Re: B92A no sweep


On Tue, 14 Feb 2017 04:01:49 +0000 (UTC), you wrote:

Thanks David,I have re-seated everything I could find, I am using an extender I just built from John Griessen.
That is going to make things a lot easier.

Cam switches are all in good shape and properly functioning.
I didn't know if there were any known issues with the 7b92a.
There are no special issues that I know of.

From what I can read, they seem pretty reliable.
They are pretty complex though. The problems I have seen are shorted
tantalums and mechanical problems with the cam switches.

I know there is some mention of the sweep generator 155-049-02, but I am not sure how to diagnose it's proper function or if it's even suspect.

Thanks for the thoughtsBrent
On 14 Feb 2017 04:16:50 +0000, you wrote:

I forgot to mention that, initially last week the problem began with the sweep working fine for the first 30 seconds and then quit. It might come back for a few moments, even another 30 seconds on occasion before not working at all: I assumed from a component warming up. This week however it has not worked at all. I was able to use a thermal camera to look at heat on the boards and found nothing unusual.Whatever it is, it isn't intermittent any longer.
The problem before the unblanking was lost might simply have been the
sweep signal getting lost between the output of the sweep generator
and the horizontal amplifier. The alternatives are much more complex.

I had an idea which might apply to before the sweep vanished; if the
sweep was being displayed as a dot which gets wider as the sweep speed
is increased, then the unblanking is working and probably the sweep
integrator is working. The odd part is that the sweep reset was
apparently also working even though the sweep was never reaching that
point and to me that points to a problem with the end of sweep
comparator continuously indicating the end of the sweep.

The good news, if it can be considered that, is that the sweep
generators are all discrete. The bad news is that the loss of
unblanking (and loss of triggering?) indicates a larger problem.

Before getting too involved going through the circuits, I would make
measurements of the supply voltages on the boards. Maybe one of the
power supply decoupling networks gradually failed.

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