Hi all
I know that this is a long shot, as the fault could be from a long list of possibilities, but if someone could have a look in their "crystal ball" for me, it will be greatly appreciated.
The matter concerns a TEK 2246 cro, which has substantial jitter on the displayed waveform, but dies down somewhat after a whlie, but never really stabilises.
The on screen menus however are perfect, just the waveform is jittery.
Could it be a problem with the input amplifier, or perhaps something to do with the vertical deflection?
Any thoughts will be greatly appreciated.
I know that this is a long shot, as the fault could be from a long list of possibilities, but if someone could have a look in their "crystal ball" for me, it will be greatly appreciated.
The matter concerns a TEK 2246 cro, which has substantial jitter on the displayed waveform, but dies down somewhat after a whlie, but never really stabilises.
The on screen menus however are perfect, just the waveform is jittery.
Could it be a problem with the input amplifier, or perhaps something to do with the vertical deflection?
Any thoughts will be greatly appreciated.
I have a question to add as well...
Just bought a nice Leader scope off ~bay, and am having lots of fun with it. HOWEVER, the first five to ten minutes after turning it on scares me. Makes a horrid squealing noise while it warms up. Is this natural? Gets even louder if I turn up the backlight or trace intensity. Within 5~10 gradually becomes quieter until becoming dead silent.
I know CRT scopes need a good warm-up period. Just the (power supply init?) squeal is unnerving.
As for GV's question... I have the opposite, however in a very minimal way. My digital readout can shake a touch depending on the input signal (lock) vs. trace frequency. Takes a short warm-up time to get pretty much unnoticeable. This I think is pretty natural, having to make/sync a second scan for the text.
Your case sounds different, but can you turn off the readout? Might help.
Just bought a nice Leader scope off ~bay, and am having lots of fun with it. HOWEVER, the first five to ten minutes after turning it on scares me. Makes a horrid squealing noise while it warms up. Is this natural? Gets even louder if I turn up the backlight or trace intensity. Within 5~10 gradually becomes quieter until becoming dead silent.
I know CRT scopes need a good warm-up period. Just the (power supply init?) squeal is unnerving.
As for GV's question... I have the opposite, however in a very minimal way. My digital readout can shake a touch depending on the input signal (lock) vs. trace frequency. Takes a short warm-up time to get pretty much unnoticeable. This I think is pretty natural, having to make/sync a second scan for the text.
Your case sounds different, but can you turn off the readout? Might help.
GeeVee said:
It sounds like you need to adjust the triggering. Scopes usually have trigger threshold adjustment knob as well as several switches that deal with selecting polarity, etc. It frequently takes some fooling around with them to achieve a stable waveform, or even to get a trace to appear at all.
I_F
Re: Re: oscilloscope help
Hello and thanks for the response.
Unfortunately it is definately not a triggering or polarity problem.
After some investigation, and assistance by a friend (a self appointed expert!!) the fault is believed to be in the power supply
To make matters worse, the above mentioned problem has now been compounded by another problem.
The CRO now does not display any waveform whatsoever, including the cursors and the on screen text.
This now makes me even more convinced that the problem is in the power supply, or the CRT, or perhaps a combination of both.
Might be easier to replace the entire CRO. They are resonably cheap on ebay now.
Regards
George.
I_Forgot said:
Hello and thanks for the response.
Unfortunately it is definately not a triggering or polarity problem.
After some investigation, and assistance by a friend (a self appointed expert!!) the fault is believed to be in the power supply
To make matters worse, the above mentioned problem has now been compounded by another problem.
The CRO now does not display any waveform whatsoever, including the cursors and the on screen text.
This now makes me even more convinced that the problem is in the power supply, or the CRT, or perhaps a combination of both.
Might be easier to replace the entire CRO. They are resonably cheap on ebay now.
Regards
George.
att'n: be careful to discharge everything first!)update
My oscilloscope is now in pieces on my friends bench, who is far more in the know than I am.
It appears that there are two completely separate problems, which is just coincidence and bad timing.
The first is the power supply. After replacement of most of the electrolytics, the CRT has come back to life, but the subststantial jitter in the waveform is still present.
The second, which is the jitter in the waveform appears to be a triggering problem, as mentioned by I_F.
Therefore I must apologise to I_F for previously dismissing the triggering suggestion so quickly.
I thought that just beceause the trigger light came on, it had satisfactorily captured the signal. No so.
Whilst i am still no wiser as to exactly what the problem / failure is with the jitter, at least the problem has been isolated (fingers crossed)
Regards
GV
My oscilloscope is now in pieces on my friends bench, who is far more in the know than I am.
It appears that there are two completely separate problems, which is just coincidence and bad timing.
The first is the power supply. After replacement of most of the electrolytics, the CRT has come back to life, but the subststantial jitter in the waveform is still present.
The second, which is the jitter in the waveform appears to be a triggering problem, as mentioned by I_F.
Therefore I must apologise to I_F for previously dismissing the triggering suggestion so quickly.
I thought that just beceause the trigger light came on, it had satisfactorily captured the signal. No so.
Whilst i am still no wiser as to exactly what the problem / failure is with the jitter, at least the problem has been isolated (fingers crossed)
Regards
GV
It's not likely to be the CRT. CRTs last a long time. Power supplies croak all the time. That's your starting point.
Jittery waveforms can be the result of noisy pots used to set the trigger threshold (I'm talking about the pot on the front panel with the trigger threshold knob attached to it). Dirty switch contacts in the trigger circuit can cause the same problem. Spray them all with contact cleaner and work them a few times.
I_F
Jittery waveforms can be the result of noisy pots used to set the trigger threshold (I'm talking about the pot on the front panel with the trigger threshold knob attached to it). Dirty switch contacts in the trigger circuit can cause the same problem. Spray them all with contact cleaner and work them a few times.
I_F
End of the Road
After a considerable effort, the problem has been located, and appears that it will be extremely difficult to fix.
The suspect device appears to be the mian trigger microprocessor, designated U500, on board assembly A5.
The U500 is a square 48 pin device, with an integral cooling heatsink.
The test voltages and waveforms surrounding this device are all over the place so to speak.
Unfortunately the service manual indicates that this is not a replaceable part (ie is not listed in section 8 of the service manual as a "replaceable electrical part")
Definately a TEK proprietory item.
Looks like the ony way to fix this is to find a junker, and swap boards.
I hope that this information is of help to anyone else that is experiencing this problem, or witnesses it on a prospective purchase unit.
Regards
GV
After a considerable effort, the problem has been located, and appears that it will be extremely difficult to fix.
The suspect device appears to be the mian trigger microprocessor, designated U500, on board assembly A5.
The U500 is a square 48 pin device, with an integral cooling heatsink.
The test voltages and waveforms surrounding this device are all over the place so to speak.
Unfortunately the service manual indicates that this is not a replaceable part (ie is not listed in section 8 of the service manual as a "replaceable electrical part")
Definately a TEK proprietory item.
Looks like the ony way to fix this is to find a junker, and swap boards.
I hope that this information is of help to anyone else that is experiencing this problem, or witnesses it on a prospective purchase unit.
Regards
GV
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