Hello everyone,
At the start of the week i recently acquired a RGB modded Super CD-Rom2 along with a PCE from France but the whole thing has turned into a nightmare to be honest. The guy i purchased it from did not inform me of the type of mod inside the SCD2 and its now developed a fault. To be fair the guy is clued up on mods and the PCE and is trying to help me get the SCD2 back up and running.
I have put together everything from the start and what i have discovered, here goes.
Upon powering on the SCD2 with the PCE connected resulted in no image on the TV. Further known working RGB scart cables and AV lead were tested from the SCD2 Din 8 out but resulted in no image. The supplied RGB scart cable was tested on a known RGB modified Core Grafx II and resulted in no image. Further checks were carried out and the following below was found.
The SCD2 External 12v PSU was measured and verified. 10v Power out of the SCD2 was measured and checked ok. Connecting a working RGB Core Grafx II to the SCD2 with a working RGB scart cable from the Core Grafx II Din 8 provides an image to the TV whilst running HuCards only. Upon switching on the Core Grafx II with no HuCard inserted results in no image (the Super CD Bios screen should be displayed)
Upon opening the SCD2 and carrying out visual checks there is no apparent obvious issues. The RGB mod can be seen to run from the PCE bus connector to the Din 8 on the SCD2.
Whilst measuring voltages internal to the SCD2 whilst switch on, the following was seen. the 12v input is healthy from the input DC jack and across both sides of the Diode. The 12v is also passed over to a B744 PNP Transistor, 12v to ground is measured into the Emitter on the Transistor. There is 3v measured to ground from the Base of the Transistor. It is expected that 12v should be seen on the Base and after switching on the PCE and 12v should be seen on the Transistor collector.
Whilst powering on the PCE the PNP Transistor effectively works as a switch, and a voltage is output on the Transistors Collector. The Collectors voltage is supplied to the Voltage Regulator (type 7805) and input voltage is regulated down to 5v and supplied to SCD2 circuits.
Whilst measuring voltage at the Input of the Voltage Regulator 3v was seen. The input is to low for the voltage regulator to function (7805 requires 7.5v to operate)
Further cheks were carried out and nothing obvious was seen other than the fact that the voltage on the Transistor Base and Collector output to the Voltage Regulator is far to low. It is expected that the B744 PNP Transistor is faulty.
The Transistor is removed from the board and tested using the Diode test funtion on a multimeter. It is found that there is a short circuit between the Base and Collector of the Transistor. The deivce is confirmed to be faulty and replacement B744 PNP's are ordered.
Further checks were carried out to see what could have caused the SCD2 Transistor to fail and the following was seen,
There is a wire link from the SCD2 Din 8 (pin2) to the Input supply of the 7805 Voltage Regulator. This is supplying 12v to this Pin. Further information from the seller states that this mod was common in France to allow for TV switching for RGB or for the TV to switch to the AV input automatically. Originally Pin 2 on the SCD2 Din (and PCE's) was a ground connection.
burogu.makotoworkshop.org/index.php?post/2012/03/04/rgb-pce
It is expected that the RGB cables, AV cable may have caused an issue. Upon further checks it was verified that when the AV Cable is plugged into the SCD2 Din 8 Pin 2 (originally ground) and Pin 3 (sync & video) are connected.
From the above it is now clear that when the PCE is switched on with the AV Cable connected the 12v link from the Input of the Voltage regulator was shorted to ground. It is expected that this has caused the Transistor feeding the 12v input to the regulator to fail.
Further components in the Power circuit may still have been affected by the short circuit to ground although everything appears to be ok. Nothing can be verified until a replacement Transistor is fitted and the correct voltage is applied to the 7805 regulator input. All other Input voltage measurements to the Transistors Emitter are correct.
The seller confirms that he has used an AV cable before on a SCD2 with this mod on his machine and that it had previously blown the external PSU fuse. On this occasion the fuse did not blow on the PSU unfortunately.
I am hoping that the replacement Transistor at least functions supplying the 7805 with the correct input voltage and further checks can then be carried out. I am hoping the Transistor arrives tomorrow or Saturday. If anyone can provide any input or advice it would be very much appreciated.
