Shoestring

Jun 242021
 

See part 1 first.  https://www.jammarcade.net/amiga-a1200-video-repair-part-1/

 

Sockets arrived yesterday and chips arrived a day later, great timing because I’d already had the socket installed by the time the chips arrived.

I’ve decided to remove the backing on one of the sockets, I really didn’t like the idea of trying to get my soldering iron tip in between the backing and pins so I removed it. My plan was to attach some double sided tape or hot glue to the backing/shim then apply it to the MB later, I didn’t want the chip to sit so low in it’s socket in case it needs to come out later.

 

 

After lining up the pins, I had an obvious problem here. The base of the SMD capacitor at C407 in the video decoupling circuit wont allow the socket to sit flush so I decided to remove it, solder the socket in place then add the capacitor later.

 

 

Out with the old and in with the new. Socket soldered into place and connections inspected with a Microscope, then the 10uf capacitor replaced with a brand new one.

 

 

The following day later in the afternoon I received a package containing these. Who sends electro static sensitive devices in a plastic satchel ? More over the devices were clearly de-soldered/pulls yet advertised as new. Will avoid this seller in future.

 

I chose the cleanest of them all ( top right ). I then installed the plastic shim with some double sided tape to the bottom of the socket and installed the chip and tested with success.

 

I now have my blue working again.

 

 

Amiga A1200 video repair – part 1

 Computer Repair Logs, Repair Logs  Comments Off on Amiga A1200 video repair – part 1
Jun 162021
 

Whilst installing and carelessly adjusting my CF card in my A1200 with it switched on, I managed to short out some component on the motherboard via the shield which caused the machine to reboot and then come up with the following screen.

 

You can clearly see that blue is completely missing.

 

A healthy kickstart screen should look like this

I wasted no time getting to work after cursing myself for 30 minutes or so and feeling bad all night.

1st step was to figure out where the fault actually was, so I consulted the schematics to understand the design and get an idea of where to start.

I have clearly marked the important parts of the drawing by marking each of the 3 RGB colours over the signals. First of all, we have an AGA ( Advanced Graphics Architecture ) custom chip called LISA which generates the colour information internally amongst other things, this must be converted to analog via the video DAC which accepts 24 bits of colour information from LISA and then passes those analog signals directly to the 23pin D-SUB connector on the back of the A1200.

 

The same 3 RGB signals generated by the video DAC are passed to the Sony Encoder chip for composite signal and also RF out to a TV.

The issue was also reproduced on the composite out, this would confirm the encoder just gets its RGB signals from the DAC and to look elsewhere. Unlike the Amiga 600 design which uses no DAC but uses the same encoder to pass RGB to the 23pin D-SUB, the A600 video output design is similar to the video hybrid method used in the A500 for generating RGB.

 

Thankfully we have a similar problem here from RetroGameModz that I used as a reference which describes the troubleshooting process. I really liked his use of Protracker to trouble shoot the colour, this proved very useful.

 

 

In Protracker, I turned Red and Green signals to the absolute minimum and adjusted the slider for Blue and see no change at all.  So with my scope I verify the signals coming out of pins 25,26 and 26 of the video DAC.  These are labelled IOR,IOG and IOB respectively. I could see valid waveforms on both on IOG and IOR but a flat line ( low ) on IOB no matter where I positioned the blue slider in Protracker via setup from the main menu. This explains the lack of blue.

So either, the 8 bits for blue were stuck on the output of LISA or I had a bad video DAC.

I then attached my logic probe to 5v somewhere inside the machine and adjusted the slider in Protracker whilst probing R,G and B signals. To my relief my logic probe responded to each and every single one of the 24 bits coming out of LISA. So LISA was spitting out colour information but the DAC was obviously not going to deal with blue. I repeated the same measurement on IOB output of the video DAC this time with the logic probe which shows its held low regardless of the position of the slider, further confirming the lack of waveform there with the scope.

 

I wasted no time ordering some replacements.  3 x VP101-3BA manufactured by GPS/MITEL and some 44pin PLCC sockets.

So currently waiting for these to arrive from China, delivery time is 2 months.

