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497p front panel cal failure (CF and Ref Lvl)

radioconnection@...
 

Happy dance. Found a few runs damaged due to capacitor leakage. One was a through hole under one of the tantalum bodies. Also lost a ground connection to an IC pin and to the common ground returns for both axial lead tantalum caps. She is calibrating and happy as a clam.

Pete

John Miles
 

Caps are on the way, but I also just discovered the 5kHz scan per division is
actually scanning the same as 50kHz per division. Wonder if that is related to
the cal problem? Decoding issue on a board I suspect?
Could be. There's a chance that you have a low-resistance condition in one of the small epoxy-dipped ceramic caps on the span attenuator board (if I recall correctly, it's been a while). They don't necessarily fail shorted, but they can load down the TTL address and/or data lines to a point where they won't reliably talk to the peripheral ICs. I would have a look at the logic levels on the relevant boards to make sure they're in range.

-- john, KE5FX

radioconnection@...
 

Caps are on the way, but I also just discovered the 5kHz scan per division is actually scanning the same as 50kHz per division. Wonder if that is related to the cal problem? Decoding issue on a board I suspect?

John Miles
 

Recap it, then follow the cal/adjustment procedure in the manual for the first LO and frequency control section and see how far you get.

-- john, KE5FX

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of
radioconnection@...
Sent: Saturday, May 25, 2019 11:19 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 497p front panel cal failure (CF and Ref Lvl)

Well, it did it once, then repeated attempts failed. Would bad power supply
bypass caps on the PC boards cause problems? I have a few caps that are open
or high ESR, all are decoupling caps on the power supply rails on various
boards. Parts on order, but won't be here until next week from Mouser. Power
supply voltages are good, and I don't see appreciable noise or ripple.

radioconnection@...
 

Well, it did it once, then repeated attempts failed. Would bad power supply bypass caps on the PC boards cause problems? I have a few caps that are open or high ESR, all are decoupling caps on the power supply rails on various boards. Parts on order, but won't be here until next week from Mouser. Power supply voltages are good, and I don't see appreciable noise or ripple.

radioconnection@...
 

The first test in the manual for the center frequency and reference level self calibration fails. Otherwise, the instrument seems to be working normally. I can't find a detailed trouble shooting chart for that error.

Any suggestions where to start?

Pete