7704A Mainframe Panel Lights No-Op


k6whp
 

(seems like this guy is rebelling against me or is deteriorating.)

The panel light for the controls in the front middle of the mainframe are dead. That is the button lights for the Vertical and Horizontal Mode buttons have gone out. (Scope still works.) Additionally, the A and B trigger Source lights no longer work as well. Before some worked and some did not. Now the whole thing is dark.

In looking at the service manual, I stumbled onto page 6-3 and note that there are four boards ("board 11", "board 12", "board 13", "board 14" which are Vertical Mode, Horizontal Mode, A Trigger Source, and B Trigger Source respectively.) and each of these is supplied with a "+5V Lights" source from the Calibrator Board 10 but the schematic shows no originating source and I have not been inside the uni yet to see what's what.

Anyone troubleshoot this problem and can offer advise and information?

Thanks in advance.
--
William, k6whp
"A friend told me to cheer up, things could be worse.
So I cheered up and, sure enough, things got worse!"


Albert Otten
 

On Mon, Jan 1, 2018 at 10:26 pm, William wrote:


(seems like this guy is rebelling against me or is deteriorating.)

The panel light for the controls in the front middle of the mainframe are
dead. That is the button lights for the Vertical and Horizontal Mode buttons
have gone out. (Scope still works.) Additionally, the A and B trigger Source
lights no longer work as well. Before some worked and some did not. Now the
whole thing is dark.

In looking at the service manual, I stumbled onto page 6-3 and note that there
are four boards ("board 11", "board 12", "board 13", "board 14" which are
Vertical Mode, Horizontal Mode, A Trigger Source, and B Trigger Source
respectively.) and each of these is supplied with a "+5V Lights" source from
the Calibrator Board 10 but the schematic shows no originating source and I
have not been inside the uni yet to see what's what.

Anyone troubleshoot this problem and can offer advise and information?

Thanks in advance.
--
William, k6whp
"A friend told me to cheer up, things could be worse.
So I cheered up and, sure enough, things got worse!"
This can't be a big problem. Must be a bad contact somewhere, with just a very few places to check.The 5V(lights) is generated bij the SMPS diagram <8> but is also used there in the balance input to the SMPS control IC . So the source should be OK.
From there the 5V(lights) goes to the rear panel illumination on/off switch. Did you exercise that switch a few times?
Next via board 32 <9> and P32G to the Main Interface Board at <2>. The plugins get their 5V(lights) from the main interface board. So please check P32G for good contact.

Albert


k6whp
 

Albert,

You nailed it! Would have blown right by that in my rush to get to the A32 board to check the +5V supply! So, articulating it a few times brought the lights back. Talk about feeling really dumb!

Well, that gets me back to square one but with a little more knowledge than before. The individual B SOURCE TRIGGER lights don't work but I have reason to suspect that it is the +5 lights connection to board 14. One rainy weekend, I will tear down the front and poke around with a probe but, for now, that's good enough!

Sincere thanks! As good as the service manuals are, they do not seem to address these trivial problems in a readily researchable manner.

--
William, k6whp
"A friend told me to cheer up, things could be worse.
So I cheered up and, sure enough, things got worse!"


Harvey White
 

On Tue, 02 Jan 2018 17:43:38 -0800, you wrote:

Albert,

You nailed it! Would have blown right by that in my rush to get to the A32 board to check the +5V supply! So, articulating it a few times brought the lights back. Talk about feeling really dumb!

Well, that gets me back to square one but with a little more knowledge than before. The individual B SOURCE TRIGGER lights don't work but I have reason to suspect that it is the +5 lights connection to board 14. One rainy weekend, I will tear down the front and poke around with a probe but, for now, that's good enough!

Sincere thanks! As good as the service manuals are, they do not seem to address these trivial problems in a readily researchable manner.
The military, or at least the defense contractors, had the desire to
have smart diagnostics carried out by something resembling a data
tablet. You'd plug it into an aircraft, and it would interact, do
tests, and then recommend the proper repair procedure. Given the
amount of smarts in a 7000 series mainframe (and guessing how much
space is left in the only one that *had* a processor in it), the plug
in diagnostic link wouldn't be possible.

However, a decision tree on a per-topic basis would be possible, at
least to some extent. It couldn't be hosted in the scope, but could
be hosted in another piece of equipment.

Possible to do, but I'm not sure how easy. Given the basic logical
framework implementing the decision tree, you could adapt it to any
number of projects, but how close that logic could get is another
matter.

The accuracy and depth of the decision tree for troubleshooting varied
from manual to manual, if it was there at all. Lately, it of course
goes to "replace Axxx board", or "return to factory for repair".


Harvey