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Scope on the bench ready for refurb.
Scope on the bench ready for refurb.
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Old 13th February 2018, 01:32 AM   #11
audio king is offline audio king  Canada
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Yep,Tek's are definitely made for the long haul.I got my 547 around 1991,and since then I've replaced two tubes.I've slowed down a lot,but she used to run all day,every day.Former line scope for an aerospace manufacturer.
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Old 21st July 2018, 06:50 PM   #12
mashaffer is offline mashaffer  United States
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I finally got around to replacing those broken tubes. The dim bulb wasn't allowing enough voltage through for it to start it up so I took the chance and plugged it in directly.

I turned it on and got a faint vertical line part way up the crt but after a minute or less I heard a snap that could have been arcing or a relay so I shut it off and removed the right side panel and turned it back on. I got a bit of a scare. When I heard the snap this little guy suddenly glowed bright orange!

20180721_141650-1.jpg

So I switched it off and lookup the tube at Frank's. Turns out it is a gas VR tube so I gather the scary glow is proper. :D
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Old 21st July 2018, 09:41 PM   #13
mashaffer is offline mashaffer  United States
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When I let it finish coming up I get a bright horizontal line approx. 1/4 of the width which slowly traverses from bottom to top disappearing off the top apparently forever. So the CRT seems to be working. I have no probes or even a BNC cable so I am not sure I can do much more until I have a way to present an input but I will entertain any suggestions.

Capture+_2018-07-21-17-11-10.jpg
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Old 22nd July 2018, 04:45 AM   #14
PRR is online now PRR  United States
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> I have no probes or even a BNC cable so I am not sure I can do much more until I have a way to present an input

Stick one end of a 1K 1/2W resistor in the middle of the BNC. Not a great connection, but it will not damage the BNC. Put your finger on that, you can read room-hum (after you work out sweep and triggering). Get red and green clip-leads, you can do about anything audio. (Hook the resistor with a rubber-band to keep contact in the BNC.)
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Old 22nd July 2018, 08:40 PM   #15
mashaffer is offline mashaffer  United States
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One good thing is that pretty complete documentation is available. On my phone I have a pdf of the manuals for the "A" model and "B"models (mine is B) and the CA input plugin modual that include calibration, troubleshooting, and schematics information.

At this point I get a brief spot when the relay kicks in before it flys off screen. There is a little smudgy "tail" that corrisponds to the horizontal position of the beam. If I turn the horizontal possition all the way to the right the tail appears on the left side of the screen.

So we have excess deflection in both axes. I imagine the first step should be to check the voltages in the "low" voltage supply. I don't have a KV meter to check the high voltage supply. If that checks out I suppose the horizontal amplifier is the next thing to check.

Here you can see the tail.

Capture+_2018-07-22-16-30-46.jpg

I wonder if it is possible to run with the plugin removed to see if the vertical problem is in it or the builtin vertical amplifier.
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Old 23rd July 2018, 02:46 PM   #16
mashaffer is offline mashaffer  United States
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As Mama taught me I must fess up to the stupid. Going to check the LV supply I switched my meter probe from alligator clip to small tip so I could get into the ceramic strips. Unfortunately I plugged it into the 10A socket rather than the V+. As you can imagine I woke up when I tried to measure the first voltage. Putting the probe in the right socket (and testing that the meter still functions) I can measure no Voltage at any LV test points.

I thought that I might have blown a fuse but according to the manual there is only one fuse (for either 120 or 220V) and the tubes still light, crt still lights up, fan and relay all operate so certainly I have not blown the main fuse. I thought to check anyway but after loosening the screws the fuse cover won't come off. Must be some trick to it.

I guess I need to troubleshoot the LV supply but apparently that is one schematic that is not in the manual.
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Old 23rd July 2018, 03:28 PM   #17
mashaffer is offline mashaffer  United States
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I should never do important stuff in the morning. :{

-150=-197
100=137
225=299
350=464
500=610
75=104
325 unregulated=337

So all voltages very high.

Note to self AC and DC much different animals.

P.S. correction.ps is in manual. Hard to see on phone.
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Last edited by mashaffer; 23rd July 2018 at 03:34 PM.
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Old 23rd July 2018, 04:03 PM   #18
1audio is offline 1audio  United States
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Scope on the bench ready for refurb.
A quick guess here- The HV is OK or the traces would spread across the screen(Lower HV give the deflection more control). I believe they are all regulated and refer to one as a master. The manual will walk you through the supply checking and adjustment. Going high would suggest either a resistor changing value or some load pulling too much and everything overreacting. Possibly a supply cap failing. Check the supplies with the plugin removed.

I found a manual online (also "old school" in the DJVU format, something I have not seen in years). The sole adjustment is for the -150V supply. Everything else references that. So step 1 is to adjust it. The snap you heard was the delayed power on for the supplies. One of the reasons these last so long is that the supplies don't start until the filaments are fully warmed up. The supply is as complex as a solid state supply except for only NPN equivalent devices. Everything regulated. You should see why it's so far out of regulation. There are probably some other issues hiding in there.

I have had a number of the tube scopes. The cost of the power to run them became prohibitive here in California. Usually, once they are running you can ignore them for years.
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Old 23rd July 2018, 08:26 PM   #19
mashaffer is offline mashaffer  United States
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Thanks. I appreciate the help.

For our reference...
Attached Images
File Type: jpg Tek_545b_power_supply.jpg (564.6 KB, 152 views)
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Old 24th July 2018, 03:42 AM   #20
1audio is offline 1audio  United States
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Scope on the bench ready for refurb.
Two good references for Tek: TekScopes@groups.io | Home and 545 - TekWiki
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