Repair Motherboard (ASSY 326298) Drean Commodore 64

Defect:

• Black Screen.
• Missing Video Signal.

Cause of the Missing Video Signal:

• The motherboard of this C64 to work with the PAL-N video (Argentina) has been modified. Some pcb tracks are cut off and the modulator has been replaced. There are also a few bridges to retrieve the S-VIDEO output (luma / chroma).

Video Restoration:

• I have made a bridge with a wire for recover the composite signal that has been removed (tiny blue wire).

Repair:

• The cause of the black screen are 2 x MK 4564 ram in short circuit.

Photo gallery of repair:

The Commodore 2031 and Commodore 4031 are single-unit 5¼” floppy disk drives for Commodore International computers. They use a similar steel case form to the Commodore 9060/9090 hard disk drives, and use the IEEE-488 interface common to Commodore PET/CBM computers. Essentially, both models are a single-drive version of the Commodore 4040.

The Commodore 2031LP is functionally the same as the 2031, but used the lower-profile tan case of the second version of the Commodore 1541 floppy disk drive intended for home computer use.

These drive models use a single-density, single-side floppy data storage format similar to that used by the Commodore 1540 & Commodore 1541 drives, but with a slightly different data marker indicating which model originally formatted the disk. The low-level disk format is similar enough to allow reading between models, but different enough that one series of drive models cannot reliably write to disks formatted with one of the other model series. A different of one extra ‘header’ byte is what causes this write incompatibility.

Gallery:

Repair/Restoration Commodore Floppy Drive 2031LP

Defect:

• Lock lever of the Floppy Drive broken.
• When the Floppy Drive is powered up, red LED stays on and spindle motor runs continuously.

Repair/Restoration:

• Replaced the Lock lever with a new one taken from a Commodore Floppy Drive 1541 (spare parts)
• Replaced the ROM (UAB5 901484-05) with a EPROM MCM 68766 supplied from my friend Giacomo Vernoni.

Note:

The Eprom programming was done with a EPROM programmer Promenade by Jason-Ranheim Co. for Commodore 64.

Repair/Restoration Gallery:

Download: Commodore Floppy Drive 2031LP/HP Rom (1201)

source: wikipedia

The Home Computer Asem AM 100 is a clone of the Apple II+ (Apple // Plus). This computer was manufactured and assembled by ASEM S.p.A. Artegna (UD) / Italy.

The AM 100 is fully compatible with all the software available for the Apple II and II+. I have personally tested many programs and i’ve never found problems of compatibility.

Unfortunately this computer is arrived faulty, the repair was more simple than i expected, thanks to the IC sockets located on the computer motherboard.

Works that have been made:

• Replacing IC 74LS161 which shows a vertical band on the screen.
• Removing RIFA filter capacitor located inside the PSU.
• 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
• General cleaning of the case outside/inside, monitor and keyboard.
• EPROM dump.

All these works are documented with photos that you can find below.

Gallery repairs:

12►

Under the cover gallery:

12►

Final photos:

Interesting discovery:

Inside the Floppy Drive reader (Apple clone) i have found the same mechanics (Mistumi / Newtronics) of the Commodore Floppy Drive 1541. See the first three pictures of the gallery: Under the cover.

Download: ASEM AM 100 full Eprom Dump (1207)

Jean-François DEL NERO (who’s behind the HxC SD Floppy Emulator) recently has released a version of the HxC emulator firmware that is compatible with the STM32 chip used in the Gotek floppy emulators.

This means that the great functionality of the HxC SD emulator is now available on cheaper and more widely available hardware.

The bootloader to convert the Gotek floppy drive in HxC compatible must be purchased on the website HXC 2001 by sending an email to Jean-François DEL NERO. The price of the bootloader is one-off 10 Euro per Gotek that you want to update. Future updates of the software are free and can be made from a USB stick

The HXC Usb (Gotek) firmware supports:

Flashing the Gotek floppy emulator with HxC firmware:

source: hxc2001.com

Replacing electrolytic capacitors Commodore Amiga 1200.

As you can see from the photos, the latest motherboard (Gallery full Recap Amiga 1200 #3) of Amiga 1200 suffered the classic problem of leaking capacitors.

