25c

[Geoff Quickfall]

The two 'rivet tabs' take a lot of stress. I have found many continuity faults between the rivet contact and the PCA. I have found many attempted repairs with huge globs of solder.

Test:
- remove the battery pack.

- jump with wires directly to the rivet contact and try calc.

- no joy, remove the PCA from the shell.

- continuity test the rivet contact to a point further in the PCA.

- no continuity tester (ohm meter) then jump the power to a point just after the contact rivets on the PCA trace.

- typically the rivet contact is no longer contacting the PCA trace.

Repair:

- remove excess solder using flux to penetrate the rivet contact and trace interface.

- clean rivet contact with fine fibre brush or wire brush trying to avoid PCA trace.

- add flux and a small amount of solder to the PCA trace and rivet contact to establish new connection between them.

- confirm connection with continuity tester.

- reassemble and test.

- no joy and continuity between rivet contact and PCA is now good, then problem further up the PCA.

So a clean PCA usually means a bad rivet contact or a bad ACT. That, of course, after establishing no corrosion or oxidation damage. The rivet contacts may look good but under 40 years of battery changes and continuous flexing, they fail. The second failure other then a bad ACT is the board under the large resistor. This resistor warms up and cooks the PCA board to a nice well done toast look and may fail itself.

I have resurrected three non working 29c and a few 25s by correcting the contact rivet continuity.

Geoff

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