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Tektronix 7633 Scope, Can anyone please help Old64goat!!!

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finom1:

--- Quote from: David Hess on May 02, 2017, 05:56:10 pm ---The available free scans of the 7633 service manual are actually pretty good and the one casinada linked is the one I have.

1. If the -1475 cathode voltage is missing, then check that Q1195 is good, capacitor C1198 is good, and that unregulated +15 volts is present across C1198; these are all shown in the upper left corner of schematic 7.  Fuse F814 located on the rectifier board and shown on the left side of schematic 8 supplies the unregulated +15 volts to the high voltage board but I think Old64goat checked it.

I know this means gaining access to the high voltage board but what are you going to do?  Unfortunately, I am not sure how to do that.  Someone else here are on the TekScopes@yahoogroups.com email list should know.

2. When you pull the reduced scan switch out on the front which I saw Old64goat messing with, then the -1475 cathode voltage is doubled to about -3000 volts while the PDA voltage stays the same.  This reduces the CRT deflection to 1/2 of its normal value and makes the display sharper and brighter.  This function makes the high voltage circuits more complicated on the 7633 than the 7623A which lacks this function.

3. Once the high voltage is working and if there is still no display, monitor the output of the z-axis amplifier to see if the beam is being unblanked and if the intensity control is working.  There is a procedure in the service manual for adjusting the transient response of the z-axis amplifier which describes how to monitor this signal.

4. That readout board we see in the video is one of the later analog/digital hybrid readout boards and produces the second best display in my opinion.  (1) The earlier boards used analog (!) ROMs and the hybrid board replaced them with a digital ROM so this 7633 is one of the later ones.  The service manual casinada linked only shows the earlier all analog readout board but that should not matter for this.  For those who are interested, the details of this hybrid analog/digital readout board can be found in the 7904A service manual.

(1) There is *another* hybrid analog/digital version which is even better (or at least as good) but this one is pretty good.  My favorite 2232 use a similar character generation method and looks great.  Vector is always better than raster.

--- End quote ---

Hi David,
Old64goat is going to make another video to provide more information after reading your post, that you so kindly provided!!!

Thank you for trying to help him, he is a very nice person just trying to get his vintage electronics repair shop up and running again!!!

Thanks again!!!

dave_k:
In his first video, he says the pilot light for the main power light is not working. This might indicate a short to ground on the 5v supply rail. I had a similar fault in a 7603 scope, which was traced to a shorted cap on the main interface PCB.

james_s:
Does this use a voltage multiplier to generate the high voltage? I've seen shorted capacitors in those cause a lack of HV while not greatly affecting lower voltages coming off the same transformer.

finom1:
David,
Here is the video he made for you:
Video For The EEVblog Forum -

Thank you David for all your help!!!

Everyone please leave feedback on his video also, so he can respond to you faster!!!

finom1:

--- Quote from: dave_k on May 02, 2017, 07:36:20 pm ---In his first video, he says the pilot light for the main power light is not working. This might indicate a short to ground on the 5v supply rail. I had a similar fault in a 7603 scope, which was traced to a shorted cap on the main interface PCB.

--- End quote ---

Thank you for helping him. Please see his latest video!!!

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