Tek 2215. Vertical Amplifier Issues.

[M3VUV51]

I find it odd that I get almost a dead short to ground on WW985 but a reading of near as dam it 5V when it's powered on!

[frsimen]

Check the resistance from WW985 to chassis with the meter's probes connected both ways around. If both readings are low resistance there is a problem. I expect you will find the resistance is much higher one way than the other. If that were a genuine low resistance, the voltage regulator would go into current limiting, which it isn't doing.

As the horizontal shift isn't working, it would be worth starting at that control and moving stage by stage through the X preamp and X amp stages. At each stage, check the transistor voltages against those on the circuit diagram. Try adjusting the horizontal shift as you go along, as you did with the CH1 shift.

You may find that several components have been damaged but if you work through the circuit carefully you will have a chance of repairing this.

[M3VUV51]

w985 measures with -ve probe on tp500 =240 ohm.test leads reversed =240 ohm.w985 from chassis ground ( -ve probe on ground =153 ohm,test leads reversed =152 ohms

[PJL]

Originally Posted by M3VUV51

no hoz shift, no tb whatsoever no xy but it does display a dot in xm mode dot doesn't move with inputs

PSU seems to have survived. Make sure the scope is setup OK, channel 1 only, horizontal mode A, A trigger Auto, SEC/DIV set to mid position.

Do you mean there is no horizontal display except in xy mode when it displays a dot but that does not move with the horizontal or vertical positions
pots? or... have you done other checks that show the timebase is not running?

I need to look at the xy mode to see how it works but that dot may eliminate quite a bit of 'stuff'.

Is the 'triggered' lamp lit?

Do you have a working scope?

PS: Channel 2 position controls the horzontal position in XY mode.

[PJL]

If in XY mode you can move the dot around using channel 1 and channel 2 position controls then we know the vertical and horizontal amplifiers and plate drivers are all OK. We would then need to move on to the A sweep and this is where another scope would be useful.

[M3VUV51]

I can only move the two dots up and down in XY mode with the beam finder pressed, nothing I do moves it horizontally. Yes I have another 50MHz scope analogue and DSO. Also the trigger light won't come on no matter what I do.

[PJL]

I suggest staying with the XY mode and adjust the channel 2 position looking for changes:
First when measuring the horizontal plates.
If neither change then when measuring Q736 base.

In all cases record the actual value and if the value changes with the pot.

[M3VUV51]

Well the measurements between the horiz def plate wires are horiz pos control fully ccw=-22.43 fully cw=27.06, I cant locate Q736 yet to measure it, there is only one horizontal pos pot that serves both channels.

[PJL]

That looks good but did you do this in XY mode as I expected the channel 2 vertical position pot to change the horizontal position in that mode. If it does then it looks like we need to move on to the A sweep.

[M3VUV51]

Can anyone spot Q7336 or am I going blind?

[PJL]

If XY mode appears to be OK...

On page 161 of the service manual you can find the test procedure for Sweep A. Make sure you have set the controls up properly and have provided an input from a sig gen as described. Can you get the TRIG,D lamp to operate now? If not then we need to look in the TRIGGER section on page 160.

[M3VUV51]

im more concerned with testing around q736 first as i guess if the horiz amp is goosed it mat be triggering but cant display it due to the horiz amp not working,ie pos etc,my biggest issue is not beeing able to spot q736 on the pcb layout pic in the manual or actualy on the physical main board in the scope.

[PJL]

Don't worry about Q736 do the XY test as this will prove Q736 is working. The trigger is clearly not working as the lamp is not coming on so the sweep is not running. That is why we are using the XY mode for tests of the vertical and horizontal amp.

PS: The vertical and horizontal amps will not effect the sweep operation.

[RogerEvans]

Q736 is on the A12 board, 'Attenuator / Sweep Board'. I haven't found the component layout diagram yet.

Roger

[PJL]

The short was probably on the main board as that's the one on the base of the scope. The Trigger circuitry is on that too.

[RogerEvans]

The Main Board is quite large, do you have any idea which part might have been in contact with the solder?

Roger

PS Sorry PJL, I didn't immediately spot the reply was from you and not the OP.

[M3VUV51]

well q736 base measures with horiz pos control fully ccw-827v, fully cw -8.24v

[M3VUV51]

i may start pulling transistors and testing them,can someone give me a good starting point?ie q whatever or board ref a1 etc,im talking about the main board here ok .

[frsimen]

That is not a good approach, you'll just end up causing damage the PCB.

Follow PJL's very sound advice to stick with X-Y operation.

You have another oscilloscope, so you can use that to trace signals through to see where things are going wrong.

Study the block diagram of the oscilloscope in the manual which will show the path of signals when in XY mode. The circuit diagram will then make more sense. Apply a signal to the channel which is used for the X input. If the calibrator is working, use that as the signal source. You can then follow the signal through the various stages.

If at some point the signal stops, that's where you should start looking for a faulty component. Leave the desoldering tool on the shelf until you have an idea of where you should be looking.

As always, slow an methodical is the way to go, there are no short cuts!

[PJL]

My recommendation is we test the vertical and horizontal amplifiers first and that requires the scope to be setup in XY mode (see page 30). XY mode is selected using the A SEC/DIV control. You should be able to centre the dots using the channel 1 position (vertical) and channel 2 position (horizontal). If this works then injecting a signal (you can get 50Hz by simply holding the probe with your fingers but you may need to adjust the VOLTS/DIV) on channel 1 should result in a vertical bar, and channel 2 should show a horizontal bar. If this test passes then we have working channel and vertical and horizontal amplifiers so can move on.

The next stage would be to get the Trigger working as without a trigger you will not get a sweep. To complete any trigger test the scope must be setup correctly as on page 161. It might be worth posting a picture of the scope front panel so we can confirm it is correct. If we can confirm the trigger is definitely not working then it would be worth inspecting that area of the circuit board looking (or smelling) for 'cooked' components.

This is a complex scope with many parts so we will need to be methodical.

PS: posts crossed with Frsimen
PS: You can use the probe adjust for a signal