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DP4 on Classic II Analog Board
- Thread starter bibilit
- Start date
I am back to troubleshooting, my TDA 4605 is only getting 5,5 volts on pin 6 instead of the expected 12 volts required to switch-on.
The Classic is hence not outputting anything.
Pin 6 is connected to the rectifier diode with only a 22k resistor in between, this was tested ok.
I am missing something ?
The Classic is hence not outputting anything.
Pin 6 is connected to the rectifier diode with only a 22k resistor in between, this was tested ok.
I am missing something ?
Problem solved on this one.
This is the late board design (220 volt), and problem was no output at all.
The Analog board is using Switch Mode Power Supply technology to supply voltage around.
So looks like this one:
The IC is expecting some information to kick the whole process (from the primary side)
The voltage expected at Pin 6 is around 12 volts (Vac), with a minimum of 11 volts, under this figure the IC (TDA 4605 in the Macintosh Classic) will be switched-Off.
When voltage is Ok, a pulse will be generated to Pin 5 which goes to the Mosfet (IRFBC 40) starting the process and producing output voltages (secondary side)
The IC is also collecting information (at pin 1) from these voltages (through the Optocoupler CNY17 or equivalent) and regulating the output (the pulse at pin 5)
My board was only suppling 5,5 volts to pin 6, far too low...
I replaced capacitor CP4 and checked diode (DP4) and resitors (RP1 and RP28) which looked ok.
But apparently the diode DP4 (1N4148) was leaky...replacing the diode kicked a very bad power supply (voltage at pin 6 was unstable, producing from 6 to 13 volts)
So in theory, regulation was in trouble also.
CNY17 was new, as well as the TDA4605... to cut a long story short, another diode was leaky (DP3 also 1N4148)
Once replaced the voltages were fine and steady, and the Classic booted right away [
]
If you are troubleshooting those units,keep in mind that voltages in the primary side are dangerous.
This is the late board design (220 volt), and problem was no output at all.
The Analog board is using Switch Mode Power Supply technology to supply voltage around.
So looks like this one:
The IC is expecting some information to kick the whole process (from the primary side)
The voltage expected at Pin 6 is around 12 volts (Vac), with a minimum of 11 volts, under this figure the IC (TDA 4605 in the Macintosh Classic) will be switched-Off.
When voltage is Ok, a pulse will be generated to Pin 5 which goes to the Mosfet (IRFBC 40) starting the process and producing output voltages (secondary side)
The IC is also collecting information (at pin 1) from these voltages (through the Optocoupler CNY17 or equivalent) and regulating the output (the pulse at pin 5)
My board was only suppling 5,5 volts to pin 6, far too low...
I replaced capacitor CP4 and checked diode (DP4) and resitors (RP1 and RP28) which looked ok.
But apparently the diode DP4 (1N4148) was leaky...replacing the diode kicked a very bad power supply (voltage at pin 6 was unstable, producing from 6 to 13 volts)
So in theory, regulation was in trouble also.
CNY17 was new, as well as the TDA4605... to cut a long story short, another diode was leaky (DP3 also 1N4148)
Once replaced the voltages were fine and steady, and the Classic booted right away [
]If you are troubleshooting those units,keep in mind that voltages in the primary side are dangerous.
Last edited by a moderator:
Those two diodes have a high failure rate.
One of my Classic was stored and i decided to play with it, only get a checkerboard display and low voltages.
As the AB was done a couple of months ago, and without testing anything else, just replaced the two diodes to get a functional unit again.
One of my Classic was stored and i decided to play with it, only get a checkerboard display and low voltages.
As the AB was done a couple of months ago, and without testing anything else, just replaced the two diodes to get a functional unit again.
still having some troubles with those Classic Analog Boards.
One has a very unstable 5 volt output, while the 12 volt seems ok (screen is also unstable)
of course, i gave replaced all capacitors, opto, TDA and diodes but this is giving me headaches.
Can a MBR1045 diode be leaky ? i can increase the voltage but i will increase at the same time the 12 volt output, creating other troubles.
One has a very unstable 5 volt output, while the 12 volt seems ok (screen is also unstable)
of course, i gave replaced all capacitors, opto, TDA and diodes but this is giving me headaches.
Can a MBR1045 diode be leaky ? i can increase the voltage but i will increase at the same time the 12 volt output, creating other troubles.
I have the same problem with Classic II AB. What could it be? I'll try to replace DP4 and DP3 diodes
