Mark Zacharias wrote:
OK, so it appears there is very little to discuss on this group in areas
like repairing audio components, amps, receivers, power supplies, etc these
days.

I "tune in" here almost daily and rarely find anything of interest to me.

Maybe we could share some "war stories" of cool repairs we have done in the
past.

Re-live some past glories?

The first time you traced down a bad reset line for a microprocessor?

That integrated amp that blew a channel about once a year until you caught
that bias diode occasionally opening up?

Sansui 5000A's? (yuck)

Crappy Euro caps in Tandberg tape decks?

Those times you sweated whether you could even get this thing put back
together?

Any more recent successs stories to brag about?

C'mon, don't we all enjoy patting ourselves on the back, really?


Mark Z.


I was in a block of flats to look at a curious problem in their terrestrial TV reception. Whenever the communal stairs/hall lights were on, all TV sets in the block lost signal.
The stairs lights were controlled by a timer relay that kept the lights on for a few minutes after any push button was hit, so every time someone entered and hit the light the neighbors TV signal went out for a few minutes.

I started checking the terrestrial antenna head amplifier and found it lost mains power whenever stairs lights were on. I also observed that four or five lights in the stairs did not illuminate and some push buttons didn't activate the lights. That one had me thinking for a while and I drew this diagram to understand what could possibly be going on the

Head amplifier wall plug
N L
| |
| |
|--light bulb--| |
|--light bulb--| |
|--light bulb--| |
X | |
|--light bulb--| |
|--light bulb--| |
|--light bulb--| |
| | |
| relay |
| | |
| +-----+
| |
N L
Mains supply

That turned out an accurate representation of the problem, I found "X" was a badly burned electrical terminal inside a connection box. With relay open, the bulbs happened to be in series in the neutral going to the head amplifier and because its small current draw it had enough voltage to work. With relay closed, only light bulbs before the break illuminated and the head amplifier got the L pole in the N wire through the non-working bulbs, so no voltage to work.