not an accelerated CRT, there is still a good -1500VDC at the gun and many hundreds of volts elsewhere, and then there's mains voltages in certain places. |
| vexatag:
--- Quote from: med6753 on July 11, 2020, 03:07:12 pm ---I have a 2120 in my collection of scopes which obviously is in much better condition than that one. That's really been beat up. Anyway, if you don't have the service manual download one. Make sure it's the service manual and not the user manual. There are plenty of on line sources. Start with the basics. All power supply voltages must be present. Then take it from that point. --- End quote --- The first thing I did after buying this was download the service manual from one of your posts here. I'll check the voltages this evening (Pacific time) and report back. --- Quote from: bdunham7 on July 11, 2020, 05:50:58 pm ---Has anyone pushed that XY button yet? Did you ask the seller to do that and if so, what happened? If pushing the button and setting the trigger to AUTO doesn't give you a trace, you know the horizonatal sweep isn't working--and that's a bad thing. --- End quote --- Pressing the XY button moves what's displayed over a centimeter or two, no actual change in the trace generation. --- Quote from: bdunham7 on July 11, 2020, 05:50:58 pm ---Also, do you look at eBay auctions on your phone or on a computer. I saw that damage in the eBay photos, at least the cracked back part. --- End quote --- I look at auctions on my computer, there's no excuse for my lack of diligence here :-[ --- Quote from: bdunham7 on July 11, 2020, 05:50:58 pm ---You're going to have a tough time. the BK2120 was made in several iterations (not including the explicitly different A, B, versions, etc) and it is likely that what you have in front of you will not exactly match the manuals and schematics that are available. --- End quote --- Is there any easy way you know of to check which version it is? --- Quote from: bdunham7 on July 11, 2020, 05:50:58 pm ---The first thing would be to take the covers off and examine it for physical damage. Beware that although it is not an accelerated CRT, there is still a good -1500VDC at the gun and many hundreds of volts elsewhere, and then there's mains voltages in certain places. --- End quote --- I understand and appreciate the advice. |
| vexatag:
Update: Took off the casing, no damage to the PCB amazingly enough. 140v test point is reading 141 on my DMM, 260v test point is only reading 79-83v. I can't test the 2kv test point unfortunately. I also went ahead and tapped the bottom of the case more flat, I want to sand it to bare metal and repaint it, question is what color is closest. |
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