RC2019/03 update 5: Video Genie cassette interface fixed!

This is part of a series for the Retro Challenge 2019/3.  Visit the index page for all the posts.

In my last post I tried (and failed) to fix the 9v voltage regulator circuit for the cassette interface on one of my Video Genies.

Today I had another go.  (Spoiler) I fixed it!

This makes me very happy as analogue electronics are definitely not my thing.  I even managed to (mostly) understand the circuit operation.  This whole repair process has been great, as it’s pushing me outside my comfort zone, and getting me to learn lots of new things.

I still haven’t quite got the cassette deck working, but I have a plan.

Here’s the 12 minute video:

The next thing is to replace the drive belt in the cassette deck.

In the video I had vaguely measured the belt at about 24-25cm.  I found a guide online that suggested feeding string through the belt path, measuring that, and then deducting 10% to get the correct tension.

I did that and got 249mm circumference (making my estimate look pretty good!)  10% off gives 224mm.

Looking online, some sellers quote the ‘folded’ length (presumably half the circumference?) or the diameter.  I’m not sure how you’re supposed to measure the diameter of a flexible belt!  Still, 224mm circumference is about 71mm diameter.

I’ve ordered a pair of 70mm diameter belts, which should arrive by the weekend.  (The second belt is for the other cassette Genie that I found also has a loose belt.)

I also ordered a new switch (one of the Genies has a broken ‘Video Cut’ switch at the back).  This puts the video output into a split screen mode (left or right pages of 32 wider characters rather than one page of 64 characters).  It’s very rarely used, as it’s not a very useful mode.  But since I’m fixing everything else, I might as well replace it.

I’ve also order a load of knobs.  All three Genies are missing the knobs off the buttons on the back.  I have a very clear image in my head from 38 years ago of what those knobs looked like, so I’ve managed to find something very close (I hope).

More to follow next weekend :-)