Hi Mark,
On Fri, 07 Feb 2025 05:03:31 -0800
"atlasstuff via groups.io" <g4fph@...> wrote:
I could not see a way of having the Transmit Exciter Board on extenders at the same time as keeping the radio running using the Jumper Board to replace the DR7 / Display Board. Did I miss a trick here?
The trick is to power the board up on the bench from a 10V power supply. You can do a lot of troubleshooting this way.
My attitude to parts replacement - especially capacitors - is hardening. I've never been fond of blanket / just in case replacement, but tantalums can cause a lot of collateral damage and undeserved misery when they go short-circuit. Generally, if I pull a capacitor out to test, these days, I replace with new regardless of the test results. In this case, I replaced old tantalum with new tantalum. If I had had low-value electrolytics to hand, I would probably have used those instead as it was an LF / audio application.
Good detective work. I think I would have looked at the ceramic coupling cap first. They can go bad or become microphonic. Tantalums have an undeserved bad rap. They are very reliable unless they have been abused. High surge current, reversed polarity, and excessive soldering heat are the most common forms of abuse. It would have been interesting to find out if one of your tants is actually failing.
Before re-installing the DR7, I changed the key electrolytic capacitors around the power feed in and the two 5 Volt regulators on this board.
Some years ago I decided to completely re-cap one of my TR7s just to see if I could notice any difference. I did not. AFAIC the only "must replace" capacitor in the TR7 is C2108 on the power supply board. It WILL fail sooner or later and strange things will happen.
Will try drilling them out. If that doesn't work, push out the PEM nuts using a hydraulic press and try tapping the holes left behind in the chassis for some suitable metric screws.
that probably won't work well. There was a reason Drake used PEMs there. Full disclosure, I detest PEMs. However with aluminum that thin your tapped threads will be very weak, if you can get any cut at all. Sheet metal screws would do better but would be easy to over-tighten and strip out.
--
73
-Jim
NU0C
Jim Shorney