The motherboard conditions are not good, very badly. All capacitors have released acid, some are gone and the same for other components like the transistor Q233 2N3904 SMD amplifying for the video signal BLUE RGB. The Decoder U12 CXA1145 Sony has the pins eaten by the acid of the capacitors.

Poor Amiga …

Work to do:

• Solder resistance from E232R that is disconnected because the acid of the capacitors has leaked and corroded..
• Solder the transistor Q233 that is disconnected because the acid of the capacitors has leaked and corroded.
• Rebuilding a dozen pf pcb track between the IC U12 and the rest of the PCB and rebuilding also the through holes of the PCB.
• Replacing electrolytic capacitors, probably due to the state of the pitches i don’t use SMD capacitors.
• Replacing the male Harddisk connector some legs are broken at the base because the acid of the capacitors has leaked and corroded.

Gallery of the repair & cleaning:

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I start to saying that this type of repair should NOT be made, are not good although the repair can succeed, these damaged motherboards are good for spare parts.

It took me 10 hours to repair and if i ask 15,00 euro per hour like a housekeeper, would be 150,00 euro excluding components and cleaning case … but who pays 150,00+ euro ? no one in the world. :-D

This is one of the reasons because do not exist anymore electronic repairs or there are very few people can do it, nobody is willing to pay.

Works that have been made:

Foreword almost all pcb pads are leaked of the acid, although i have cleaned more times so as not to heat the electrolyte liquid that is worsening the situation, unfortunately the pcb pad could not resist to a new solder and they are broken.

• Soldered the E232R resistor, it’s no a good soldering because the pad are in a badly state but working.
• Soldered a transistors Q233 (2N3904) not SMD, the pitches are gone when i have tried to solder the SMD version.
• Rebuilt 10 x connections doing a horrible jumpers in bizarre places.
• Replaced the electrolytic capacitors.
• Replaced the male connector for the Harddisk.

It’s a shit … but it works!

Commodore Amiga 600 Gallery (Before & After):

Yet another Commodore 64 (USA-NTSC) repaired.

Defect:

• Garbage screen / Black screen.

Repair:

• Replaced 1 x PLA 906114
• Replaced 1 x MOS 7708 (74LS257)

Note:

• The first time the Garbage Screen was in Black & White and then after replacing the PLA 906114 a new Garbage Screen is back with some colors :-D (see photo)

Gallery of the repair:

Texas Instruments TI-99/4A Repair (#1)

Defect:

• Wave/Raster Lines.

Replaced parts:

• 1 x Variable Inductor 2 -> 4.5 μH (L100).

Gallery of repair:

Texas Instruments TI-99/4A Repair (#2)

I should point out that someone has already tried to repair, without success.

Defects:

• Black Screen (no raster, no sync) short circuit between 12v and 5v . . . and then . . .
• Wave/Raster Lines.
• Blue Screen with tiny Vertical lines and deafening sound.
• Garbage Screen.

Short Circuit Note:

• The short circuit was due to a malfunction of the IC: TIM9904ANL (U601)

Replaced parts:

• 1 x Variable Inductor 2 -> 4.5 μH (L100).
• 1 x TIM9904ANL (U601)
• 2 x MCM 6810P RAM 128×8 (U608 – U609)
• 1 x 74LS245 (U614)
• 1 x TMS9929 (U100)

Gallery of the repair:

Commodore PET 2001 Chiclet (1978) Fixed.

Defect:

• Garbage screen.

Repair:

The problem of this computer was caused by the oxide on all pins of the RAM and inside of the sockets as you can see from the photos.

To clean the pins of the IC i always use the same way, gently with a rasp nail on the ic pins and then spray a bit of air, see photo.

For cleaning the socket i scraping with a fine tip gently the contact inside the socket.

I have tested all with the ROM/RAM board and simulating the various BASIC and configurations of RAM and loaded some software, including my demo with the PET MicroSD by Dave Curran (Tynemouth Software)

Everything worked perfectly.

As you can see from the photos i have now a complete workstation for repair PET 2001 out of the box, avoiding to have on the table the computer that takes a lot of space.

Gallery of the repair:

Grundy Newbrain repaired

Defect:

• Dead.

Analysis:

• The acid of the capacitors has corroded some pcb tracks and pitches of the main pcb.
• One of the two flat cable (main pcb -> keyboard/vfd pcb) previously repaired cause short circuits and doesn’t work.
• Removing the Filter capacitor “RIFA” in the external PSU (removal made 7 months ago)

Repair # 1:

• Replaced all the electrolytic capacitors.
• Rebuild the PCB tracks corroded by the acid of the capacitors.
• Replaced the flat between the main PCB and the keyboard/vfd pcb.

The computer now turns on but the VFD (Vacuum Fluorescent Display) displays weird characters and the composite video signal is dead.

Repair # 2:

I have used a Z80 NOP generator that i have made some years ago for repairing ZX Spectrum/Sinclair and that causes the Z80 to process only “NOP” instructions
and consequently on the address lines we can see with a oscilloscope a perfect square wave.

With this simple “trick” i have immediately found the faulty component that break one of the address lines of the CPU (A1). The exact same fault was found by Thomas Gutmeier.

• Replaced 1 x 74LS257 (IC 412)

The computer now works perfectly.

Gallery of the repair:

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Download: Grundy NewBrain Schematics (1326)

Zenith Data Systems (ZDS) was a division of Zenith Electronics founded in 1979 after Zenith acquired Heathkit, which had, in 1977, entered the personal computer market.

Headquartered in Benton Harbor, Michigan, Zenith sold personal computers under both the Heath/Zenith and Zenith Data Systems names.

Gallery:

Laboratory Bench Transformer for repair Commodore CBM/PET series 2001/30xx/40xx(not fat – 8032 motherboard)

Transformer Output Pinout:

• PIN: 4 – 6 = ~16VAC
• PIN: 4 – 5 = ~8VAC
• PIN: 5 – 6 = ~8VAC
• PIN: 7 – 8 = ~16VAC
• PIN: 9 – 10 = ~16VAC

Input:

• 110v

Gallery:

Thanks to Andrea Pierdomenico for this great donation made some years ago.