Tektronix 468 horizontal problem in storage mode

turboroe · 8th October 2010, 07:07 AM

Hi there!
I´m having some trouble with my Tektronix 468 and I would be very gratefull if you could give me some advice.

In real mode it works perfectly (even the uncal knob and light), but in storage mode it goes crazy.
Here are the symptoms in storage mode:

-The time/div is not correct (it is about 20 times what it should be, so the signal looks 20 times wider)
-The wave displayed is distorted (square wave looks like a rounded trapezoid)
-The display jumps sideways a bit.
-The uncal lamp, when on, is very dark
-The uncal knob when turned on does nothing
-There is a vertical line at the end of the beam with 2 dots on the edges (see pic)

On both input channels the results are the same, and the vertical circuits and trigger circuits are both working fine, so I guess it is something on the top board, the storage part?
Do you have any idea of what this could be?

Pictures taken:

macboy · 18th October 2010, 02:15 PM

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indianajo · 12:25 AM

Bought a Tek 468 25 years ago at work - thank you Generous Elec. Yours has to be nearly as old and expensive electrolytic capacitors last - - - 20 years. My favorite rant, you should stop thinking, look at the part list, and buy one of everything electrolytic. Discharge caps with resistor , measure below 25 VDC before touching - lethal voltages in there. Change two caps at a time and then test, since you might mess up or the new ones might be unsuitable in some way. If doesn't work as least as well as before the latest caps went in- back up with the old ones and think a bit about the circuit.
If you want it to stay fixed, use caps that are rated 2000 hours or more by the manufacturer. Newark.com or farnell.co.uk have the hours shown in their selector tables for caps. Don't buy sale caps, they are going out of date already.
Left that job 15 years ago, now making do with a 20 MHz B&K non- memory scope. Oh, well, back to reality as the song goes.

8th October 2010, 07:07 AM	#1
turboroe diyAudio Member Join Date: Oct 2009	Tektronix 468 horizontal problem in storage mode Hi there! I´m having some trouble with my Tektronix 468 and I would be very gratefull if you could give me some advice. In real mode it works perfectly (even the uncal knob and light), but in storage mode it goes crazy. Here are the symptoms in storage mode: -The time/div is not correct (it is about 20 times what it should be, so the signal looks 20 times wider) -The wave displayed is distorted (square wave looks like a rounded trapezoid) -The display jumps sideways a bit. -The uncal lamp, when on, is very dark -The uncal knob when turned on does nothing -There is a vertical line at the end of the beam with 2 dots on the edges (see pic) On both input channels the results are the same, and the vertical circuits and trigger circuits are both working fine, so I guess it is something on the top board, the storage part? Do you have any idea of what this could be? Pictures taken:

18th October 2010, 11:59 PM	#3
indianajo diyAudio Member Join Date: Jan 2010 Location: Jeffersonville, Indiana USA	aging 468 Bought a Tek 468 25 years ago at work - thank you Generous Elec. Yours has to be nearly as old and expensive electrolytic capacitors last - - - 20 years. My favorite rant, you should stop thinking, look at the part list, and buy one of everything electrolytic. Discharge caps with resistor , measure below 25 VDC before touching - lethal voltages in there. Change two caps at a time and then test, since you might mess up or the new ones might be unsuitable in some way. If doesn't work as least as well as before the latest caps went in- back up with the old ones and think a bit about the circuit. If you want it to stay fixed, use caps that are rated 2000 hours or more by the manufacturer. Newark.com or farnell.co.uk have the hours shown in their selector tables for caps. Don't buy sale caps, they are going out of date already. Left that job 15 years ago, now making do with a 20 MHz B&K non- memory scope. Oh, well, back to reality as the song goes. __________________ Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,SP2-XT's, T-300 HF Projs, Steinway console, Herald RA88a mixer, Wurlitzer 4500 Last edited by indianajo; 19th October 2010 at 12:25 AM.

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18th October 2010, 02:15 PM	#2
macboy diyAudio Member Join Date: Oct 2003 Location: Ottawa, Canada	If you don't already have them, you can download the service manuals from Welcome to EBAMAN (free, but need to register)

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