 

 

And in preparation I couldn’t wait to remove the faulty component from the A1200.  First step was using a liberal amount of polyimide tape ( this stuff is expensive but will save you from grief ) to protect surrounding components from heat exposure, I applied some flux and then heat the chip to around 200 for 1 or 2 minutes, then raised it temp to 350 to finish off.

 

 

 

 

 

I had this cleaned up nicely. Now just waiting for the spare parts to arrive for a part 2.

 

References: Amiga 1200 Schematics.

 

Click to access A1200_R1.pdf

 

See here for part 2

 

Amiga A1200 video repair – part 2

Feb 212020
 

21/02/2020 10:59 ( AEST )

I’ve been meaning to update this page for awhile but work and life has got the better of me.

If your Track&Field/Hyper Olympic has the following layout then you have unencrypted roms and you will need this updated version of my diagnostic to run on this particular board.  Note that this version will not run on boards equipped with a K1 cpu ( 42 pin custom IC ) or a game ( usually a bootleg ) with daughterboard that has a 6809 processor onboard, the daughterboard version also has some extra logic associated with it to decrypt/unscramble the opcodes.

Note: The board does not have a K1 CPU but uses a standard 6809 processor to run the game. Decryption related circuitry is also absent from this version.

I have prepared a version that will run on this board.

 

See TEST VERSION 1.2 – Unencrypted for download

9/02/2017

TEST 1.2 is now the current version which installs in socket 5A on Konami and Centuri versions.

  • Fixed detection of ROM A7 [ $9E99 ] ( Hyper olympic bootleg) which broke in TEST 1.1

See TEST VERSION 1.2 for download

21/08/2015

TEST 1.1

This is a test release.  A BETA version will replace it and this post will be updated pending sufficient feedback. It has been reported by one tester that this version works on real hardware but more feedback is desired.

IMPORTANT: The diagnostic EPROM now installs @ 5A on the Centuri and Konami boards. For the Hyper Olympic bootleg install the EPROM @ A7 and for the NZ bootleg install @ 2A.

This frees up 4 sockets for verifying game EPROMs instead of only 3. Since 5A is mapped to 0xe000-0xffff and the reset vector is obtained at 0xfffe/0xffff, it made sense to move the test rom to this socket.

See TEST VERSION 1.1 for download

test 1.1

IMPORTANT: All versions below install in socket 1A

18/08/2015

Bullet points represent items fixed in the current version.

BETA 1.3 is current.

  • ROM A1 FOUND! text missing when generated check-sum verifies successfully in socket 3a & 4a.

TODO: Future versions will install in socket 5a. The main reason for this change is to ensure the test rom boots since the 6809 obtains the reset vector from EPROM A5 ( 0xfffe ), there is a chance that the reset vector could be corrupted if the game EPROM A5 is bad. Moving the code to run from socket 5a will prevent such an event and also make the first 4 sockets available for verifying an A5 EPROM or any others.

 

See 1.3 for download CHK: F3E9 CRC16: 1421

16/08/2015

BETA 1.2

  • Further checks suspended if video ram/colour ram is bad. Priority given to preserve NVRAM/high scores. ( worst case scenario – screen totally unreadable ).
  • Introduced audio alert. 5 beeps for bad video ram 12H, 6 beeps for bad colour ram 11H.
  • Provided work around to keep tiles on screen if scroll ram is detected as bad.

See 1.2 for download CHK: F3EB CRC16: 5695

Special thanks goes out to Purity on UKVAC for his help with testing and feedback.

1/08/2015

BETA 1.1

  • Fixed SFX menu. Speech now plays from sound index 0x80

If you believe there are missing sounds please report them in the comments.

See 1.1 for download CHK: 9909 CRC16: AB36

30/7/2015

BETA 1.0

  • Bootleg rom support added ( see hyprolymb from the MAME set )
  • Fixed watchdog reset issue during EPROM check routine
  • Fixed character bank bug ( was displaying extra bank of null tiles )
  • Added CRC of current software to version string ( calculated at runtime )

BOOTLEG – HYPER OLYMPIC ( hyprolymb )

ROM A1 $9E99
ROM A2 $35E8
ROM A4 $2FDC
ROM A5 $7DD2
ROM A7 $F932

TODO: Fix SFX test in diag mode. Speech is not playing.

