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| HP 1741A oscilloscope - restoration project |
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| wkb:
Nice job Tekfan! Reminds me of the Tek 2213a that I have sitting here and still needs fixing :( It only displays a partial time base line, like 70% or so of the screen width. Using the x10 on the timebase things get better, like 90% or so. We (a friend of mine and your's truly) were under the impression the CA3046 on the time base module went south but a replacement CA3046 did not help. So more digging to do I'm afraid. It is a nice little scope that I handed down to the aforementioned friend. Initially the time base problem was intermittent, sensitive to gentle tapping. Now it has become a solid fault. Any suggestions maybe? |
| tekfan:
--- Quote from: wkb on December 29, 2011, 05:45:18 pm ---Nice job Tekfan! Reminds me of the Tek 2213a that I have sitting here and still needs fixing :( It only displays a partial time base line, like 70% or so of the screen width. Using the x10 on the timebase things get better, like 90% or so. We (a friend of mine and your's truly) were under the impression the CA3046 on the time base module went south but a replacement CA3046 did not help. So more digging to do I'm afraid. It is a nice little scope that I handed down to the aforementioned friend. Initially the time base problem was intermittent, sensitive to gentle tapping. Now it has become a solid fault. Any suggestions maybe? --- End quote --- First try reseating all the possible connectors in the scope. It may have shorted horizontal output transistors. The gain for the horizontal amplifier might be off due to a wonky trimpot or drifted resistors. When using 10x time base, the gain for the horizontal amplifier is just increased by 10. If one of the driver or output transistors is shorted that may be the cause of the problem. If you have another scope you can use the add both channels and invert one channel trick to get differential inputs and probe around the horizontal amplifier. |
| amspire:
--- Quote from: tekfan on December 29, 2011, 02:19:13 pm ---I've never had any of these fail no matter how dirty or misused the scope was. The primary problem seem to be the shorted rectifiers. --- End quote --- My 1740A was blowing fuses when I purchased it. A new rectifier and it has worked perfectly ever since, so you are right - it does look like those rectifiers are the weak point in the design. I replaced them with larger higher current ones - not pretty, but I hope it is more reliable. Richard |
| tekfan:
Cleaning time for the HP1740A This is how the front panel looks before cleaning And after Now I just have to find a printer or something to rob it of its HP badge Found some cold solder joints on the Z axis amplifier board And this is what happens with a signal at the fastest time base setting This should be a nice sinewave. |
| tekfan:
Since I've got a HP1741A that is very similar to the HP1740A I tought that it would make troubleshooting a bit easier. The upper trace is from a working scope and the lower is from the still defective HP1740A After a bit of searching I found a defective IC. IT contains six separate transistors. I made an adapter so that I can plug it into the curve tracer. And sure enough one transistor was defective. Here is the trace for a good transistor inside the IC I found a discrete transistor with very similar carachteristics as the ones in the IC and soldered it over the IC so that it can be inserted back into the socket. |
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