80-Bus News


March–April 1984, Volume 3, Issue 2

Page 16 of 51

Another Hardware Tip

Here is a hardware tip that is so massively useful, and yet has never been put into print… The scenario: you’ve just built (from a kit) the latest goodie for your computer. The time comes to check the board for bad joints, etc. Problem: the board is covered in flux splashes, making it difficult to check the board properly. I have discovered that proprietary Dry-Cleaning fluid is excellent at removing (fresh) flux from boards.

The technique is simple. Hold the board to be cleaned upside down (solder side uppermost), and at an angle (with the edge connector at the top). Apply a smallish amount of the fluid to the board, enough to wet the board. Using an old toothbrush (or similar), scrub the solder joints to ensure that the flux is loosened and dissolves in the fluid. Allow the fluid to run to the bottom of the board, carrying the flux with it (now you see why the edge connector has to be at the top – flux is a good insulator!), and allow to drip off the board and evapourate. Repeat with another small amount of fluid to “rinse” the board. If, after this lot has evapourated the board is sticky to the touch, there is still some flux left on the board, and another scrub/​rinse is required.

There are several points to note: this stuff evapourates very fast, so unless you can afford to “slosh it around” work on small areas of the board at a time. Second, and more important, this stuff is POISONOUS, so make sure the room is WELL VENTILATED (don’t want to lose any readers!). Third, for some reason this only works on fresh flux: it won’t work on that board you made six months ago. This is probably due to the flux oxidising, or something.

The end result will be a VERY professional finish, and it will be simplicity itself to find bad soldered joints. I tried this on my Ram after it didn’t work first time, and was surprised how many bad joints this revealed. Once these had been fixed, I plugged my Ram back in, and it burst into life (so to speak).

CP/M 3

There has been a little discussion on CP/M 3 in this magazine, together with Mr Editor’s thoughts on the matter. I know next to nothing about CP/M 3 except what has already been said in these hallowed pages. Now some of you may be wondering why Map80 are supplying CP/M 3 when Gemini aren’t. Well the reason is simple (so I am told). CP/M 3 works with the MapRam, but Gemini can’t get it to work on their GM833 Ram Disk! Mind you, my source was rather biassed… [Ed. – Yes, it was! Gemini could have supplied CP/M Plus (that is its official name) some 18 months ago, when they had it running using multiple GM802 RAM boards. However they decided that there would be insufficient demand given the market at that time, and the costs (to the customer) involved. With the arrival of the Gemini GM862 256K board I suppose there is always an outside chance that Gemini may change their minds, but I wouldn’t hold my breath waiting ....]

Open Letter to Richard Beal & Dave Parkinson

In one of his book reviews, Rory said “oh, for a book on CP/M using Z80 mnemonics!”. Doubtless the entire disk-based readership of this magazine agreed. So some on you two, you know more about CP/M than the rest of us put together, so how about a Z80 CP/M book? (It could even be published by the 80-BUS News Publishing Company Ltd Plc Inc…).

Page 16 of 51