Gallery full Recap Amiga 1200 #1:

Gallery full Recap Amiga 1200 #2:

Gallery full Recap Amiga 1200 #3:

Amiga 4000 badly Distorted Clipped Saturated audio Repair.

The problem is quite simple to find. You have to make some measurements on the integrated SMD LF347 (Op AMP) with the computer running and no sound.

You need to measuring pin 1 and pin 7 and should have a voltage of about 2.5V if the voltage as in my case (see photo) is  of 11.43v and 11.37v. Something is not working.

At this point you must also perform a new measurement on the pin 14 and pin 8, if also in this case it has a higher voltage of 2.5v evidently there is’ something that doesn’t work or with the LF347 or with the 750ohm resistor (R440 and R430).

The other three measurements to be done are the two input voltages, pin 4 should be about 12V and -12V on pin 11 approximately. In my case (see picture) are + 12.28v and -12.04v and are fine.

The third measurement is the Voltage Reference (Vref), this is very important, should not be less than 2v or greater than 3v. In my case (see photo) was 5.30v. This problem could be caused either by the circuit that provides the VRef (2 resistors and two capacitors) or just the same ic that creates problems with the Vref input.

In my case the failure was caused of the integrated SMD LF347 that i have replaced with a LM324. After replacing the voltages are back to normal, in the example photo you can see the Vref at 2.33v

The Amiga sound now works very well.

I have repaired several Commodore Amiga 4000 with the LF347 burned and from my personal experience can say that the acid leakage of capacitors C404, C433 and C443 make some short circuits on pins of the LF347 that obviously dies.

Audio before and after the repair:

• Amiga 4000 audio before the repair (1059)
• Amiga 4000 audio after the repair (1071)

Gallery:

Nothing of easier to put a socket for the oscillator to allow overclocking.

Gallery:

Yet another Commodore 64 repaired

Defect:

• White Flashing Screen then Black Screen.

Replace parts:

• 2 x 74LS257
• 1 x 6569 VIC-II

Note:

• After replacing the VIC-II (6569) the screen has stopped flashing but there was still some component broken.

I did this repair for a friend of mine after i heard that the new power supply cost 89.00 Euros !!

I have inserted a female RCA connector thus avoiding that the problem of “broken” cable happen again.

Gallery:

After the explosion of the filter capacitor (see video) i have removed the charred component.

Gallery:

Video:

The original Famicom (Japanese Nintendo) consoles are superior in design compared to the American/European NES.

One long forgotten feature is the extra sound channel, this extra channel was disconnected on US/EU console and removed from US/EU games. Castlevania 3 is a classic example. The original Japanese version has a much different theme song.

Below the photos of the fix to get the extra channel on the US/EU consoles.

Gallery:

source: krikzz.com

I have received two Computer Apricot F1e without accessories and aesthetically destroyed so i have decided to recover all that was possible.

This gallery shows some stages of the repairing of the Floppy Drives of the Commodore SFD-1001 & Commodore CBM 8296D.

Defects found on the Floppy Drives:

• Floppy drives had the capacitors that leaked acid on the motor control pcb.

The difficulty was rebuild the tracks of the pcb and remove the most of the leaked acid of the capacitors. Unfortunately on the aesthetic level this type of repair are not perfect, but i’m glad that all drives now work.

To test the correct operation of the Floppy Drives i have used a working SFD-1001 with a ZoomFloppy Interface through the IEEE-488.

Replacing bad capacitors (Floppy Drive #1):

Replacing bad capacitors (Floppy Drive #2):

Replacing bad capacitors (Floppy Drive #3):

The reason of the replacement is the leaky capacitor.

The Aluminum Electrolytic Capacitors (SMD) used in these machines eventually exude their conductive contents onto the mainboard causing short circuits and corrosion of the pcb tracks.

Replacing the capacitors on an Apple Macintosh Classic II:

As you can see from the first photo i had to replace the cathode ray tube (CRT) of a Macintosh SE/30 because has a “ghost image”.

The replacement is very simple but you have to replace also the deflection yoke because the yoke connector is different between Classic and SE/30.

The replacement of the deflection yoke obviously also involves the calibration of the image. The calibration of the image is not  simple and should be done with the computer on. Be careful there are very high voltages on the cathode ray tube (CRT).

Gallery of the replacement: