Tektronix 453 Horizontal Display Compressed

[Feath3rblade]

I have a Tektronix 453 and lately the horizontal display has been acting up, compressing almost as if the trace finder is on, but the vertical works fine and although at first I though the trace finder was just stuck, pressing it compresses it even further so I doubt that that is what is up. I have been looking around nothing seems off at first glance, so I will have to dig deeper, but I am not sure on where exactly to start. I am assuming I will want to be looking at the horizontal amplifier, but I am not sure.

[particleman]

I would start with checking power supply voltages and ripple. Also get the manual if you don't have it.

[Feath3rblade]

I have started going through the calibration procedures in the manual and have found nothing wrong so far. I noticed that the trace is normal right after I turn the scope on though and only after a second does it compress towards the middle. I don't, however, have a second scope so I am unable to perform some of the tests.

[Feath3rblade]

UPDATE:
I have found that if I adjust the +75 volt supply to output 80 volts it works perfectly fine. Will this have other effects on the operation of the scope, or perhaps point to other issues within, or am I good to go?

[PaulAm]

Have you checked ALL of the power supplies?  If you don't have a second scope you can use a DMM to check for AC ripple on the outputs.  The specs are in the manual; the supply readings should meet them.  Check the -12V supply in particular.

You really don't want to set the 75 to more than 75.  If you need to change the gain of the H amp, there's a control for that.

You could have a problem in the H amp; it's pretty simple.  Have you reseated the transistors?  You might have a high resistance contact affecting the behavior.

[Feath3rblade]

I checked the ripple and on the +75 volt supply, got ~10.6 mV, on the +12 supply I got 0 mV, and most worryingly on the -12 volt supply I got ~245.2 mV of ripple. I have also noticed that some of the resistors and capacitors have drifted from their original values and I am assuming those will need to be replaced.

[PaulAm]

Try bridging C1112 with another capacitor, 500uF or more and see what happens to the ripple.  The filter caps are pretty robust, but they're around 50 years old now so they could be failing.  On the 453/454 scopes I don't replace them unless they're actually bad; they're a little hard to get to.

With these scopes you cannot look for any other problems until the power supplies are correct.

Wholesale component replacement without understanding how the part corresponds to the observed problem will likely lead to a junked scope.  This was not a piece of consumer gear or a service grade scope that used low cost parts, so if the observed problems are corrected and it passes calibration it will be fine.

[m3vuv]

ive got a 453,it seems to work fine except in xy mode,anyone know if its possible to get these into xy mode?,ive read the manual but its as clear as mud!.

[Andrewausfa]

Read the bit in the manual concerning 'External Horizontal', Ext Horiz on the Horizontal Display control. There is no specific XY switch or button.  It took me a while to get it too!

Andrew

[m3vuv]

ive tried that but nothing works!,just wondered if these 453 scopes can do xy?mode

[Feath3rblade]

I had issues as well and all I had to do was crank the intensity up a bit and it worked perfectly.

[Andrewausfa]

ive tried that but nothing works!,just wondered if these 453 scopes can do xy?mode

Yes, they definitely can. I did have one of those 'Aaaahhh..' moments when I sussed out what I needed to do.

Andrew

[PaulAm]

This really should have been a separate thread.

Look in the 453 manual on page 2-25 under X-Y Phase Measurements.  Use Ch1 and Ch2 as inputs, set the HORIZ DISPLAY switch to EXT HORIZ, set the TRIGGER switch to CH 1 ONLY and the B Triggering SOURCE switch to INT.

Now that was obvious, wasn't it?  On the 454 they put X/Y mode on the horizontal display switch, probably because nobody could figure it out on the 453.

[m3vuv]

thanks for that,why couldnt the manual been as clear as that?!!.73 m3vuv

[Feath3rblade]

I just grabbed a capacitor to jump C1112 and just want to know the easiest way to go about it. Right now I have removed the A trigger/ sweep board at the bottom but the diodes are in the way. Is there an easier way or will I have to jump it from here?

[pbarton]

I had a similar problem with a Tek 454A, the trace was only 60% the width of the screen in HORIZ DISP x1 mode and 95% the width of the screen in HORIZ DISP x10 mode.
Turned out to be a pair of resistors in Horr amp final output stage. Translating this back to your 453, I suggest that you verify that R364 and R374 are 650 ohms.
Replace if they are reading high. If they are high, you also need to verify that the fan is working.

[Feath3rblade]

The cap replacement has fixed the ripple and had made the issue much better, but the issue is still persisting. I did however, notice something interesting. I was fiddling with the scope and bumped the trace finder, which caused the screen to go back to normal. I pressed it again, and it was normal, but when I let it go, the issue was back. My trace finder is rather rusted, so does this point to an issue regarding it that would require a replacement or could I fix this with something as simple as bending the tabs?

EDIT, When pressed while the screen is compressed, the trace finder still compresses the vertical, but the horizontal is untouched.

[PaulAm]

It's rusted?  That could be your problem.  You might try to clean the contacts and see if that improves things.  I may be wrong,  it's been a while since I had one apart, but I think that was a leaf spring kind of switch and the contacts are accessible for cleaning.

[Feath3rblade]

Yup, that was the issue. Thanks for the help!