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Mdoc
Ehh... munch munch... what's up, Doc?
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1 edit
reply to neonhomer

Re: Tektronix 485 - no power up

said by neonhomer:

Thing is, it only did that when the U comb was removed.

Ah, so it was because the U comb was removed that you saw the flash. OK.

In the last schematic pic I posted, there's a blue dashed arrow. It's pointing at the resistor that connects to the x6 multiplier. Remove it and test for no clicks. (With the U comb in)


neonhomer
KK4BFN
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join:2004-01-27
Edgewater, FL
Okay.. will do and post results later....


neonhomer
KK4BFN
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Edgewater, FL
Just a brief update - Still haven't done anything else with the scope. Just haven't felt like dragging it out.


neonhomer
KK4BFN
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Edgewater, FL
Okay.... R1602.... problem is this resistor is on the transformer board. So I have to pull the xfmr board, remove this resistor, and then put the board back and then power up the unit.

Is there a way to do this w/o pulling the xfmr board?


drjim
Premium,MVM
join:2000-06-13
Long Beach, CA
kudos:3
How long are the leads on it? You could always clip one lead, lift it, and then solder back to the stub in the board.
--
One man's Magic is another man's Engineering.


neonhomer
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No. The resistor is located on the xfmr board, and it is under a cover. So it looks like pulling the xfmr board is the only way. Ugh...

I kinda wish I could have this thing to someone and have them fix it. Unfortunately, I don't have that kind of money...


Mdoc
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3 edits
reply to neonhomer
Click for full size
said by neonhomer:

Okay.... R1602.... problem is this resistor is on the transformer board. So I have to pull the xfmr board, remove this resistor, and then put the board back and then power up the unit.

Is there a way to do this w/o pulling the xfmr board?

Yes, you can do another way, but this will isolate what I don't want isolated: the circuitry for the CRT. You can just remove pin 3 of U comb and put the comb back in, and then test for no clicks. After this, re-insert pin 3.

Remove P1960 (diagram 15). The result should hopefully be that no clicks are heard. If still clicking, the problem is localized to before the P1960. We'll get to that if we get to this bridge.

Re-insert P1960 and do either one of these 2 approaches:
1) Remove everything in the circle (right side of pic above) from the A13 power board and test for no clicks. If no clicks, then re-attach each power line until you hear clicking. When that happens, you've narrowed down the culprit considerably, and that's where you should look much closely for problems. Or

2) Remove power lines singly and test as you go. The approach is similar to above, but inverted.

What you're looking for is a condition where there are no clicks. That's a condition where that part of the circuitry can be ruled out.

I hope the removal of P1960 demonstrates my thinking: that this stops the clicking. If it does not stop, either I'm barking up the wrong tree or my approach is wrong.


drjim
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join:2000-06-13
Long Beach, CA
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You guys keep mentioning "combs". Is that another term for one of the ribbon-type cables that has large pins crimped on the ends of it?
--
One man's Magic is another man's Engineering.


neonhomer
KK4BFN
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join:2004-01-27
Edgewater, FL
No. The combs almost remind me of a resistor pack. It's basically jumper pins in brick of five that interconnect the boards. When I get a chance to tear this thing apart again, I will take a picture of one of the combs...


drjim
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join:2000-06-13
Long Beach, CA
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I've probably seen them, but can't visualize what they look like.
Don't you have to be pretty careful bending the pins out of the way? I'd think they'd crack after a few bends!
--
One man's Magic is another man's Engineering.


neonhomer
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Yeah. I've only bent it out of the way once. So if I have to do it again, I am going to swap it with a different one So I don't stress the same one.


Mdoc
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1 edit
reply to drjim
said by drjim:

I've probably seen them, but can't visualize what they look like.

It's not one of these!


neonhomer
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Similar...... but only has 5 pins in it, and I don't believe they are electrically conductive to each other.

I am beginning to think the problem is with the transformer board, more to the point, the diode box thingy...

Well.... I can't find parts for this thing... so do I part it out, or just hold on to it and see if I can luck across another one for parts or the parts I need...
--
"F is for Fire that burns down the whole town...
U is for Uranium...... Bombs...
N is for NO SURVIVORS!!!!!" Sheldon Plankton


iknow

@optonline.net
said by neonhomer:

Similar...... but only has 5 pins in it, and I don't believe they are electrically conductive to each other.

I am beginning to think the problem is with the transformer board, more to the point, the diode box thingy...

Well.... I can't find parts for this thing... so do I part it out, or just hold on to it and see if I can luck across another one for parts or the parts I need...

is it one of these? »www.sphere.bc.ca/test/tek-parts/···ts5.html you don't need the exact one, just a compatible one. (same voltage and multiplication) even one from a T.V. that would have the same specs would work. or one could be made with HV diodes and caps..


Mdoc
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reply to neonhomer
said by neonhomer:

I am beginning to think the problem is with the transformer board, more to the point, the diode box thingy...

That's why I wanted you to isolate it by removing R1602 to confirm that. If you can find an easier way to break the line through R1602 to the multiplier, do that if you can.


neonhomer
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IIRC, the only way to break that connection is to remove the xfmr board again, and to unsolder it.

I just haven't had the motivation to tear the thing apart again to do it.

If I do isolate that line, what should happen?
--
"F is for Fire that burns down the whole town...
U is for Uranium...... Bombs...
N is for NO SURVIVORS!!!!!" Sheldon Plankton


Mdoc
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said by neonhomer:

If I do isolate that line, what should happen?

Theoretically, that it should stop clicking.
If it does, you've successfully isolated the problem.