Sunday, December 13, 2020

Fixing an Amiga tank mouse

I recently bought an Amiga mouse on Ebay.  Unfortunately the little sucker wouldn't work in the horizontal axis.  After a little searching I found this very useful youtube video.  I plugged the mouse into my scope and saw right away that one of the photo transistors wasn't working properly. So I decided to just replace them.

So off to RS Compnents I went to get some OSRAM LPT 80 A Radial Side Lookers.

Taking the black body off was a pain in the bottom.  I DO NOT recommend trying to lever the locking parts apart.  Just try to lever the whole part up.  I broke mine and had to glue them up.



You need to put the parts together and slide them in, just really gently. The slide the wheel in really gently as well.

If you do happen to break any of the plastic there isn't much that will stick to it.  I tried Tamiya model cement and super glue with no joy.  The only thing that did work was E6000 and it worked amazingly.
I did let mine cure for 3 days before re-assembly.

Now I have another working Amiga 600 tank mouse.
 
 


Alternate parts : A new battery for my Amiga 500 memory expansion

I've heard horror stories of Amiga batteries destroying boards so I thought I'd replace mine with a coin cell battery.  It turned out that the memory expansion was in really good condition and the battery looked brand new, but still it had to go.

I ordered a replacement battery from Amiga Kit on Ebay and off I went.

First things first the RF shield has three soldered tabs to deal with.  I used my desoldering gun to get most of the solder off and then a hot iron and heaps of solder wick.  A couple of plastic spudgers are also useful to help lever out the tab while heating it with your soldering  iron.


Off with the old and on with then new.

While I was in there I decided to replace the capacitors as well.


In the end it turned out very well, although the RF case was a little tight going back on.  I didn't resolder the tabs,  I just used some Kapton tape to secure it together.


Wednesday, October 14, 2020

Amiga Backup for Disaster Recovery of CFIDE and Kernel ROM

Before I start I'll preface this entry with the fact that under Australian Copyright Law you are legally allowed to backup and restore your personally owned / licensed software for the purpose of backup and recovery for those and only those said items. This may not be applicable in your country!

The trouble with old hardware is that it fails and some parts fail more quickly than others. On one of my Amiga's I have already lost a hard drive and the kernel eprom as well.  This can be a real nightmare if you don't have a backup (I didn't so I had to buy new legal ones), so just like your photos, documents, software etc etc you should back them up!

CFIDE Backup

 If like me you are using modern Compact Flash (CFIDE) drives, it's really easy to back them up.  You will need a Memory  Card reader that supports Compact Flash and some good imaging software. Take your image and store it somewhere safe.  I keep one on my backup drive and one on a spare CF card.

Things you will need.

1) Disk Imager : https://sourceforge.net/projects/win32diskimager/

2) Generic Card reader :  https://www.officeworks.com.au/shop/officeworks/c/technology/hard-drives-data-storage/card-readers

3) Spare CF cards : I'm just using 4GB cards.

Kernel ROM Backup

Backing up your Kernel ROM is also easy but you'll need more hardware.  You need to remember to backup all of your ROM's as each model Amiga will have a slightly different one.  You will also need some spare EPROMS.

Most Amigas use 27C400 EPROM's, the A1200 apparently uses a 27C800 EPROM's.  It's a good idea to get a few and just put them away for a rainy day.  I also have a licensed multi-ROM that uses a 27C800 so I can have two ROM's on it and switch between them, it was pricey but well worth it.

Mostly the EPROM's available are UV erasable with little windows on them.  There are also some more modern EEPROM's about but none that I've seen in DIP format.

Things you will need.

1) UV Eraser : so you can erase them when you make a mistake or if they have stuff on them still.

2) Programmer : I have a GQ-4x4 with the required 16-Bit add-on board.

3) EPROMS : 27C400 for most Amigas and 27C800 for A1200's and ROM switchers

A special note: If you are backing up a 27C800 multi ROM remove the chip from the switcher and back it up as a 27C800,  don't try to back it up in the switcher!







Wednesday, September 23, 2020

Building the : SIDBlaster-USB TicTac Edition

One of the many things that I love about the C64 is the music.  I've often looked at the HardSid and wanted to get my hands on one just to play the tunes, but to tell the truth unless I listen to a real Sid next to an emulated one or for that matter a 6581 vs a 8580 I simply can't tell the difference.

In early 2019 I stumbled across the SIDBlaster-USB TicTac Edition and added it to my build list, but more for mundane practical reasons, I'd like to try to program my own emulated SID chip and try it out outside of a C64.

The project is here http://crazy-midi.de/joomla/ and the source code and pcb is here on Github

It's taken me around 7 months to build this project, with COVID-19 about it's actually been a much harder task.

The thing I really like about this project was :

  1.  The documentation,  it is quite simply amazing and every little nuance has been recorded.

The things I didn't really like were :

  1. The difficulty in sourcing the parts.  Quite a number of them were difficult to source and a one or two items aren't manufactured anymore and are quite expensive (ignoring the SID).
  2. The number of through hole parts required.

Hopefully a new iteration of this project will be updated with more current and readily available parts.

Stealing a boost converter chip for the 9/12 volt supply. 

 
Here is the finished result,  I tested it with one of my ARMSID and it works very well.
 



 


 


Wednesday, August 19, 2020

Fixing the Video on my Amiga 600, after inadvertently breaking it


A good few months ago now I recapped one of my Amiga 600's.  The caps were really leaky and it needed immediate attention. However after I recapped it I noticed a horrible blue scan line that sat at the bottom of the floppy on the boot screen and slid upwards as the disk is inserted into the drive on screen.  This only appeared on the composite out and not the RGB.

After doing some reading I saw this blog entry ( amiga-600-video-encoder-upgrade ) with someone who had also recapped his Amiga with the same issue and he suggested the cleaning fluids went up into the 221 and 222 cans and broke them.  I did pour on a LOT of cleaning agents to clean off the acid.  He used a CXA1645M to replace the original chip and some Kapton tape to isolate the 221 and 222's. There seemed to be a lot of parts that you needed to solder on to the chip with that solution to get it working, it just looked way too fiddley.

Looking further I managed to find this blog entry with a solution that suited me a little better ( https://www.ikod.se/cxa2075m ). It used just a CXA2075M and one resistor.

So I ordered some CXA2075M 's from EBay and now here we go.

** Warning **  This was a little challenging so if you don't have the equipment or skills to do it, get someone experienced to do it for you.  When you remove the CXA1145M all display outputs stop working!!

Here is the board before I started with the Original CXA1145M and the 221 and 222 cans.  You can see the effects of the corrosion of the leaky Capacitors on the legs of the chip.


Here are the new parts as per the reference blog post ( https://www.ikod.se/cxa2075m ) 



The biggest issue I had was that the blog post was for an A1200 and not an A600.  So the removal of parts to disable the 221 and 222 parts wasn't valid for me.  As I have a desoldering gun I just removed the 221 and 222 parts instead which works just as well.  I also used a hot air rework station to remove the chip.
 
When removing the 221 and 222 parts you will likely need to add solder to the pins several times to help suck all of the old solder out.  Be patient and they will come out easily.

Taking the parts off was easy, putting the new parts on was a bit soldering of a challenge.  Oh I wish I had three hands sometimes. Here is the end result, all in all I am pretty happy with it.



The old parts removed from the motherboard

As you can see both the RGB and the composite out work a treat now and no more horrible blue line!!