tektronix 468 with dm44

[vinhdinh]

Hello, I have recently acquired a tektronix 468 with a dm44. When I got it, it was not in working condition. There are three main problems and I have a few questions and to verify some of my thoughts about them.

1.) Channel 1 does not work. Nothing shows up for channel 1. I haven't looked too much into it because channel 2 kind of works. I think looking at the schematic for chan 1 would be a good start.

2.) A dot appears in channel 2. I can move it vertically and horizontally which seems pretty good. When i turn on the unit the "READY" light comes on, and once I turn the volt/div, a very fast wave appears on the screen then the dot comes back on. The TRIG light then comes on and nothing happens after that until I turn off the unit and start it back up. I checked all the voltages 55v, 5v, 110v, etc and they all appear to be correct. I haven't checked the filter caps as recommended by a lot of people but I don't exactly know how to do that. Could it be something else? Maybe the sweep amplifier or something.

3.) The dm44 does not work. I checked for 5v and 12v on the board and it appears that nothing is happening there. I think if I can find the power source for it and see if there is a broken connection or something. Can someone suggest something I should try as well?

In the meantime I've been looking at the manual which seems to be rather long and confusing. If someone can think of other ideas or point me in the right direction I could get this thing up and running. Thanks in advance.

 

[shrtrnd]

This may not help, but consider it.
The FIRST thing I do, is check the actual on/off operation of the front panel push-buttons on the front panel. When one fails or sticks, it holds-out functions you're expecting to see on the scope. Clean the switches, and especially the rotary wafer switches you probably have on a scope that old. You're not going to get anywhere, if the selector switches you're using, are not working right. Good Luck.
(Contact cleaner spray can)

 

[vinhdinh]

This may not help, but consider it.
The FIRST thing I do, is check the actual on/off operation of the front panel push-buttons on the front panel. When one fails or sticks, it holds-out functions you're expecting to see on the scope. Clean the switches, and especially the rotary wafer switches you probably have on a scope that old. You're not going to get anywhere, if the selector switches you're using, are not working right. Good Luck.
(Contact cleaner spray can)

Thanks for the reply. I spent this morning cleaning all the contact points, there are a LOT and so many hard to reach places I had to take some of the boards out. I also cleaned it with some air as well. I tested with a multimeter the buttons on the left side which turn on and off ch1 and 2. It appears as though ch2 does not do anything when I press it, the dot just stays on.

 

[shrtrnd]

That may explain why you can't select channel one.
If channel two is selected continuously, you CAN'T select channel one.
(Your channel two push-button switch is bad)
You'll have to replace the switch, then, having cleaned the switches, see what you've got.

 

[vinhdinh]

That may explain why you can't select channel one.
If channel two is selected continuously, you CAN'T select channel one.
(Your channel two push-button switch is bad)
You'll have to replace the switch, then, having cleaned the switches, see what you've got.

I was under the impression that I can have both ch1 and ch2 on at the same time, so would it matter if the ch2 is selected continuously?