Marconi TF2370
 

On Sunday I wasn't making good progress and added my tuppence worth to this "I'm an Idiot" thread after killing a regulator chip.

Well my replacement linear regulator arrived today which is a 10 pin circular can and not too easy to replace a second time with tracks falling off the board but after that I was still struggling to identify why one of the 5 volt rails was shorted.

The TF2370 is in two halves and fortunately it can be powered up with the RF section unplugged. Even with all the plug-in cards removed from the digital chassis I still had a short circuit and it wasn't obvious to me where else this rail supplied. There is a thyristor over volt protection on the rail but disconnecting that I still had a 0.3 ohm short.

Some of the wiring harness has rather tightly packed connections in places and with shaky hands and poor close vision I was a bit reluctant to unsolder parts of it but desperation forced my hand and I eventually tracked it down to the front panel and to one of the push button switches. I thought this was a bit odd but on turning it upside down I discovered that there was a ground wire with the insulation cracking off. In an instrument that is entirely wired in plastic coated wires this was a big surprise.

Anyway, I glad to report that the old TF2370 back in operation again.

Peter

Re: Marconi TF2370
 

Well done, they are nice units!
On a sort of similar vein.
The other day, on a pair of joined phono to phono leads...I had slightly intermittent audio but not totally dissapearing on one channel, the audio was dropping a few dB, after half an hour of moving cables around and twisting and pulling them, I found a cable had more or less disintegrated inside partially shorting the inner conductor to the outer screen (this was discovered only after I decided to cut it open).
These were moulded grey Phono to phono cables from the early 70's at a guess.
Life is a gas, or is it a beer? :beer: