![]() |
![]() |
![]() |
|
Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE! |
![]() |
|
Thread Tools |
![]() |
#1 |
Hexode
Join Date: Dec 2008
Location: Swinton, Manchester, UK.
Posts: 305
|
![]()
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.
__________________
Regards Mike C |
![]() |
![]() |
#2 |
Dekatron
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,203
|
![]()
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).
|
![]() |