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Diagnosis and Repair of a Commodore CDTV unit which has a strange ‘3FFF’ problem.
In the first part, below, I diagnose. In the next part (coming soon, will be added here) I repair.
https://www.youtube.com/watch?v=KtxYHoK8vFg
It’s a chore to find yourself lugging junk down to the tip. But every now and then you happen across a diamond in the rough! Today was my day to score as I spotted a Commodore CDTV unit lurking in a dark corner of the electrical disposal area. She was looking poorly and in desperate need of rescue. Needless to say I took on the challenge, plucking her from the ruin (yoink!) and saving her from certain destruction. I am now the proud owner of a CDTV unit!
Well… no, she didn’t. Completely dead. Hence the throw-away, I presume. But no self-respecting nerd would give up this easily; I released the top cover and had a bit of a poke around. The fault was actually quite easy to find – a 5A fuse on the secondary side of the PSU was blown. Of course, a blown fuse is rarely the root cause of the problem – usually some other fault is to blame. In this case, though, I replaced the fuse and Bob’s your uncle – she powered straight up!
That was my first observation, too. CDTV units had a cool CD boot screen with a spinning disc and a laser. This unit was just booting to a kickstart 1.3 floppy screen. How disappointing!
I noticed that the unit had a clunky old switch hanging off the rear. This was clearly a poorly implemented modification by a previous owner. An obvious application for a user-installed switch would be some kind of ROM-switcher, so I began to wonder if this was the case here. The switch terminated at a 3-pin molex, but it wasn’t connected anywhere and nor did there appear to be an obvious place for it to go on the motherboard. Eventually, though – after quite a long period hunting around the motherboard and scratching my head – I found JP15 which is an in-line 3 pin header. It wasn’t a molex receptacle but the pitch looked about right. Tried it on for size and it was a perfect fit!
A couple of power cycles with each position of the clunky switch finally revealed the classic CD boot screen. Even by today’s standard it looks uber-cool. This photo doesn’t really do it justice:
So, I am now a very proud owner of a Commodore CDTV. She’s not the best of examples (the reset button on the front is broken and the keyboard is a bit worse for wear) but she’s fully functional and I reckon she’ll make a nice base unit for some hardware hackery. It’d be nice to bring some modern computer peripherals to this machine and see if I can get them working together with her. A hard drive would be nice, for example. Hmmmm! To be continued!