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Tektronix 7A16A Low Bandwidth Issue

Bruce Atwood
 

Sounds like there could be a problem with the bandwidth limit switch or
circuit.

On 12/19/2019 1:15 PM, kdlamet@... wrote:
First I come here a lot for the great info, but seldom if ever post. I recently picked up a non-working 7904 from eBay and was able to repair the 670-1613-00 HV board. After getting it working I began collecting and repairing Plugins.

I had pretty good success until running into a 7A26 and now this 7A16A.

The issue: everything passed cal until the bandwidth section. Using an SG503, 012-0408-00 cable and 50 ohm terminator into the 7A16A set to 10mV input range and 6 division input, it drops to less than 1div around 50 Mhz. 4.2 division occurs at ~ 28 Mhz. The SG503 and cable are working as I get good response from my 2465A.

Initially the 7A16A had bad contact on all ranges of input - cleaned ONLY with 99% IPA. Also input BNC connector had an intermittent ground - internal to the connector. This was replaced with a 7A26 donor part.
It appears to be in the Attenuator section as I see the loss of bandwidth at the output prior to going to the main amplifier board.

Any assistance/info/guidance on this issue would be Greatly appreciated.

Thanks in advance.

P.S. A little background.... 40+ years Electronic Technician - Private industry / DOD. No Engineering. I've fixed it all Radios/TV/Auto Stereo/RADAR/Test Equipment(PMEL).

-Dave



.
--
Bruce Atwood PhD
Department of Astronomy
The Ohio State University
100 West 18th Ave., Room 4055
Columbus, OH 43210

Phone 614.314.0189
FAX 614.292.2928

Eric
 

Have you tried a calibration from the service manual. I know when I started
out my missing bandwidth was in the high frequency compensation of the plug
in. It is a really finicky calibration and you need a really fast edge
squair wave. Usually from a tunnel diode pulser. For over 1 ns rise time a
106 or a pg506 will work but that is just good enough for a 7a26. their
rise times are 1nS, faster than that and you are in to the world of tunnel
doides.

On Thu, Dec 19, 2019, 2:35 PM <kdlamet@...> wrote:

Correction: cable number is 012-0482-00.