Thursday, May 17, 2012, 10:26 AMThis week I did some work on a Disciple disk interface which I got from Ruud Baltissen on the last retro computer fair in Maarssen.
It caused a ZX Spectrum not to boot, with garbage on screen etc.
I immediately suspected a PAL chip to be the problem.
I know from the past these died quickly in a Disciple interface, and being very expensive: MGT enabled security on the PAL chips so it was not possible to read the contents and clone them back then.
Fortunately someone once received a repaired Disciple interface with PAL chips that did not have that security, and he was able to read the contents and publish it on the net.
There is no legal limit anymore because MGT does not exist anymore, so I can happily download the PAL files.
I do not have PAL chips in stock; they're obsolete and should be replaced with GAL chips.
But the files I downloaded were not compatible with the GAL chips.
I needed to translate them.
For this, Lattice, the creators and manufacturer of PAL and GAL chips, publiced a GAL to PAL translator.
This command line utility will convert a PAL jedec file to a GAL jedec file.
I downloaded the utility, converted the PAL20L8 files, and tried to program a GAL20V8 chip with the new files.
Then I replaced the PAL chips on the Disciple, and it works!!!
So the Disciple boots again, and everything seemed fine, except for the 7805 voltage regulator on the Disciple, which is overheating.
I replaced the 7805, but it still get's to hot, possibly causing instability.
I am currently adding new cooling paste, and replacing the cpacitor at the 7805.
Hope that will solve all problems.
I suspected the inhibit and nmi buttons to have problems due to aging, so I measured the resistance: I found values of about 30 ohms.
I desoldered the switches, and measured again: no problems with high impedances.
So the conclusion is: the soldering contacts are bad.
I resoldered all important contacts on the Disciple board: all chips and more.
Now all problems seem to have gone.
So 20 - 25 years of aging of these Disciple interfaces seem to give result in bad soldering contacts! Just to let you know!
Monday, April 16, 2012, 04:44 PMI added a new page in my website: the Sales page.
From there you can easily check out my currently offered eBay items, and lot's of other rare stuff I am not (or not yet) offering in eBay, but which is available by direct order only.
So check it out (click)!
Thursday, January 26, 2012, 08:47 PMI created a document with video fixes and improvements and video cables for all ZX Spectrum 128K models.
Click here for the document.
Sunday, January 22, 2012, 07:24 AMKeep an eye on my eBay channel: http://www.ebay.co.uk/sch/quantit/m.html
I am offering lot's of rare sets the coming weeks.
On right now: a very complete boxed ZX81 set!
These are some of the items you can expect the coming weeks:
- Boxed 128K heatsink ZX Spectrums (yes, more than one)
- Opus Discovery disk systems (again, more than one)
- Disciple disk interfaces (unbelievable, even more than one of these)
- Lot's of 48K ZX Spectrums
- Interface 1 + Microdrive sets
- Original ROM game-cartridges
- ZX81 sets
- And much more....
So, put my eBay channel in your browsers favorites to not miss one of these incredible offers!
Thursday, December 1, 2011, 12:38 PMAs I had the rare and awesome opportunity to be able to buy 5 or 6 Opus Discovery interfaces this year, and because I couldn't find hires pics of the board on Google, I thought it was time to upload some myself.
Here's a video in which I'm dissassembling a floppydrive from an Opus because I forgot to set the driveselect correctly:
Here they are pics (click for hires):
Some problems I had to repair with these Opus Discovery interfaces were:
- defective rectifier
- defective ROM
- one didn't have a 6116 ram chip, don't know if it is needed, but I ordered one anyway
- one had a defective WD1770 floppy controller; replaced it with a WD1772 from an Atari ST: another model but pincompatible, and that worked great!
- one floppydrive failed, but luckally that Opus had two! Only needed to make a bracket to cover the space
- the soldered wires on the 'flying' LM317's come off easily with some movement: very frustrating when you are repairing an interface...
I encountered these interesting things:
- two had a rom v2.2 (one even had a paper with rom changes, but I didn't scan it, sorry!); the lowest rom version I found was 2.1, probably the default factory-rom
- I had one large filled floppybox with about 40 floppies filled with data; very rare to have owned as all others had only one or two or no floppies at all
- there are some different ways of how the voltage regulators are mounted
- there are some different board versions, haven't checked for numbers
This seems a lot of trouble, but believe me: ZX Spectrums fail a lot more and at a lot of more parts.
All together the Opus Discovery is a very solid system, which still works after so many years!