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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

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Old 6th Oct 2019, 3:50 pm   #21
M3VUV51
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Default Re: Tek 453A-1 no trace.

heres some pics of both running the same tb on the same cal signal
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Old 6th Oct 2019, 3:58 pm   #22
RogerEvans
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Default Re: Tek 453A-1 no trace.

Is the factor of 1.5 error in the X deflection matched by the same factor of 1.5 in the Y deflection?

The manual shows voltages around the HV regulator circuitry of Q913, Q914 and Q923, you could check these with a DMM.

I can't find VR911 or R926 in either of my 453A manuals including the KO4BB one that you were referred to on TekScopes. R925 dissipates around 220mW if working as per the manual and is rated at 0.5W so it should be quite warm. It does have 75V on one end.

Roger

OK the deflection errors in X and Y are different, crossed with you posting the pictures. So there is something affecting the X calibration

Last edited by RogerEvans; 6th Oct 2019 at 4:02 pm. Reason: Crossed with posting of pictures
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Old 6th Oct 2019, 4:02 pm   #23
M3VUV51
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Default Re: Tek 453A-1 no trace.

hi roger yes its seems off by the same amount in both x +y axis,the hv pot still does nothing as well.
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Old 6th Oct 2019, 4:02 pm   #24
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Default Re: Tek 453A-1 no trace.

You'll have to take a structured approach to this otherwise you'll waste a lot of time.



1. LV supplies need to be correct; the +75V rail is used as a reference for the EHT.

2. If the EHT is set wrongly, the horizontal and vertical time/div etc will be wrong: EHT too low = more deflection of the beam.



Does the time/div error persist on other setting of the time-base? (you need to get onto another "decade" to change the timing resistor).


John
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Old 6th Oct 2019, 4:03 pm   #25
M3VUV51
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Default Re: Tek 453A-1 no trace.

yes john it seems to be off on all tb settings.
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Old 6th Oct 2019, 4:06 pm   #26
RogerEvans
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Default Re: Tek 453A-1 no trace.

In picture 2 and 3 the Ch2 variable knob is not lined up in the cal position.

Roger
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Old 6th Oct 2019, 8:02 pm   #27
M3VUV51
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Default Re: Tek 453A-1 no trace.

Yes but they were both clicked to off,just remembered ,last night i had pulled one leg of 3 .1 caps in the hv section,then the tb looked ok,i put them back in circuit ,maybe gonna pull them againe and look,noticed also last night the grid bias pot made a differenc when altered,i gues one of the caps is leaky bringing the hv to its knees? ,its a job for tomorow.
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Old 7th Oct 2019, 5:32 pm   #28
M3VUV51
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Default Re: Tek 453A-1 no trace.

well im making sort of progress,when i got the scope q1034 on the z axis board was dead,,i replaced it and it brought up a trace,but something killed the replacement,ive replaced that too but its running well hot and still the r900 hv pot does nothing!,i pulled q1024 and q1034 still ran hot,then pulled q 1043,it then ran cool,so with either q 1024 or q 1043 in place q 1034 gets too hot,still the hv pot does nothing,any ideas where to look?,cheers Paul m3vuv.
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Old 8th Oct 2019, 9:35 am   #29
RogerEvans
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Default Re: Tek 453A-1 no trace.

You could try measuring the voltages on the Z axis board as shown in blue on the schematic.

Roger
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Old 8th Oct 2019, 5:51 pm   #30
John_BS
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Default Re: Tek 453A-1 no trace.

Quote:
You could try measuring the voltages on the Z axis board as shown in blue on the schematic.

Yes, and check the +90V rail is about right. Also put the mains voltage selector to High if it's not already there.

John


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Old 9th Oct 2019, 3:33 pm   #31
M3VUV51
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Default Re: Tek 453A-1 no trace.

well,it looks like its finaly fixed it!,the transistor that was getting hot was down to an npn transistor being where a pnp should of been,i also found a 30k resistor open,Ichanged the transistor for a pnp also replaced the open resistor,now it seems spot on,i think it had been got before i got it, at as a couple of pc boards had missing screws,dare say a previous repaire attempt badly done,thanks all for your help,Paul m3vuv.73
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