Nak ST-7 circuits or repair info please - Page 2

anatech · 2nd September 2007, 11:42 PM

Hi MadMutt,
See all that dark brown "glue"? Remove it. It can go conductive and corrosive.

Quote:

Guess that means the vfl is shot.

No, not unless the filament is open. Check for your voltages (compare). Check the display uP is running (need 'scope). It might be fine once you clean it up.

-Chris

MadMutt · 3rd September 2007, 12:22 AM

Only gorilla snot I see is on the back of the display board. (cable anchoring)
I shall remove it.
Will post back when done and tried.

Any idea which pins on the display are the heaters ?
Wondering if I can check the actual display.

Only hiccup is that the two ST-7's I have are ever so slightly different in wiring.

Good display in bad unit = good.
Bad display in good unit = bad.
So the fault follows the board.

Might even swap the main i.c over as an acid test.
If I get crazy I could even swap the vfd over, but I'm hesitant as I don't want to damage the good one.

Oh, I do have a scope too.

anatech · 3rd September 2007, 12:38 AM

Hi MadMutt,
The two pins on the outside are generally the filaments. Often two are shorted together on each end, look at the leads. If you unplug the board, compare the resistance between those two points on both boards.

-Chris

MadMutt · 3rd September 2007, 01:05 AM

Compare with other board.
Yes.
I'm obviously having a 'blonde' day.

So obvious yet . . . . . .

anatech · 3rd September 2007, 01:10 AM

Believe me, we all do!

3rd September 2007, 12:38 AM	#13
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi MadMutt, The two pins on the outside are generally the filaments. Often two are shorted together on each end, look at the leads. If you unplug the board, compare the resistance between those two points on both boards. -Chris __________________ "Just because you can, doesn't mean you should" © my Wife

3rd September 2007, 01:10 AM	#15
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Believe me, we all do! __________________ "Just because you can, doesn't mean you should" © my Wife

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3rd September 2007, 12:22 AM	#12
MadMutt diyAudio Member Join Date: Nov 2006	Only gorilla snot I see is on the back of the display board. (cable anchoring) I shall remove it. Will post back when done and tried. Any idea which pins on the display are the heaters ? Wondering if I can check the actual display. Only hiccup is that the two ST-7's I have are ever so slightly different in wiring. Good display in bad unit = good. Bad display in good unit = bad. So the fault follows the board. Might even swap the main i.c over as an acid test. If I get crazy I could even swap the vfd over, but I'm hesitant as I don't want to damage the good one. Oh, I do have a scope too.

3rd September 2007, 01:05 AM	#14
MadMutt diyAudio Member Join Date: Nov 2006	Compare with other board. Yes. I'm obviously having a 'blonde' day. So obvious yet . . . . . .

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