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Another 7D20 attenuator question


Dallas Smith
 

Hello again,

Thanks too all for your suggestions. Finally got it to work, no errors, after polishing the substrate pads. Got no answer for my question if the substrate pads are supposed to be gold plated? I think the relay problem has always been the substrate. What goes wrong with the relays? They have anti corrosion gold contacts after all, coil?

Changed the CCD & Ram board for the remaining problems.. Now for the full calibration. Any cautions when I re-calibrate this unit? I have no experience on this unit.

Dallas


Dallas Smith
 

Another thought, I'm thinking about cutting little squares from the dual fingers from a donor time base switch and solder them to the pads for a gold contact surface.


Dallas Smith
 

Hi Håkan,
Get all the attenuator errors on boot, but all relays are good. As stated by my first post I believe that the substrate board is the cause.

I noticed that the 'A12 & A13 'substrate PCB' has tarnished relay contacts. they are a dull gray (lead?). I thought Tek gold plated PCB contacts for non corrosion and good contact resistance?
Shouldn't the contact pads be gold plated?


 

On Tue, Jul 7, 2020 at 07:32 PM, Dallas Smith wrote:


My second 7D20 attenuators started acting up.
What is the actual problem ?
Early F/W's are known to sometimes cause false error(s) during startup.

/Håkan


Dallas Smith
 

Thanks Dennis,

I do not think the problem is the relays but the substrata PCB contact area.
I get all the relay test errors which make me think the problem may be elsewhere?

I noticed that the 'A12 & A13 substrate PCB has tarnished relay
contacts. there are a dull gray (lead?). I thought Tek gold plated PCB
contacts for non corrosion and good contact resistance?
Since I have two 7D20's I think I'll have enough if any relay is actually bad.

When the 7D20 is booted up and the attenuators are tested, could the reference voltage being measured be in error because of channel level calibration error?


 

Hi Dallas,
Tek began making their own parts out of necessity in the late 1960s. Some parts such as timing capacitors had to have exceptional characteristics for the instruments they went into to meet specifications and to hold calibration over long periods of time and environmental conditions. Timing capacitors that were part of sweep circuits are a good example of a component Tek made themselves. Tek also had to make the ICs that the on-screen readout of the 7000 series used. Later they were making their own high frequency analog ICs.
I do not know what it was about other manufacturer's relays that Tek did not like but at one point they decided to make their own relays. The "relay expert" they put in charge wasn't an expert after all. The Tek made relays that went into the 7000 series instruments have been a huge problem ever since.
I have removed lots of them from plugins I reduced to parts. I must have had about 100 of them in several configurations. I manually tested a few of them before giving up on that strategy because it took so long. Instead I built a little test fixture to test them and went through them all much faster. I must have tossed about half of them as not working or not reliable.
If you send me the part numbers of the ones you need I'll see if I have any of them.
Send it to me off list at dennis at ridesoft dot com.
Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Dallas Smith
Sent: Tuesday, July 07, 2020 10:33 AM
To: TekScopes@groups.io
Subject: [TekScopes] Another 7D20 attenuator question

My second 7D20 attenuators started acting up. Cleaned relays and substrate to no avail. I noticed that the 'A12 & A13 substrate PCB has tarnished relay contacts. there are a dull gray (lead?). I thought Tek gold plated PCB contacts for non corrosion and good contact resistance? Is there a way to gold plate the contact areas. Were they ever gold? I think this is the root problem with these plugins, cleaning seems to have no effect. Reluctant to buy another unit with this factory design error.

What do you say?





--
Dennis Tillman W7pF
TekScopes Moderator


Dallas Smith
 

My second 7D20 attenuators started acting up. Cleaned relays and substrate to no avail. I noticed that the 'A12 & A13 substrate PCB has tarnished relay contacts. there are a dull gray (lead?). I thought Tek gold plated PCB contacts for non corrosion and good contact resistance? Is there a way to gold plate the contact areas. Were they ever gold? I think this is the root problem with these plugins, cleaning seems to have no effect. Reluctant to buy another unit with this factory design error.

What do you say?