Microvitec Monitor 1451MS4

The Microvitech monitor is a well-known classic from the 1980s, synonymous with the BBC Micro computer of the same era. It’s distinctive design, being manufacture in a metal cabinet, provides a robust yet attractive appearance. This has also ensured these have survived general wear and tear down the decades, all this making them a much sought after monitor.

Having recently obtained a BBC model B and Teletext adapter, I also wanted to complete the set-up, with a Microvitech monitor. As mentioned above, as these are fairly sought after, this in turn has pushed up the prices. Looking around, I found one for £300 less delivery and one for £45+£10 postage, non-working. I decided on the latter, not only a possible bargain, but we like to repair things around here.

I contacted the vendor expressing my interest and concern about damage in transit. The vendor assured me it would be packed accordingly, and they had shipped many such items before. True to his word, the item turned up, safe and sound and professionally packed to withstand the trauma of transit through our modern “don’t care postal system”. Now to get to work and see if I’ve found a £50 bargain, or a heap of trouble.

Monitor Model numbers, what do they mean?

Models 1431 & 1432 resolution of 452(H)x585(V), DOT PITCH 0.64mm

Model 1451MS4 resolution of 652(H)x585(V), DOT PITCH 0.43mm

Models1441 & 1442 both with a resolution of 895(H)x585(V), DOT PITCH
0.31mm

Model 2030 Resolution of 505(H)x585(V) elements, 80 characters on 6 dot, wide matrix, DOT PITCH
0.8mm

Model 2040 Resolution of 940(H)x705(V), DOT PITCH 0.47mm

The monitor was described as power indicator light on, but monitor totally dead, I wanted to see how dead. As power had already been applied I first checked the three fuses, these were OK, so I then plugged in myself. Well, it’s not totally dead, I have all the rails 200V, 124, 12V, 5V and 24kV final anode, just a blank screen, no vertical or horizontal deflection.

R235, the 10R fusible resistor, was found to be open.  I thought it worth replacing to see if this cured the problem. The answer to this was a resounding no! The replacement glowed cherry red. Lifting one end of D302 stopped this, it’s looking highly probable the TDA1170P ic has failed.

Television Servicing article

As well as having the Microvitech service manual (available in this site’s data library) there was also a very useful article from August 1992, Television magazine, (see below). Armed with this, the investigations began.

To be continued …..

Everything was pointing towards the fault being the vertical deflection IC, TDA1170. First I replaced R235 10R fusible and recapped the important electrolytics, finally replacing IC301.  Happy days, the 1431MS lives, and boy does it look good. Thanks to all the lads in the forum for their ideas.

This completes the project BBC Model B & Teletext adapter project. Hopefully, something special and related will be coming soon, a big learning curve with that one though, all to be revealed in due course……