Commodore Amiga 2000 PSU Upgrade.

I have replaced the PCB of the Commodore Amiga 2000 power supply because tired and died after many years of use and there was not the slightest sense of the repair.

The difficulty to the present day is finding a power supply ATX v1.0 with -5v (white wire) in the later versions of ATX PSU was removed, the Amiga 2000 uses this voltage for the ZORRO cards.

*UPDATE*

If you have trouble to finding an ATX power supply with the -5v output (white wire on the connector) you could use a voltage regulator LM 7905 to adjust the voltage from -12v (available in all ATX power supplies also of the latest generation) to -5v.

Due to the missing TICK signal you need to move the jumper J300 to the position 2-3 and if you have an Amiga 2000 REV4x you need to move the jumper J34 to the position 2-3.

Below the work was done.

Gallery:

12►

source: John “Chucky” Hertell Blog

Some months ago i have decided to upgrade the power supply of my Commodore Amiga 4000 with a good ATX power supply, compact and with a high amperage.

I have found the SFX POWER 2 300w from the German Company: Be Quiet. The power supply is perfectly suited to my needs.

Below the work was done, anything of complex if not fit the PCB inside the power supply of the Commodore Amiga 4000.

Gallery:

Easy trick to improve a little bit the video quality for the Commodore 64.

The fix can be made without removing the modulator. Obviously the RF output doesn’t work anymore.

Gallery:

Hex file for upgrade/mod the Vogatek A51099 Arcade Supergun 16F505 controller chips by MCJ Design 2007

Installation instruction:

• Simply program the hex file onto 2 * Microchip PIC16F505 chips.

Features:

• Press “A” on Megadrive/Genisis controller on the first power-up (this fixes random key outputs if the 2nd Controller is not used).
• PCB mod (detailed photo in the archive). Press Start + C to add coin/credit.

Gallery of the firmware upgrade:

Download: Hex file for upgrade/mod the Vogatek A51099 (926)

Repair Sinclair Spectrum +3 Power Supply

Defect:

• Dead.

Problems:

• All pad of the transformer output are broken.
• Broke the fuse holder and therefore the fuse it moves inside the power supply.

Repair:

• I have made bridges to restore the connection between the pcb and the transformer.
• Replaced the fuse holder.

Gallery of the repair:

Someone has to do this tedious job and also i advise you do not postpone the capacitors replacement.

Macintosh Recap:

• 1 x Macintosh Portable
• 1 x Macintosh SE (battery removed)
• 1 x Macintosh LC520
• 1 x Macintosh Color Classic

Gallery of the Macintosh Recap:

Repairing Radio Shack TRS-80 Model 1 ..for the third time

Defect:

• SHIFT keyboard switch broken.
• Garbage Screen on boot (already repaired).
• Flat cable of the Keyboard broken (already repaired)

Repair:

• Replaced the keyboard switch with a new one taken from a keyboard (the good one) of the Texas Instruments TI-99/4A that helps me many times.
• Replaced a 2102 Video SRAM.
• Rebuilt the keyboard flat cable.

Gallery of he repair:

Jungle King Coin-op – Taito Original – Insert Coins Workaround-Fix

Defect:

• The game works only in Demo mode because doesn’t work the insert coins switch.

Solution:

• I followed a guide that i have found online where recommend to cut the pins 3-4-9-10 of the IC 74LS08 (IC28) which is just below the little ROM PCB (no bootleg). This problem or bug is present on both version, original or bootleg of Jungle King.

Gallery:

source: wiki.aussiearcade.com.au

Batch of repairs in one week (report):

• 1 x Amiga 500 (Green screen of death – Replaced 4 x DRAM)
• 1 x Amiga 500+ (Leaked battery acid – Cleaning / Replaced GARY socket)
• 1 x Amiga 600 (Distorted Clipped Saturated audio – Replaced LF347 / Total Recap / Cleaning)
• 2 x Amiga 600 (Total Recap / Cleaning)
• 2 x Amiga 1200 (Total Recap / Cleaning)
• 1 x Texas Instruments PHA-2037 (Missing Pb Component Video Signal – Replaced LM318)

The problem is quite simple to find. You have to make some measurements on the LF347 (Op AMP) with the computer running and without sound.

You have to measuring pin 1 and pin 7 and should have a voltage of about 2.5V if the voltage as in my case is of 11.30v and 11.37v. Something is not working.

After replacing the LF347 with a LM324 or better a TL084 the right voltages are back and the sound works again.

Gallery of the repair:

*UPDATE*

After a couple of days, i have realized that the Amiga 600 still had some problems with the sound, although subtle but annoying and after a few measurements i have concluded that the LM324 is not fully compatible and cannot replace the LF324 (at least on the Amiga 600/1200).

After removing the LM324 and replaced with a TL084 everything has started to work much better than before.

I have done an accurate cleaning of the leaked battery acid on the mainboard.

I have also replaced the GARY socket destroyed by battery acid and rebuild a pcb track with a wire.

Gallery of the repair:

The problem of the green screen of death is usually due to a problem of DRAM,FAT AGNUS (chip or socket), GARY.

In this case all four DRAMs are failed. The pin 18 (IO/3) was always at high level.

Replacing DRAM everything has started to work properly.

Gallery of the repair:

We begin to explain what is this PHA-2037. This interface/Converter for the Home Computer Texas Instruments TI-99/4a is used to convert the video signals from Component (Y/Pb/Pr) to RGB (Scart Standard).

The defect of the PHA-2037 that i have received for repairing is to display images without the “BLUE” color in this case of the Video Component “Pb”.

The problem was in one of the three LM 318 (Op Amp). Just replaced, the PHA-2037 has begun to work properly.

PS: How you can see from a photo a pin of a transistor has not been cut. Maybe it was better to do it. :D

Gallery of the repair:

Brief summary of NOT repairing the Commodore Chessmate of a dear friend (Giacomo Vernoni).

The Chessmate I received had a funny defect: it worked for 10-15 seconds and then freezed completely with harrowing sounds in the background. So the defect appeared when something warmed up.

Having another Chessmate (mine) to compare the signals to, I noted right away that communication was missing between RIOT (6530) -> ROM (6332) -> CPU (6504) -> RAM (AM9111); CLOCK and RESET were working fine.

I sprayed synthetic ice on the 6530 RIOT to check if the problem was caused by this IC: as a matter of fact, after lowering its temperature, the Chessmate began to work again. I was glad I found the problem, but quite unhappy because the spare part is almost impossible to find. To double check I decided to unsolder the 6530, install a socket, and try it on my Chessmate.

It worked! Damn… after thinking about it for a while, I thought that maybe the spray partially freezed the nearby ROM too.

So I reinstalled the 6530 back in the non-working Chessmate, I turned it on, and after 15 seconds I sprayed the synthetic ice on the 6332, and it magically worked again.

That’s it… from that moment on, the Chessmate always worked! after the freezeing spray I left the Chessmate turned on for two hours and it never stopped working.

So, I’m asking myself: did the ice repair the ROM? Will it die again? probably yes :-D Maybe there was some small tin residue on the PCB that I removed by spraying it: I noticed that the Chessmate had already been repaired before, there were visible signs on the pcb.

It will remain a mystery, anyway the MPS 6322 ROM can be replaced by a 2532 EPROM (pinout compatible) or by a 2732 EPROM with an adapter.

Gallery:

Regeneration of the Keyboard PAD.

Some keys did not work properly. The Keyboard PAD have been regenerated using a suitable product that can be found for sale on eBay. Try: KEYPAD FIX

Gallery of the fix: