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My 485 has a sweep issue of some kind. The sweep will only occupy 8 of the 10 divisions on the screen for some reason. When is set th time bse for 1or 5 or 10 us the sweep gets even shorter. Any one seen this kind of response before? Wonder where I should start look for the problem at??
Steve
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Steve,
I have a Similar Problem on my 465B. I'm told its something in the
Horizontal Section but I can't seem to Find the Culprit. One Member here
found a Bad Capacitor in the Horizontal Section on his Scope that had a
Short Trace. I also Read that Tektronix had Issues with the Horizontal
Section on these Scopes. How True that may be I do not know.
Shorting various Stages in the Horizontal Section apparently can Narrow
down where the Fault lies. Anyway, there are some Really Experienced and
Generous People on this Site so you are off to a Good Start.
JR
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On Fri, Nov 8, 2019, 4:04 AM stephen white <sswhite@...> wrote: My 485 has a sweep issue of some kind. The sweep will only occupy 8 of
the 10 divisions on the screen for some reason. When is set th time bse
for 1or 5 or 10 us the sweep gets even shorter. Any one seen this kind of
response before? Wonder where I should start look for the problem at??
Steve
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So far I have managed to save this unit from the dumpster, I hate to see items like this end up in the landfill...It had a broken shaft coupling on the vertical adjustment pot and I could not find a proper replacement so I had to rebuild/repair that... So what you have said is at least a hint, I was not sure if it was a sweep issue so will look harder at the horizontal section to see if I can find a problem.
Thanks and if anyone else wants to put there oar in the water i would appreciate it...
steve
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Steve,
I will be watching to see what you find out and how you found it... your
experience may help me in finding the Fault in my 465B.
JR
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On Fri, Nov 8, 2019, 6:43 AM stephen white <sswhite@...> wrote: So far I have managed to save this unit from the dumpster, I hate to see
items like this end up in the landfill...It had a broken shaft coupling on
the vertical adjustment pot and I could not find a proper replacement so I
had to rebuild/repair that... So what you have said is at least a hint, I
was not sure if it was a sweep issue so will look harder at the horizontal
section to see if I can find a problem.
Thanks and if anyone else wants to put there oar in the water i would
appreciate it...
steve
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I had sweep length and linearity problems in my 485, which I traced to
U960. You may want to check the +13V rail on the timing board.
I had a couple of bad 741s on mine, plus R961 was wonky - it measured good,
but had voltage or self-heating related drift.
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On Fri, Nov 8, 2019 at 7:04 AM stephen white <sswhite@...> wrote: My 485 has a sweep issue of some kind. The sweep will only occupy 8 of
the 10 divisions on the screen for some reason. When is set th time bse
for 1or 5 or 10 us the sweep gets even shorter. Any one seen this kind of
response before? Wonder where I should start look for the problem at??
Steve
|
On 08/11/19 16:44, Siggi wrote: I had sweep length and linearity problems in my 485, which I traced to
U960. You may want to check the +13V rail on the timing board. Replace all the (ISTR 3) 15V tants on that line, before they toast the resistor next to C911.
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Hello JR,
In my 465b, this short sweep/trace problem was due to a faulty potentiometer, x1 gain in the horizontal amplifier section. Replacing this pot and adjusting 1x gain fixed this problem for me. It was a Bourns 3352 series pot, which had lost contact from the slider with the track.
Later I found many other faults in my scope, which were all due to failed or about to fail Bourns 3352 pots in various sections. They all had similar failure, probably due to ageing. I ended up doing a full replacement of all Bourns 3352 pots in the scope and then calibration of circuits where the pots had failed.
Hope this is of some help.
Shailendra
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On Fri, Nov 8, 2019 at 06:13 PM, <skv1958@...> wrote:
Later I found many other faults in my scope, which were all due to failed or
about to fail Bourns 3352 pots in various sections. They all had similar
failure, probably due to ageing. I ended up doing a full replacement of all
Bourns 3352 pots in the scope and then calibration of circuits where the pots
had failed.
ISTR that the 3352 was introduced as a low-cost cermet trimpot. In recent years, I have found many samples where the plastic mushroom-shaped stem lost its flattened head so contact pressure against the conductive trace was lost. Raymond
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Shailendra, How did you go about Finding that Faulty Potentiometer? JR On Fri, Nov 8, 2019, 9:13 AM skv1958 via Groups.Io <skv1958= [email protected]> wrote: Hello JR,
In my 465b, this short sweep/trace problem was due to a faulty
potentiometer, x1 gain in the horizontal amplifier section. Replacing this
pot and adjusting 1x gain fixed this problem for me. It was a Bourns 3352
series pot, which had lost contact from the slider with the track.
Later I found many other faults in my scope, which were all due to failed
or about to fail Bourns 3352 pots in various sections. They all had similar
failure, probably due to ageing. I ended up doing a full replacement of all
Bourns 3352 pots in the scope and then calibration of circuits where the
pots had failed.
Hope this is of some help.
Shailendra
|
On Fri, Nov 8, 2019 at 06:32 PM, Abc Xyz wrote:
Shailendra,
How did you go about Finding that Faulty Potentiometer?
I found them because they turn very easily or have bad/scratchy behaviour. Raymond
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Hi Gang:
Whenever I have a 485, or any other scope for that matter, in my shop for refurbishing I always tap on every potentiometer with a screwdriver handle end while watching the CRT.? If I see any flickering I replace that pot.
As to the shortened trace I would strongly suspect the X6 voltage multiplier, U1600.? The failure pattern for U1600 is a short trace in the center of the CRT.? Sometimes the trace is not visible for several seconds after applying power? To determine if U1600 is putting out 21KV proceed as follows:
1) Disconnect all inputs to the neck of the CRT.? This opens a return path for a high voltage arc which will happen next if U1600 is good.2) Apply power and wait about a minute.3) Remove power and immediately pull out the high voltage connector at the left rear of the scope.? Move the removed end near the CRT metal shield and if you get a big spark you know U1600 is OK.? If you leave the 6 neck connections on the CRT when doing this test you will have an excellent chance of killing U660, the vertical amplifier output.? This fact was verified by me the herd way, I lost two U660's
If no spark occurs you know the X6 multiplier is bad and must be replaced.? They are available as a new item from Voltage Multiplier Inc., Visalia, CA as item VM176.? Price a year ago was $150 each.? If you replace U1600 carefully check R1602, a 15K, 1/2W resistor.? It is frequently toasted if U1600 is bad.
The 485, in my opinion, is the best analog scope Tektronx ever made.? It is versatile, robust, small, has excellent bandpass,? reliabile, fairly easy to repair and has many features that are outstanding.
Good luck but, whatever you do, do not trash it.
Reed Dickinsonreed714@...
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On Friday, November 8, 2019, 09:42:50 AM PST, Raymond Domp Frank <hewpatek@...> wrote: On Fri, Nov? 8, 2019 at 06:32 PM, Abc Xyz wrote:
Shailendra,
How did you go about Finding that Faulty Potentiometer?
I found them because they turn very easily or have bad/scratchy behaviour. Raymond
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JR,
I tried just adjusting x1 gain pot, assuming that it may have drifted over time ( I received the scope in that condition ). When I turned the pot, nothing happened to trace length. I measured the resistance and found it open circuit.
On other such pots, I could see that pressing vertically on the adjustment knob changed the settings of that parameter. That gave me the clue.
In other words, I did a "Re Pot" on my scope, on the lines of a "Re Cap".
Shailendra
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Reed,
Thanks for the Tapping Trick on Potentiometers! Any Tips on a 465B with
Short Traces?
JR
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On Fri, Nov 8, 2019, 5:17 PM Reed Dickinson <reed714@...> wrote: Hi Gang:
Whenever I have a 485, or any other scope for that matter, in my shop for
refurbishing I always tap on every potentiometer with a screwdriver handle
end while watching the CRT. If I see any flickering I replace that pot.
As to the shortened trace I would strongly suspect the X6 voltage
multiplier, U1600. The failure pattern for U1600 is a short trace in the
center of the CRT. Sometimes the trace is not visible for several seconds
after applying power To determine if U1600 is putting out 21KV proceed as
follows:
1) Disconnect all inputs to the neck of the CRT. This opens a return path
for a high voltage arc which will happen next if U1600 is good.2) Apply
power and wait about a minute.3) Remove power and immediately pull out the
high voltage connector at the left rear of the scope. Move the removed end
near the CRT metal shield and if you get a big spark you know U1600 is OK.
If you leave the 6 neck connections on the CRT when doing this test you
will have an excellent chance of killing U660, the vertical amplifier
output. This fact was verified by me the herd way, I lost two U660's
If no spark occurs you know the X6 multiplier is bad and must be
replaced. They are available as a new item from Voltage Multiplier Inc.,
Visalia, CA as item VM176. Price a year ago was $150 each. If you replace
U1600 carefully check R1602, a 15K, 1/2W resistor. It is frequently
toasted if U1600 is bad.
The 485, in my opinion, is the best analog scope Tektronx ever made. It
is versatile, robust, small, has excellent bandpass, reliabile, fairly
easy to repair and has many features that are outstanding.
Good luck but, whatever you do, do not trash it.
Reed Dickinsonreed714@...
On Friday, November 8, 2019, 09:42:50 AM PST, Raymond Domp Frank <
hewpatek@...> wrote:
On Fri, Nov 8, 2019 at 06:32 PM, Abc Xyz wrote:
Shailendra,
How did you go about Finding that Faulty Potentiometer?
I found them because they turn very easily or have bad/scratchy behaviour.
Raymond
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Hi Jr:
Same procedure as the 485.? Tap on every variable component including pots, varcaps, switches and connectors.