See 1.0: CHK: 9F7E CRC16: 2F6F

26/07/2015

BETA 0.9

  • Support for Hyper Olympic roms added
  • MISC code improvements

See 0.9 CRC16: 70E6

0000

See below for correct 16 bit checksums matching your set.

Pre-calculated ROM Checksums.

KONAMI – TRACK & FIELD

ROM A1 $9F6E
ROM A2 $3620
ROM A3 $2FA5
ROM A4 $7CA6
ROM A5 $FEEB

CENTURI – TRACK & FIELD

ROM A1 $9DBE
ROM A2 $3CA7
ROM A3 $17C8
ROM A4 $569E
ROM A5 $E991

KONAMI – HYPER OLYMPIC

ROM A1 $9E79
ROM A2 $35E8
ROM A3 $2ECE
ROM A4 $7DD2
ROM A5 $F932

25/07/2015

BETA 0.8

  • Support for Centuri roms added.

See 0.8 CRC16: 9EBE

24/7/2015

BETA 0.7

This EPROM installs on the CPU board @ 1A. This does not replace the original software in 1A but is only used as a means of testing the main-board, sound and video.

Diagnostic mode is accessible by holding down player 2 start whilst powering the game on.

In the normal mode ( power up tests ), nvram tests may be skipped to preserve high score data if so desired. This is done via DIP 8 of SW2. A ~10 second countdown is also included even if you desire to test your nvram, in this mode nvram tests may also be skipped by pressing the “player 1 button 1”.

Power up tests also include a rom utility. This currently identifies track & field software in any of the 3 available sockets ( 2A to 4A ). For example, an A1 ROM installed in any of the above available sockets will still be identified for its designated 1A socket.

Important: A5 ROM needs to remain in socket 5A, this is because the 6809 obtains its reset vectors from this ROM. If the test rom or game fails to start and the screen is full of zeros, verify the A5 rom manually. 

Note: That this is a very BETA release and is currently in the testing phase, bugs are expected. Use at your own risk if you love those high scores.

See 0.7  CRC16: 8C8A

Apple IIe repair log – bad ram

 Computer Repair Logs, Repair Logs  Comments Off on Apple IIe repair log – bad ram
Aug 262019
 

I recently received this Apple IIe PCB from the U.S to try my luck on salvaging the 60hz IOU and using it in my International NTSC board in the hopes of getting colour which I did successfully in my previous post. This board was advertised as untested, so that normally means “DEAD” and I assumed so.

 

 

Taking one look at the RAM suggests there were issues in the past and most likely still issues. We have some original mT ( Micron ) / Apple branded DRAMs mixed in with the various replacements. Micron don’t exactly have the best reputation in regards to reliability so this is definitely a red flag. These were used by Commodore, Atari and obviously Apple as well. I guess they were cheap!

 

 

Based on the excellent condition of the board I was happy and confident in firing it up. It displays some kind of RAM error but it’s not very helpful, definitely not as helpful as the reporting in the Enhanced IIes built in diagnostic. I don’t have a choice but to go through and check each DRAM individually.

 

 

My TopMax helps me find 4 bad DRAMs of the 8. Three of which were Micron ( expected! ).

 

Dead RAM chips on the left clearly marked  to remind me that these are dead and not to be mixed up with working. These will come in useful for refining my Atari 8bit diagnostic tool.

I temporarily replaced the dead RAM chips with known good Micron pulls from my friends Atari 800xl. But I do have some NOS TMS 150ns chips that will be going in shortly.

 

Replacing the RAM confirms the fix.

 

It’s nice to have a second board ready to go if I need it, and the fact that it’s a non enhanced board with everything socketed is a plus.  I’ll be looking at converting this over to enhanced at some point via a enhancement kit which involves a 65C02 and newer roms for Apple IIc compatibility.

