7A13 relais
The Tektronix 7A13 differential/comparator plugin has a large number of relais inside. And those relais are known for failing. They use several versions of the same relais. They are in base the same, they only leave out some parts.
They are not repairable, at least, not official but if you have a few dead ones you have nothing to loose. There are 2 problems I had with them. One with bad contact resistance and 3 with dead coils. (one was a spare I used to look for the best way to open it and that is killed in the action)
The construction is nice looking but not very sturdy, so be very careful pulling them out of the sockets because the pins are part of the “contacts” and the slightest rotation makes them useless.
The good news is that you can repair them. As you see in the picture the coil is connected to the pin by wrapping it a few ties around. The wire is very, very thin, the insulation is very heat-resistant. I think they spotwelded it to the pin. In my case the wires both where broken just above the pin for number one and just after where they are melted into the plastic base for number two.
They are hard to solder because the force from your tweezer is high enough to cut them in two. And to make it even harder, the plastic will melt if you heat it to long. So I first soldered a strand from multi-strand wire to the pin and then winded that a few turn around the “T” at the top. Ten I soldered the coilwire to that strand.
The picture is from the relais that had the bad contact resistance. I solved that by “remodeling” the contact (that was clean by the way)
To open the relais I used a mill, but you can use a file too. Open it very careful. I milled a slot around the base. That is the place the cap is glued to the base. If you are almost through, stop and put the relais with the milled base into a vise and use a minimum amount of force to “break” the cap from the base. Sounds a bit harsh but this was the way that worked best for me.
This because the contacts are pushed by the metal things operated by the coil and touch the cap. You will damage them, and bow the contacts, if you mill it all the way. But be very very careful while breaking it. Looking angry at them is enough to kill them….
It took me a while, around 1 hour for 1 relais. So take your time. But most important, my 7A13 is now working again.
