Oscilloscope Channel 1 problem on BK Precision model 2120

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This 2nd handed oscilloscope's channel 2 is in function but the channel 1 found no reaction to signal input.
The channel 1 can shows the beam line and can be positioned up and down.
Is there any link I can download the services manual or schematic?
Or could anyone give me some guidance to repair the fault channel.
Thanks very much in advance.
:confused:
 
most common problem with scope inputs is either an open resistor in the attenuator switch, or a blown diffamp transistor. the input amp of an o-scope is very much like in an audio amp, a diff pair with a current source. the diff amp feeds symmetrical VAS stages all the way to the deflection plates. between the input and diff amp, you have a stepped attenuator. if your trace can't be centered on the screen, suspect the amp section. if you can center the trace, suspect the attenuator.
 
BK precision 1477 auto sweep

I have an old BK 1477 scope. Most functions seem to work okay, but the auto-sweep does not trigger any horizontal trace. If I connect a signal, I can trigger on it but the "auto" trigger does not function. Can anyone give me a hint on repair of this issue? Thanks.
 
I have an old BK 1477 scope. Most functions seem to work okay, but the auto-sweep does not trigger any horizontal trace. If I connect a signal, I can trigger on it but the "auto" trigger does not function. Can anyone give me a hint on repair of this issue? Thanks.
I would like to get back to this little scope.

see previous post:
I would like to fix the auto sweep mode.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.