NOS Dana 1992 just went crazy - fixed - broken CPU

[mikerj]

The difference between the NOS and original CPU is interesting considering they are only ~18 months apart.  The dead one has notably lower quality lettering, the top surface texture is much coarser and the alignment notch doesn't seem to be nicely defined like it is on the NOS part.  Possibly packaged in different factories.

[coromonadalix]

same old model (like the defective)  here in one of my  racal 1992 .....  started one this morning, seems alive  loll

There was some of them  ceramic / gold cover plated  if i recall

[kawal]

For good measure i rechecked all caps and found the 2 caps in the +/-11V circuit to be dried up. These are 680uf/25.  I replaced with 1000uf/35 kemet 105C versions. The bad caps measured 47K ohm  ESR and 100...400pf.  I would say completely dried up.  While these where defective they do not have anything to do with the digital section but are used in the input stages.

Either way  Now the meter is completely happy.

Picture of the Dana measuring my OCXO distribution box (after warmup and adjustment). BTW the OCXO distro box matches my OCXO in HP 8901B , HP8714ET and HP Spectrum analyzer and now DANA 1992.  One day I will get a gps disciplined 10MHz reference.

[edpalmer42]

Are you aware of the sneaky trick to get one more digit on the display?  Press the up arrow button repeatedly to get to 9 digits of resolution.  Then press and hold the up arrow button for about 2 seconds.  The most significant digit will overflow off the left side of the display and you'll have one more digit on the right side.  So, in your picture above, instead of displaying .X Hz, you would be displaying .0X Hz.

Ed

[kawal]

Ed
Thanks for that info .  I knew it worked when frequency was less than 10Mhz but didn't know the trick with 2s pressing the up button.
Will try it out.

Maciej

OK  I  did try that out last night -  the Exponent changes from 6 (M) to 3(k) and the decimal point moves 3 places . The result takes about 10s to refresh and you gain  1 digit of resolution.  WOW