The 465B uses a voltage doubler so you can check it the same way.? Just make sure you do not leave a return path for current from the CRT into the solid state drive components.
Reed
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On Friday, November 8, 2019, 05:53:18 PM PST, Abc Xyz <yawrdanza@...> wrote: Reed, Thanks for the Tapping Trick on Potentiometers! Any Tips on a 465B with Short Traces? JR On Fri, Nov 8, 2019, 5:17 PM Reed Dickinson <reed714@...> wrote: ? Hi Gang:
Whenever I have a 485, or any other scope for that matter, in my shop for
refurbishing I always tap on every potentiometer with a screwdriver handle
end while watching the CRT.? If I see any flickering I replace that pot.
As to the shortened trace I would strongly suspect the X6 voltage
multiplier, U1600.? The failure pattern for U1600 is a short trace in the
center of the CRT.? Sometimes the trace is not visible for several seconds
after applying power? To determine if U1600 is putting out 21KV proceed as
follows:
1) Disconnect all inputs to the neck of the CRT.? This opens a return path
for a high voltage arc which will happen next if U1600 is good.2) Apply
power and wait about a minute.3) Remove power and immediately pull out the
high voltage connector at the left rear of the scope.? Move the removed end
near the CRT metal shield and if you get a big spark you know U1600 is OK.
If you leave the 6 neck connections on the CRT when doing this test you
will have an excellent chance of killing U660, the vertical amplifier
output.? This fact was verified by me the herd way, I lost two U660's
If no spark occurs you know the X6 multiplier is bad and must be
replaced.? They are available as a new item from Voltage Multiplier Inc.,
Visalia, CA as item VM176.? Price a year ago was $150 each.? If you replace
U1600 carefully check R1602, a 15K, 1/2W resistor.? It is frequently
toasted if U1600 is bad.
The 485, in my opinion, is the best analog scope Tektronx ever made.? It
is versatile, robust, small, has excellent bandpass,? reliabile, fairly
easy to repair and has many features that are outstanding.
Good luck but, whatever you do, do not trash it.
Reed Dickinsonreed714@...
? ? On Friday, November 8, 2019, 09:42:50 AM PST, Raymond Domp Frank <
hewpatek@...> wrote:
? On Fri, Nov? 8, 2019 at 06:32 PM, Abc Xyz wrote:
Shailendra,
How did you go about Finding that Faulty Potentiometer?
I found them because they turn very easily or have bad/scratchy behaviour.
Raymond
|
Lots of good ideas but I cant get back to this problem for 10 days or so..So your suggestions have to wait I guess...steve
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I suggest that the HV Multiplier is bad. I had a 468 and a 475 that both had bad HV Multipliers (Both shorted). On my units with a shorted HV Multiplier. there was no trace until the service jumper was removed. The shorted multiplier was grounding the HV transformer and loading it to the point that no trace was produced, my -2450V was only about -300V. If the HV Multiplier has failed ¡°open¡± instead of ¡°shorted¡±, then the trace will be shorter than normal, regardless of the service jumper. An open HV multiplier will not load the HV transformer but the post deflection acceleration voltage will still not be there. On my particular units, Once the service jumper was removed, the short to ground was removed, my -2450V was restored and my trace came back, but in a shortened version, in either scenario there was no post deflection acceleration voltage. Replacing the HV Multiplier restored both units to a full trace. My 2 cents. I would love to hear any other ideas on this fault.
--
Michael Lynch
Dardanelle, AR
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I had a similar issue with my 465. It turned out to be a 2uf capacitor on the 90 volt supply was leaky.
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Dave,
How did you Find the Leaky Capacitor?
JR
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On Sat, Nov 9, 2019, 2:26 PM DaveH52 <ac2gl.dave@...> wrote: I had a similar issue with my 465. It turned out to be a 2uf capacitor on
the 90 volt supply was leaky.
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On Sat, Nov 9, 2019 at 04:25 PM, DaveH52 wrote:
I had a similar issue with my 465. It turned out to be a 2uf capacitor on the
90 volt supply was leaky.
90V supply in a 465/465B or 475? Unreg +120/110,+110,-8,+5 +15 and +55 are the only ones that I have ever seen. Have I missed something? -- Michael Lynch Dardanelle, AR
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Michael,
I was thinking the same thing.
JR
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On Sat, Nov 9, 2019, 3:54 PM Mlynch001 <mlynch002@...> wrote: On Sat, Nov 9, 2019 at 04:25 PM, DaveH52 wrote:
I had a similar issue with my 465. It turned out to be a 2uf capacitor
on the
90 volt supply was leaky.
90V supply in a 465/465B or 475? Unreg +120/110,+110,-8,+5 +15 and +55
are the only ones that I have ever seen. Have I missed something?
--
Michael Lynch
Dardanelle, AR
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Raymond Domp Frank
Mlynch001
DaveH52