7A26 transient response 5 nS all atten

Jean-Paul
 

Hello all: My workhorse 7A26 needed rework, in 7804 mainframe.
Cleaned the AC/DC/GR contacts on attn with the iso alcohol-paper strips, and exercised some scratchy controls.
Poor fast transient response on CH2, same dip and peak ~ 5 nS at ALL V/div.

Setup: Leo Bodnar pulser 40 pS>Mini Ckt HAT-15>>Mini Ckt HAT 20>>precision 50 Ohm thru>>7A26 input
Same result if 7A26 is in L or R side 7804.
Shots are: Affected 7A26, CH2, CH1, Good 7A26 Ch2 Ch1
http://crypto-museum.org/TEK/7A26/7A26.pdf

Since the aberration is constant on every V/DIV, the attenuator and 2X amp seem to be exonerated.

Before I dare probe the CH 2 amp circuit, a few questions please:

1/ Test points mentioned on schematic are NOT in PCB photos, only the parts numbers. Need a board layout with test pts.
2/ Using normal P6137 probe. placement of ground lead ?
3/ Precautions in probing around the custom TEK hybrid ICs, eg U2350, U2450?
4/ Serial: Manual has sch versions for SN B179999 < and B180000>.
My other 7A26s have this format SN, but this has no letter, 708058. I think its a late model, but see no IC date codes.
Readout PCB is 672-0051-13 Amplifier PCB is 670-2549-21 attenuators are PN200-1442-00

Hope to receive some tips from our TEK veterans!

Jon in Paris

Join TekScopes@groups.io to automatically receive all group messages.