B&O 3163 mx3500
 

I've always wanted one of the smaller B&O MX series tellies, when I won this set at an auction for a small sum I was over the Pennines in a flash to collect it.

The chap who sold it to me said it might be the fuse inside, I've heard that one before. Once I managed to get it up on the bench, the first thing I noticed was one of the screws securing the back was missing... oh dear.

Upon removing the remaining screws the set looked quite tidy and untouched.

Nothing looked untoward so I fitted a plug and switched on, there was a slight "humph" and nothing else. When I removed the power there the sound of a fading whistle.

Oh well, at least it didn't blow up! Eventually I managed to find the correct manual (I incorrectly downloaded the MX4000 one first) and decided to do some cold checks.

As the power supply is easily accessible I quickly checked the reservoir caps on the secondary side of the chopper transformer, C13, the 148V reservoir cap measured short circuit. I removed the power board from the set and the short across C13 disappeared. Tracing the 148V to the lower line output panel I clocked TR8 (BU508A) looking all innocent.

Once I had disconnected various plugs I was able to slide the chassis out completely and look at the underside of the board. The BU508A was easily isolated from the PCB thanks to the B&O method of soldering it onto the board (The legs pass through the PCB and bend over towards the solder pads - never seen this before).
TR8 was dead short between all 3 pins, but did it die or was it killed?

A new BU508A was fitted, removed and refitted again with the ferite bead on the base this time and I checked around the PCB for any bad joints, a couple of legs looked rough on a cap (C12 between T3 and TR8) so I decided to re-solder them, upon applying heat from my iron, a right pong ensued. C12 was not well. So it looked as though TR8 had been killed.

So with a new TR8 and C12 I powered on. This time I got a standby light, pressing the "P" button beneath the CRT and up came a snowy raster.

In the absence of the correct Beolink remote control I had to tune a test card in by altering the RF channel output on my PM5515 pattern generator and the CRT looks like a good one.

Re: B&O 3163 mx3500
 

Time may tell whether some more electrolytics need replacing. Nice set and good job! Geometry and convergence still look spot on (B&O had their tubes selected from the production line).