 

Apple IIe enhanced ( Platinum ) – NTSC 50hz to 60hz conversion

 Computer Repair Logs, Mods, Repair Logs  Comments Off on Apple IIe enhanced ( Platinum ) – NTSC 50hz to 60hz conversion
Aug 252019
 

The final revision of the exported Apple IIe and Platinums use the International NTSC PCB, this ships with a very odd 50 hz NTSC configuration. The stock motherboard is fitted with a 14.238Mhz and requires the original 50hz Apple IIe Color Monitor to display a non monochrome picture on the screen. A standard 60hz capable NTSC monitor or 50hz PAL monitor ( as expected ) fails to pickup the colour on these machines due to some odd Hybrid combination.

Unfortunately my Apple Color monitor has a dead flyback and all efforts to source a replacement or substitute part went nowhere so I had to find an alternative. One alternative is using a PAL / Color encoder card but these are rare and expensive whenever they turn up.

The theory to get colour involves changing the crystal at Y1 from 14.238Mhz to 14.31818MHz, this is logical and seems to work for most people who have tried this modification. One of the issues surrounding the crystal has already been discussed at length on the various forums, it must have an ESR of 25 ohms and not any off the shelf crystal will do apparently. Most people have had success using the specific type of crystal with the right characteristics, unfortunately I have not. After changing the crystal at Y1, I still had a black and white display on all my monitors ( Sony PVM, Philips & TEAC LCD  ) which are capable of displaying 60hz NTSC in colour.

The PVM and my Commodore 1084s PAL monitor ( Philips made ) had no issues with locking on to sync despite the black and white monochrome picture ( expected in the 1084s case ). My Philips LCD still interpreted the signal as PAL even after changing the main crystal. In fact the signal was not stable and both LCDs were struggling to lock on to sync permanently, with the picture slightly shimmering or going completely out of sync for at least half a second ( as in the TEAC’s case ).

 

This has left me scratching my head as it appears that ALL my monitors were very picky , yet other people had success.

The Technical Reference Manual, in chapter 7 states that the IOU ( input / output unit ) handles and generates the video signals, video blanking, horizontal  signals via some internal counters.

http://www.applelogic.org/files/AIIETECHREF3.pdf

There are several different versions of the IOU but information out there is rather confusing and in some cases incorrect and that’s something I’d rather not cover at all. The NTSC International and even the PAL models use a very specific version of the IOU not found in the non export, U.S versions.

  • IOU 344-0022 ( used in International NTSC 50hz and PAL models ).
  • IOU 344-0020 ( NTSC 60hz ).

I had an idea to swap out the original 344-022 IOU for the 344-0020 and I took my chance on a non tested earlier IIe PCB.  Thankfully only 4 RAM chips were bad ( mostly Micron, surprise surprise! ) which I’ll cover in my next repair log. I very carefully remove the original IOU, installed a machined pin socket and swapped the IOUs over. The original IOU still works in the other IIe after all that surgery ( Phew! ).

At some point later on I had to replace the RAM as well most likely caused by accidentally handling static prone devices without an anti-static wrist strap ( whoops! ). Not to worry, I have plenty of spares.

 

The results with splendid colour on my PVM!

 

And a valid NTSC signal on my Philips LCD ( Karateka in action! )

 

Conclusions: It was suggested the possibility that the original IOU was damaged or partially faulty ( I have to keep that in mind ) but I’ll never know unless someone else confirms the same or I can get my hands on another IOU ( 344-0022 ). I previously had the same exact issue in another IIe before I sold it, however I was using FOX143-20 branded crystals ( which have an ESR of 40 ohms ) at the time rather than the proven to work ones below which have an ESR of 25 ohms.  I still have my FOX crystals on hand, so at some point I’d like explore those again and see if colour is still possible given I’ve swapped the IOU over to the 60hz version.

 

The following crystals have been proven to work.  Still no colour on your International NTSC board  ? Try a different IOU by substitution.

ECS-143-S-1

ECS-143-S-1X.

These can be found at the link below.

https://www.digikey.com/products/en?keywords=ECS-143-S-1