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 (999)
• Amiga 4000 audio after the repair (1007)

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:

Below a short description of the repair.

Commodore PET 2001 (1977) Chiclet Keyboard (#1)

Defect:

• Garbage Screen on boot and partially in a working state.

Diagnosis/Repair:

• The Multiplexer 74LS157 (position D2) had an output (pin 4) always been in low state.

Gallery of the repair:

Commodore PET 2001 (1978) Chiclet Keyboard (#2)

Defect:

• Garbage Screen on boot.
• Memory Problems (1018 Bytes are missing)

Diagnosis/Repair:

• The garbage screen on boot was caused by a poor contact of the sockets where reside the ROMs. Temporarily fixed by inserting a precision sockets above the original socket (very bad quality sockets).
• The problem of the missing memory was fixed by replacing a RAM MPS 2114 (position J1) with a new one.

Gallery of the repair:

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:

Gotek floppy emulator with HxC firmware (Testing on Amiga Computer):

Gotek floppy emulator with HxC firmware (Testing on Amstrad CPC computer):

Gotek floppy emulator with HxC firmware (Testing on Atari ST Computer):

Gotek Audio Track Loader:

The schematics is here

Components:

• 1 x Buzzer.
• 1 x BC547 or similar bipolar transistor.
• 1 x 1k resistor.

I have to thank Jean-François DEL NERO for the support that he gave me for the bootloader programming.

source: hxc2001.com

Defect:

• The backup system not using correctly the on-board memory and don’t load any games.

Diagnosis/Repair:

• Broken pcb track under the GAL (position U9). The battery acid has corroded some pcb tracks.
• GAL (position U9) completely dead.

Note1:

• The glitches on the screen that you see in the photo are caused by a failure on my Super Famicom. I have to fix it. ;-D

Note2:

• I don’t have the .JED code of the GAL and however i have sold many years ago my PAL/GAL programmer so i cannot replace the faulty component.

Download:

• Super Wildcard 2.8CC ROM & 2 x GAL16V8 (347)
• Super Wildcard DX (EPROM & EEPROM DUMP) (469)

Explanation of how it work the program “RAM3_RAMFAIL_BAS” written by Dominic Brown in the 1990 in Super Basic for the Sinclair QL which is used to calculate what the RAM on the Sinclair QL is broken, you need to use the MINERVA ROM (RAM PassCheck).

I tried to explain how it work and i have rewrote the software in a “language” a bit more modern ;-D

MINERVA OUTPUT EXAMPLE:

——————————————
WRITE: 5 4 8 C 4 8 7 8
READ: 5 C C D 5 C C D
ADDRESS: 0 0 0 3 2 0 0 0
——————————————

HEX WRITE: 54 8C 48 78
HEX READ:  5C CD 5C CD

Convert the numbers in decimal:

DECIMAL WRITE: 84 140 72 120
DECIMAL READ:  92 205 92 205

You have to make a xor in pairs (write & read)

XOR: 84 XOR 92 = 8
XOR: 140 XOR 205 = 65
XOR: 72 XOR 92 = 20
XOR: 120 XOR 205 = 181

Now you need to do an OR with the result of the XOR starting with “0″ and continuing with the result of every OR

OR: 0 OR 8 = 8
OR: 8 OR 65 = 73
OR: 73 OR 20 = 93
OR: 93 OR 181 = 253

Convert the final result of the OR in Binary.

DECIMAL: 253
HEX: FD
BINARY: 11111101

Follow the table to find the faulty ram. Pay attention to the memory address.

1: BAD Ram
0: GOOD Ram

BINARY = 1     1     1     1     1     1     0     1

IF < $30000 (ADDRESS) = IC8  ,IC7  ,IC6  ,IC5  ,IC4  ,IC3  ,IC2  ,IC1

IF > $30000 (ADDRESS) = IC16 ,IC15 ,IC14 ,IC13 ,IC12 ,IC11 ,IC10 ,IC9

IF > $40000 Faulty ram is in expansion memory.

The Original Program (ram3_ramfail.bas) was written for the SINCLAIR QL in SUPER BASIC language by Dominic Brown (1990).
Documentation of how it work by Xad/Nightfall (2015).
Thanks to my friend for the support.

Faulty Ram Decoder Changelog:

• v0.1: First Release.
• v0.2: Added a message (Faulty ram is in expansion memory) if the Address > $40000.

Faulty Ram Decoder Online: http://www.nightfallcrew.com/minervaram

Download:

• Faulty Ram Decoder v0.1 PHP Script (984)
• Faulty Ram Decoder v0.2 PHP Script (1033)

Photo of cleaning (before and after):

To clean the power supply i have used compressed air and a media bristle brush.