On Thu, Jul 17, 2025 at 10:00 AM paul swed <paulswedb@gmail.com> wrote: > Tom check to see if the 10 MHz feeds the 100 MHz multiplier. I think that > ultimately drives the system. > Without the board I think the clocks are missing. > Of course! I should have thought about that. Right now, I don't even have anything on the "INT" or on the "EXT" test points on the A8 reference frequency buffer board. At least that narrows the issue down to this board only for now. I don't see anything obvious on the board where a failure would result in shorting the +15V, but one useful thing is that the +15V is only used when there's an EXT clock in play. So I could disconnect the +15V (e.g. by removing R16 in the ripple filter) and then check if the INT clock comes through. Thanks! Tom

Tom I have seen the caps short and no smoke. There are 2 15V caps C17 before R16 and C16 after. Either could cause the issue. Simply lift a lead on both caps and see if the system works. Paul WB8TSL On Thu, Jul 17, 2025 at 1:36 PM Tom Verbeure <hombre@gmail.com> wrote: > > > On Thu, Jul 17, 2025 at 10:00 AM paul swed <paulswedb@gmail.com> wrote: > >> Tom check to see if the 10 MHz feeds the 100 MHz multiplier. I think that >> ultimately drives the system. >> Without the board I think the clocks are missing. >> > > Of course! I should have thought about that. > > Right now, I don't even have anything on the "INT" or on the "EXT" test > points on the A8 reference frequency buffer board. At least that narrows > the issue down to this board only for now. > > I don't see anything obvious on the board where a failure would result in > shorting the +15V, but one useful thing is that the +15V is only used when > there's an EXT clock in play. So I could disconnect the +15V (e.g. by > removing R16 in the ripple filter) and then check if the INT clock comes > through. > > Thanks! > Tom > >

Power rail shorts are typically shorted tantalum caps. The yellow cylindrical ones are the most notorious for that, but other form factor Ta caps can also cause it. Wilko > On 17 Jul 2025, at 22:18, Tom Verbeure via time-nuts <time-nuts@lists.febo.com> wrote: > > On Thu, Jul 17, 2025 at 10:00 AM paul swed <paulswedb@gmail.com> wrote: > >> Tom check to see if the 10 MHz feeds the 100 MHz multiplier. I think that >> ultimately drives the system. >> Without the board I think the clocks are missing. >> > > Of course! I should have thought about that. > > Right now, I don't even have anything on the "INT" or on the "EXT" test > points on the A8 reference frequency buffer board. At least that narrows > the issue down to this board only for now. > > I don't see anything obvious on the board where a failure would result in > shorting the +15V, but one useful thing is that the +15V is only used when > there's an EXT clock in play. So I could disconnect the +15V (e.g. by > removing R16 in the ripple filter) and then check if the INT clock comes > through. > > Thanks! > Tom > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com

Not everything is solved, but I have the 5370A up and running! * I first disconnected R16 to decouple +15V from the board. After that, I had an ECL clock on the INT test pin, but no clock to A9 because the board uses +15V for the ECL to TTL conversion. * Then I noticed that C17 was indeed burnt. I replaced that with a different cap and put R16 back in place, but now R16 went up in smoke! So there's definitely still something wrong on the board. * My speculation was that the ECL2TTL converter was fine but the 5/10MHz ext clock to ECL conversion was not. So I removed R16 again, disconnected R14 (of the ECL2TTL conversion) from its local +15V rail and bodged it to the incoming 15V on the connector. * After this, it worked! The remaining issue now is the ext clock to ECL conversion. This needs to be fixed if I want to use my external 10MHz reference. There's really not a lot of components left that can be broken... I will also replace the Comcor mains input block. I'm convinced now that its RIFAs are the ones that created the smoke (and the smell.) The 5370A has more than enough room to put in a replacement that needs more depth to attach the connections. Tom [image: hp5370a_showing_a_result.jpg] On Thu, Jul 17, 2025 at 11:45 AM paul swed <paulswedb@gmail.com> wrote: > Tom I have seen the caps short and no smoke. There are 2 15V caps C17 > before R16 and C16 after. Either could cause the issue. Simply lift a lead > on both caps and see if the system works. > Paul > WB8TSL > > On Thu, Jul 17, 2025 at 1:36 PM Tom Verbeure <hombre@gmail.com> wrote: > >> >> >> On Thu, Jul 17, 2025 at 10:00 AM paul swed <paulswedb@gmail.com> wrote: >> >>> Tom check to see if the 10 MHz feeds the 100 MHz multiplier. I think >>> that ultimately drives the system. >>> Without the board I think the clocks are missing. >>> >> >> Of course! I should have thought about that. >> >> Right now, I don't even have anything on the "INT" or on the "EXT" test >> points on the A8 reference frequency buffer board. At least that narrows >> the issue down to this board only for now. >> >> I don't see anything obvious on the board where a failure would result in >> shorting the +15V, but one useful thing is that the +15V is only used when >> there's an EXT clock in play. So I could disconnect the +15V (e.g. by >> removing R16 in the ripple filter) and then check if the INT clock comes >> through. >> >> Thanks! >> Tom >> >> >