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Tek 577 Cruve Tracer, no trace/dot, find beam works but unable to adjust.

twincam18@...
 

Hello, this is my first post here. I hope I am placing this in the right spot.

I have a 577 Curve Tracer that I bought from school surplus. It had been sitting in storage for many years. Upon power-up, I do not get a trace/dot on the screen. However, if I press the 'beam finder' button it shows a dot in the lower middle of the screen. Yet when I go to adjust the beam onto the screen neither the horz or vert position knobs make any change. If I hold down the find beam button and turn any of the scope settings there is no change on the beam dot, it stays in the same place and a single small dot.

I have checked the voltages that come into to the deflection amplifier/high voltage board. There is a 200v+, 30v-, 30v+. 5v+ and they are all right on the dot. I have done a quick visual inspection and esr readings on most the capacitors and so far I am not seeing anything.

Any help or just ideas of what I should check would be greatly appreciated!

Mlynch001
 

The 577 has something called “auto-position”, This circuit routes through the test fixture, possible something is amiss there? I have not worked on a 577, but that is where I would start.

--
Michael Lynch
Dardanelle, AR

Mlynch001
 

Or possibly the deflection amplifier? see Sheet 6 and Sheet 7 of the schematic. Should be easy enough to verify voltages and/or waveforms through the circuit. Look for a common point that would affect both Horizontal and Vertical alike.
--
Michael Lynch
Dardanelle, AR

Abc Xyz
 

Mike,

I am currently troubleshooting Trace problems on my 465B Tektronix
Ocilloscope.

JR

On Thu, Aug 1, 2019, 2:07 PM Mlynch001 <@mlynch001> wrote:


Or possibly the deflection amplifier? see Sheet 6 and Sheet 7 of the
schematic. Should be easy enough to verify voltages and/or waveforms
through the circuit. Look for a common point that would affect both
Horizontal and Vertical alike.
--
Michael Lynch
Dardanelle, AR



Mlynch001
 

On Thu, Aug 1, 2019 at 11:48 AM, <twincam18@...> wrote:


Hello, this is my first post here. I hope I am placing this in the right spot.


I have a 577 Curve Tracer that I bought from school surplus. It had been
sitting in storage for many years. Upon power-up, I do not get a trace/dot on
the screen. However, if I press the 'beam finder' button it shows a dot in the
lower middle of the screen. Yet when I go to adjust the beam onto the screen
neither the horz or vert position knobs make any change. If I hold down the
find beam button and turn any of the scope settings there is no change on the
beam dot, it stays in the same place and a single small dot.

I have checked the voltages that come into to the deflection amplifier/high
voltage board. There is a 200v+, 30v-, 30v+. 5v+ and they are all right on the
dot. I have done a quick visual inspection and esr readings on most the
capacitors and so far I am not seeing anything.

Any help or just ideas of what I should check would be greatly appreciated!
I forgot to ask, how are the controls set up? You should have them set per the Operation Manual under “Preliminary settings”.

--
Michael Lynch
Dardanelle, AR

DW
 

Perhaps you might check the socketed chips on the board located on the right side of the instrument. Carefully wiggle or reinsert the IC's in their sockets, the transistors are also removable as well so give them a careful moving around, maybe this might improve things if there is oxidation on the contacts. I recently had to replace a failing IC that was on the CRT horizontal driver. Also on this forum it was mentioned these 577's can have IC sockets that are prone to failing due to their design.

Here is some more information on the the horizontal and vertical display CRT driver IC's
U520 U530 Horizontal driver MC1456N 8 PIN DIP
U570 Vertical driver MC1456N 8 PIN DIP

Here is a quick test I did on a 577 you could perform
With the horizontal and vertical display controls centered, collector supply set to 6.5V, collector supply polarity set to AC, horizontal volts division set to 0.5V, if you adjust the variable collector supply with the beam finder button pushed do you notice the appearance of a emerging horizontal line on the screen? If so then I believe your horizontal circuit is somewhat working.

 

On Thu, Aug 1, 2019 at 06:48 PM, <twincam18@...> wrote:


I have checked the voltages that come into to the deflection amplifier/high
voltage board. There is a 200v+, 30v-, 30v+. 5v+ and they are all right on the
dot. I have done a quick visual inspection and esr readings on most the
capacitors and so far I am not seeing anything.

Any help or just ideas of what I should check would be greatly appreciated!
Unlike the 576 Test Fixtue the 577 Test Fixture (177) is not passive i.e it has a
pre amp. If the input FET get busted it will send the beam off screen. I've seen
this happen several times.

If my memory is correct this could happen due to arcing in the Looping Compensation
variable cap when the Collector Supply is set to its max (> 1600V) and the Vertical Current/div
is set to a low current.

So checking the output from the 177 would be a good place to start.

/Håkan