Hi David, My eye keeps wandering over to U40, U43, and that abortion of tantalum capacitors, and snubber networks hung on the inputs to U40, U1 and U2.
Whenever I see stuff like that, I know the engineer was getting frantic over being toasted by glitches. FF clocks just aren't at all amused when they see a glitch come on their clock, or preset/reset lines. Also, old tantalums have a habit of becoming noise sources as they short, and unshort bits and pieces of their oxide layer. I have seen a few that tested ok, except that their leakage current kept spiking and returning to normal. You might not notice that sort of behavior on a power supply bypass, but it is bound to raise an eyebrow when it happens on a logic input line, or an integrator (not this circuit, I know). Capacitors hung on logic lines are always a bandaid fix. -Chuck Harris David Garrido wrote:
Hello All, I am making a little more headway on this issue of the OVERLOAD & FAULT led’s being triggered and shutting down the system. In paragraph 3-34 on page 3-4 of the manual it states: Once U2-3 has been pulled low and a 3-9ms delay, the Operate FF J Input, U41-4 is supposed to go high. And it does, BUT the next thing in the line is a short delay caused by R121 & C43 and that signal showing up at U41-1 should be low. It is NOT and neither is the Q Output (U41-14). So I thought ok GREAT, only pin 4 should be high and both of the others must be low. Easy fix, plop in another SN74106N and I should be GTG. Not so much………..still the same issue after warm-up, the OVERLOAD led comes on, followed very shortly by the FAULT led. Now I checked U3-9, it is low and U3-8 high. Next was U4-9 and it was high and pin 8 was low. On to U40-9, it is low and pin 8 is high which is what was pushing U41-1 high. So I went and checked R121, she measured 389 ohms and C43, a 4.7uf TA, measured 5.1 with 1.2 ESR. That all seems good. BUT………………. So I decided to try putting the amp into the OPERATE mode and see if that changed the input to U41-1as it is supposed to follow the low from U3-8, it did. Yes, U3-8 is now 100mV along with U3-9. U4-9 is low and U4-8 is high. U40-9 is high and 8 is low. Now the signal at U41-4 is high as before, The signal at U41-1 is low as expected, BUT………..the signal at U41-14 did not go low following the low at U41-1. Hmmmmmmmmmmm Scratching my head……….. In summary in the standby mode: U3-9 LOW U3-8 HIGH U4-9 HIGH U4-8 LOW U40-9 LOW U40-8 HIGH U41-1 HIGH U41-4 HIGH U41-14 HIGH In summary in the OPERATE mode: U3-9 LOW U3-8 LOW U4-9 LOW U4-8 HIGH U40-9 HIGH U40-8 LOW U41-1 LOW U41-4 HIGH U41-14 HIGH I could use a little more brain power as this too seems to be a bad U41-FF, but I changed that. So unless my other U41 FF was bad in the very same way……………what am I missing???? Thoughts? Cheers, David _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
_______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