Cheers
Scott
At the start of the week i recently acquired a RGB modded Super CD-Rom2 along with a PCE from France but the whole thing has turned into a nightmare to be honest. The guy i purchased it from did not inform me of the type of mod inside the SCD2 and its now developed a fault. To be fair the guy is clued up on mods and the PCE and is trying to help me get the SCD2 back up and running.
I have put together everything from the start and what i have discovered, here goes.
Upon powering on the SCD2 with the PCE connected resulted in no image on the TV. Further known working RGB scart cables and AV lead were tested from the SCD2 Din 8 out but resulted in no image. The supplied RGB scart cable was tested on a known RGB modified Core Grafx II and resulted in no image. Further checks were carried out and the following below was found.
The SCD2 External 12v PSU was measured and verified. 10v Power out of the SCD2 was measured and checked ok. Connecting a working RGB Core Grafx II to the SCD2 with a working RGB scart cable from the Core Grafx II Din 8 provides an image to the TV whilst running HuCards only. Upon switching on the Core Grafx II with no HuCard inserted results in no image (the Super CD Bios screen should be displayed)
Upon opening the SCD2 and carrying out visual checks there is no apparent obvious issues. The RGB mod can be seen to run from the PCE bus connector to the Din 8 on the SCD2.
Whilst measuring voltages internal to the SCD2 whilst switch on, the following was seen. the 12v input is healthy from the input DC jack and across both sides of the Diode. The 12v is also passed over to a B744 PNP Transistor, 12v to ground is measured into the Emitter on the Transistor. There is 3v measured to ground from the Base of the Transistor. It is expected that 12v should be seen on the Base and after switching on the PCE and 12v should be seen on the Transistor collector.
Whilst powering on the PCE the PNP Transistor effectively works as a switch, and a voltage is output on the Transistors Collector. The Collectors voltage is supplied to the Voltage Regulator (type 7805) and input voltage is regulated down to 5v and supplied to SCD2 circuits.
Whilst measuring voltage at the Input of the Voltage Regulator 3v was seen. The input is to low for the voltage regulator to function (7805 requires 7.5v to operate)
Further cheks were carried out and nothing obvious was seen other than the fact that the voltage on the Transistor Base and Collector output to the Voltage Regulator is far to low. It is expected that the B744 PNP Transistor is faulty.
The Transistor is removed from the board and tested using the Diode test funtion on a multimeter. It is found that there is a short circuit between the Base and Collector of the Transistor. The deivce is confirmed to be faulty and replacement B744 PNP's are ordered.
Further checks were carried out to see what could have caused the SCD2 Transistor to fail and the following was seen,
There is a wire link from the SCD2 Din 8 (pin2) to the Input supply of the 7805 Voltage Regulator. This is supplying 12v to this Pin. Further information from the seller states that this mod was common in France to allow for TV switching for RGB or for the TV to switch to the AV input automatically. Originally Pin 2 on the SCD2 Din (and PCE's) was a ground connection.
burogu.makotoworkshop.org/index.php?post/2012/03/04/rgb-pce
It is expected that the RGB cables, AV cable may have caused an issue. Upon further checks it was verified that when the AV Cable is plugged into the SCD2 Din 8 Pin 2 (originally ground) and Pin 3 (sync & video) are connected.
From the above it is now clear that when the PCE is switched on with the AV Cable connected the 12v link from the Input of the Voltage regulator was shorted to ground. It is expected that this has caused the Transistor feeding the 12v input to the regulator to fail.
Further components in the Power circuit may still have been affected by the short circuit to ground although everything appears to be ok. Nothing can be verified until a replacement Transistor is fitted and the correct voltage is applied to the 7805 regulator input. All other Input voltage measurements to the Transistors Emitter are correct.
The seller confirms that he has used an AV cable before on a SCD2 with this mod on his machine and that it had previously blown the external PSU fuse. On this occasion the fuse did not blow on the PSU unfortunately.
I am hoping that the replacement Transistor at least functions supplying the 7805 with the correct input voltage and further checks can then be carried out. I am hoping the Transistor arrives tomorrow or Saturday. If anyone can provide any input or advice it would be very much appreciated.
Cheers
Scott
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