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My Tek 2235 has a problem, The input signal on Ch1 also is displayed by Ch2. This occurs whenever CH2 is displayed (Both or CH2 only) . It occurs even if Ch2 input is set to DC, GND or AC. When I adjust the vertical position of CH1, Ch2 moves. If I put the input on Ch2, Ch1 is not affected.

Can anyone help me troubleshoot this?

Mark,
If you don't already have the service manual, get it from KO4BB.com:

<<>>

I would assume the problem has something to do with channel switching, which is shown on the "Vertical Preamap & Output Ampl" diagram. The "foldouts lg" pdf seems to have the best scan of that circuit.
Try exercising the various vertical mode switches to make sure it isn't just dirty contacts. See if the various combinations of "CH1 BOTH CH2" and "ADD ALT CHOP" make sense in some positons and not in others--that my give you some clues.

--John Gord

--- In TekScopes@..., "Mark" <mjurras@> wrote:

My Tek 2235 has a problem, The input signal on Ch1 also is displayed by Ch2. This occurs whenever CH2 is displayed (Both or CH2 only) . It occurs even if Ch2 input is set to DC, GND or AC. When I adjust the vertical position of CH1, Ch2 moves. If I put the input on Ch2, Ch1 is not affected.

Can anyone help me troubleshoot this?

Thanks John,

I do have the service manual and I was looking at U130 & U180 pin 14. It switches between +0.70 and -0.65 when switching between CH1 and CH2 alt and chop. The panel switches appear to be noise free and the scope has low hours on it. It used to work correctly for me.

The amplitude of Ch1's signal on Ch2 is about 66% of the original signal.

Also Ch1 affects Ch2 when in X-Y mode which is the mode I need most at the moment.

It appears U130 and U180 are used to mux the 2 channels is this correct? The are marked TEK. Are these proprietary chips?

- -Mark


--- In TekScopes@..., "johncharlesgord" <johngord@> wrote:

Mark,
If you don't already have the service manual, get it from KO4BB.com:

<<>>

I would assume the problem has something to do with channel switching, which is shown on the "Vertical Preamap & Output Ampl" diagram. The "foldouts lg" pdf seems to have the best scan of that circuit.
Try exercising the various vertical mode switches to make sure it isn't just dirty contacts. See if the various combinations of "CH1 BOTH CH2" and "ADD ALT CHOP" make sense in some positons and not in others--that my give you some clues.

--John Gord

--- In TekScopes@..., "Mark" <mjurras@> wrote:

My Tek 2235 has a problem, The input signal on Ch1 also is displayed by Ch2. This occurs whenever CH2 is displayed (Both or CH2 only) . It occurs even if Ch2 input is set to DC, GND or AC. When I adjust the vertical position of CH1, Ch2 moves. If I put the input on Ch2, Ch1 is not affected.

Can anyone help me troubleshoot this?

Mark,
Yes, I think those are Tek proprietary chips.
Do you have another scope available? If so, you could follow stage by stage to see where in the CH2 chain the CH1 signal first appears.
(I assume you have done the usual check of power supply voltages. A wrong bias voltage might allow some path through the diodes or transistors used for channel switching.)

--John Gord

--- In TekScopes@..., "Mark" <mjurras@> wrote:

Thanks John,

I do have the service manual and I was looking at U130 & U180 pin 14. It switches between +0.70 and -0.65 when switching between CH1 and CH2 alt and chop. The panel switches appear to be noise free and the scope has low hours on it. It used to work correctly for me.

The amplitude of Ch1's signal on Ch2 is about 66% of the original signal.

Also Ch1 affects Ch2 when in X-Y mode which is the mode I need most at the moment.

It appears U130 and U180 are used to mux the 2 channels is this correct? The are marked TEK. Are these proprietary chips?

- -Mark


--- In TekScopes@..., "johncharlesgord" <johngord@> wrote:

Mark,
If you don't already have the service manual, get it from KO4BB.com:

<<>>

I would assume the problem has something to do with channel switching, which is shown on the "Vertical Preamap & Output Ampl" diagram. The "foldouts lg" pdf seems to have the best scan of that circuit.
Try exercising the various vertical mode switches to make sure it isn't just dirty contacts. See if the various combinations of "CH1 BOTH CH2" and "ADD ALT CHOP" make sense in some positons and not in others--that my give you some clues.

--John Gord

--- In TekScopes@..., "Mark" <mjurras@> wrote:

My Tek 2235 has a problem, The input signal on Ch1 also is displayed by Ch2. This occurs whenever CH2 is displayed (Both or CH2 only) . It occurs even if Ch2 input is set to DC, GND or AC. When I adjust the vertical position of CH1, Ch2 moves. If I put the input on Ch2, Ch1 is not affected.

Can anyone help me troubleshoot this?

Hi John,

The power supply voltages look good. -8.59, 5.2V, 8.62V, 30.07V, 102V
I checked the voltages around U130 and U180 and they appear to be as stated on the schematic.

I did verify that the phantom Ch1 signal on Ch2 does not invert when I flip the switch.

Unfortunately I don't have easy access to a scope to trace each channel.

- -Mark

--- In TekScopes@..., "johncharlesgord" <johngord@> wrote:

Mark,
Yes, I think those are Tek proprietary chips.
Do you have another scope available? If so, you could follow stage by stage to see where in the CH2 chain the CH1 signal first appears.
(I assume you have done the usual check of power supply voltages. A wrong bias voltage might allow some path through the diodes or transistors used for channel switching.)

--John Gord

--- In TekScopes@..., "Mark" <mjurras@> wrote:

Thanks John,

I do have the service manual and I was looking at U130 & U180 pin 14. It switches between +0.70 and -0.65 when switching between CH1 and CH2 alt and chop. The panel switches appear to be noise free and the scope has low hours on it. It used to work correctly for me.

The amplitude of Ch1's signal on Ch2 is about 66% of the original signal.

Also Ch1 affects Ch2 when in X-Y mode which is the mode I need most at the moment.

It appears U130 and U180 are used to mux the 2 channels is this correct? The are marked TEK. Are these proprietary chips?

- -Mark


--- In TekScopes@..., "johncharlesgord" <johngord@> wrote:

Mark,
If you don't already have the service manual, get it from KO4BB.com:

<<>>

I would assume the problem has something to do with channel switching, which is shown on the "Vertical Preamap & Output Ampl" diagram. The "foldouts lg" pdf seems to have the best scan of that circuit.
Try exercising the various vertical mode switches to make sure it isn't just dirty contacts. See if the various combinations of "CH1 BOTH CH2" and "ADD ALT CHOP" make sense in some positons and not in others--that my give you some clues.

--John Gord

--- In TekScopes@..., "Mark" <mjurras@> wrote:

My Tek 2235 has a problem, The input signal on Ch1 also is displayed by Ch2. This occurs whenever CH2 is displayed (Both or CH2 only) . It occurs even if Ch2 input is set to DC, GND or AC. When I adjust the vertical position of CH1, Ch2 moves. If I put the input on Ch2, Ch1 is not affected.

Can anyone help me troubleshoot this?