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#1
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Sick Scope
My Tek 466 scope decided to misbehave. It will not display the horizontal
beam unless I press the beam finder. When I do it displays whatever I'm looking at(eg: 7 Mhz sine wave) properly. I'm quite familiar with this scope, but possibly doing something stupid. Does anyone have any idea as to what the problem could be? Thanks in advance for any light you can shed on the problem. Laurie |
#2
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Laurie:
There are really several possible problems you may be encountering. Positioning is one, another may be gain... Beam finder centers the display so you can see you have a trace active. In most models, it also temporarily switches the scope to auto trigger. Most likely, you have the horizontal or vertical position maladjusted to put the display way off the screen... Try centering the horizontal and vertical position controls and see if you can see the trace. If you set the trigger to Auto, you should see a trace on the display even if there is no signal applied. Also, when you press the beam finder, if you watch closely, you may notice which direction the displayed waveform came from, or the direction it goes when you release the beam finder button. This can give you an idea of which of the position controls you need to adjust. If you have the position controls centered and the trace isn't somewhere near center, check the DC/AC signal switch. If you have it set to AC, it should be centered if the display position controls are somewhere near centered. If the input signal is DC coupled, and there is a significant DC offset to the signal, it can be off screen. Changing the coupling to AC will help to center the trace on the display. Gain could also be a problem. If you have the vertical gain set too high, even if the display is centered, the trace is spread out so far vertically that it can be nearly invisible. Still no joy? To set the scope to a known state, set Coupling to AC, center the horizontal position controls, and set the trigger to auto. Turn up the display brightness (not the graticule illumination) and you should see a single horizontal line (trace) somewhere near the vertical center of the display. Add an input signal and you should see a change in the trace. Adjusting the time base and trigger level should allow resolving the trace to a stable display. Nearly everyone has lost a trace in the history of their scope use, been there, done that myself a time or two, especially when in a hurry.... --Rick AH7H Laurie Landry wrote: My Tek 466 scope decided to misbehave. It will not display the horizontal beam unless I press the beam finder. When I do it displays whatever I'm looking at(eg: 7 Mhz sine wave) properly. I'm quite familiar with this scope, but possibly doing something stupid. Does anyone have any idea as to what the problem could be? Thanks in advance for any light you can shed on the problem. Laurie |
#3
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Rick & Joe,
Thanks for your suggestions, however, all of your mentioned items have been checked, and I am quite confident that the problem lies inside the box. I now have a 333 page service manual...that unfortunately is more oriented towards callibration than troubleshooting...but may lead to some useful information. Laurie |
#4
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Rick & Joe,
Thanks for your suggestions, however, all of your mentioned items have been checked, and I am quite confident that the problem lies inside the box. I now have a 333 page service manual...that unfortunately is more oriented towards callibration than troubleshooting...but may lead to some useful information. First thing I'd suggest checking on a scope of this vintage is the power supply bypass capacitors. See if there's excessive AC ripple on any of the DC supply lines - if so, one of the 'lytic capacitor cans has probably dried out and gone high-Z. All sorts of interesting symptoms can occur as a result. Exact-replacement caps are likely to be impossible to find - you may very well need to improvise, using a modern 'lytic of equal or greater capacity and WVDC rating, and some creative wiring and mounting arrangements to adapt the new cap(s) to the old pinouts. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
#5
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Rick & Joe,
Thanks for your suggestions, however, all of your mentioned items have been checked, and I am quite confident that the problem lies inside the box. I now have a 333 page service manual...that unfortunately is more oriented towards callibration than troubleshooting...but may lead to some useful information. First thing I'd suggest checking on a scope of this vintage is the power supply bypass capacitors. See if there's excessive AC ripple on any of the DC supply lines - if so, one of the 'lytic capacitor cans has probably dried out and gone high-Z. All sorts of interesting symptoms can occur as a result. Exact-replacement caps are likely to be impossible to find - you may very well need to improvise, using a modern 'lytic of equal or greater capacity and WVDC rating, and some creative wiring and mounting arrangements to adapt the new cap(s) to the old pinouts. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
#6
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Rick & Joe,
Thanks for your suggestions, however, all of your mentioned items have been checked, and I am quite confident that the problem lies inside the box. I now have a 333 page service manual...that unfortunately is more oriented towards callibration than troubleshooting...but may lead to some useful information. Laurie |
#7
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I just finished repairing my 465 scope that had a similar problem. When powered up the trace would appear off
the left hand side of the screen. Turned out to be bad filter caps in the +5v and -8v supplies. Check the supply voltages at the TPs, if 2v or more less that what it should be then replace the caps. After looking at some of the Tek newsgroups I gather that bad filter caps are a common problem with Tektronix scopes. Richard WB8KRN "Laurie Landry" wrote in message ... My Tek 466 scope decided to misbehave. It will not display the horizontal beam unless I press the beam finder. When I do it displays whatever I'm looking at(eg: 7 Mhz sine wave) properly. I'm quite familiar with this scope, but possibly doing something stupid. Does anyone have any idea as to what the problem could be? Thanks in advance for any light you can shed on the problem. Laurie |
#8
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Richard,
I believe that you are on target. I will try to find the TPs and verify the voltages. You mention Tek newsgroups. Can you tell me their location. So far, they have eluded my searches. Thank you very much for your suggestion. Laurie |
#9
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Laurie,
Here is one group on yahoo, http://groups.yahoo.com/group/TekSco...guid=145910120 Another is the newsgroup, sci.electronics.repair, this group covers everything under the sun. I would tell you were to look but the 465 is different than the 466. Mine were on the "interface board" which is located on the bottom of the scope, they are pins with eyelets in the ends. Voltage should be marked on the pcb next to the test point pin. Richard WB8KRN "Laurie Landry" wrote in message ... Richard, I believe that you are on target. I will try to find the TPs and verify the voltages. You mention Tek newsgroups. Can you tell me their location. So far, they have eluded my searches. Thank you very much for your suggestion. Laurie |
#10
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Richard,
Thanks for the info on the groups. Regarding the voltages, they all check ok except the -8v is something like -7.78volts. Whether this is enough to cause the problem, is doubtful. Going through the service manual, there is more information than I thought at first glance. However, it calls for a lot of reading and my old eyes tire very rapidly! There was a 465 on ebay today, but I lost out. The 465 has a few less thing that can go wrong. But I suppose that digging into the 466 will help me learn a few things! Again, Richard, thanks for the advice. Laurie " |
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