This is a little description of the repair of a Radio Shack TRS-80 Model 1 for a Friend.

The computer comes with several problems.

• Some IC are dead or in shorted state.
• Keyboard flat cable.
• One key “L” is dead.

Finding the cause of the fault has not been easy, i had to ask for a help to Ian, this dude is an expert of TRS-80 repairs.

How you can see from the photos, i had to replace a number of IC.

• 4 x Video RAM 2102 (Z62 / Z63 / Z46 / Z48)
• 1 x Z80 (Z40)
• 1 X 74LS157 (Z31)
• 1 X 74LS93 (Z32)

Stage of the defect (before and after):

Keyboard repair (replacement of internal contacts):

Micro Computer Technical Reference Handbook:

Download: TRS-80 Micro Computer Technical Reference Handbook (2493)

This is the story of a Commodore CBM (PET) 3032 recovered in a pitiful state.

The motherboard was covered of rust and many IC are in short circuit. I had to replace some IC (broken or full of rust), rebuild some paths of the pcb and clean very well.

I have also restored the inside of the case, using an anti-rust gel painting.

Photos and Description of the work made:

Read more…

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This is a Video RGB Hack for the console Sega SG-1000 II (Mark 2).

The Sega 315-5066 Video Chip inside the Sega SG-1000 II (Mark 2) used in the latest version of the console uses two video output formats: NTSC Composite video (converted to RF), and RGB (not connected).

The RGB Video is the stuff from which all other formats are born. Once your RGB is tapped it can be easily converted to Component or S-video, giving stunning output far superior to what the Sega SG-1000 II natively offers (only RF).

There are several caveats, of course. The biggest is the quality of the RGB output – it’s not very bright, and will result in an image without much contrast, so you will probably need to add an amplifier. Even on monitors that display a very good image without the amp you’ll sometimes find the sync signal needs an amp to generate a stable image.

I have used the same RGB/Sync Amplifier used on the PC-Engine, components and the Original schematic are shown below.

Schematic:

Components:

• 4 x 2SC1815 (Transistor)
• 4 x 220 μF 16v (Electrolytic capacitor)
• 4 x 10 μF 16v (Electrolytic capacitor)
• 4 x 75 Ω (Resistor)
• 8 x 10 KΩ (Resistor)
• 1 x 300 Ω (Resistor)

The three photos below show the connection between the RGB Amplifier and the PCB of the Sega SG-1000 II.

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I have found a Kaypro 4/84 in a non working state and some days ago i have decided to open it and i have realized that some components of the power supply are exploded and the video pcb was cracked.

I have not repaired the power supply because some components like the two burned transistors (Motorola W30 and V30) are not on the market, if you have more information about these components please leave me a message.

I had to fix the video pcb and i have installed a 200w Slim ATX power supply inside the Kaypro. I have made also other improvements to the computer, replaced the battery, totally exhausted and installing the KayPlus rom that offers some enhancements to this computer.

Below you can find the image of the Floppy Disk CP/M 2.2F 62k patched + Tools KayPlus in IMD format (ImageDisk) for the Kaypro 4/84.

Download: Kaypro 4/84 CP/M 2.2F 62k + Tools KayPlus (1488)

My Work Bench for small electronic Repair.

I am very happy to have repaired for my friend four PCB Commodore in one and half hour.

The defects are:

• Motherboard Commodore 64 ASSY 250466 with IEC bus broken. (replaced ic 7406 – U8)
• Motherboard Commodore 64 ASSY 250407 with a Video Output problem with some programs, like FIBR File Manager. (replaced ic 6526 – U2)
• Motherboard Commodore 64 ASSY 250425 with strange character at startup. (replaced ic 4264 – U12)
• Motherboard Commodore Floppy 1541 ASSY 1540050 REV C with IEC bus broken. (replaced ic 7406 – UB1 and ic 7414 – UA1)

I have recovered a Osborn 1 in pretty nice cosmetic conditions but broken ;-(

List of broken stuff:

• Startup Garbage screen.
• Long startup beep.
• Reset works 1 times out of 20.
• Modem port desoldered.
• Powersupply ripple.
• Some screws missing.

Solutions & Fixes:

• Powersupply Ripples: Replaced some capacitors.
• Modem Port de-soldered: Fixed the cold solder.
• Startup garbage screen/long beep/reset: I have replaced a broken 4116 RAM.
• Screws missing: Replaced with a new one.

I have to thank Terry ‘Tezza’ of Classic Computers Blog for the piggyback ram guide.

I used an oscilloscope to find the faulty ram cause all ram in my motherboard seemed to work well. In the photo #9 you can see the signal of the pin 2 (data in) of a faulty ram, while in the photo #8 the same signal of a working a ram.

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Macintosh SE/30 Fixing Motherboard Faults.

I spent many months (eight) to repair some of these macintosh SE/30 motherboard, like you can see in the gallery.

The flaws that i could find and repair are:

• Some multiplexers (74F253 or like) burned.
• Some Video Ram burned.
• Very Dirty Motherboard.
• Electrolytic capacitors have to be replaced.
• Reseat the RAM and ROM SIMM.
• Some track of the PCB broken or corroded by the acid.
• Replaced the lithium battery with a new one.
• Cold solder joint on chip: RP4/RP5/RP6 – UI2/UI3/UI4 – UJ2/UJ3/UJ4

The flaw that you see in the first picture and that should be the “Jail Bar Pattern” or “Smile Mac in Jail”, in this case is not been so. For this reason i spent a long time to find the fault.

However, i recovered 3 motherboards and I consider myself quite satisfied.

source: Repair Macintosh SE/30 68kmla.org #1 68kmla.org #2