PlayStation 2
Modbo v5.0 - No display - Part 4
July 22, 2023
Resistor Redemption: Unmasking the Modchip Mayhem
Ok, so in the last post, the 5V rail theory didn't pan out. Where to now? Time to go back to basics and try and think this through again. When the console is powered on it shows a black screen. There is also no audio, so looking at the block diagram and tracing backwards from the output stages, what is a common component which could result in no video, and no audio?
The IOP and the BOOTROM ICs seemed to be possible culprits. Both are early in the boot chain, and presumably if they were not functioning properly the system would be in a sort of dead-end state. The CPU is of course another possibility, but the BGA package was going to be hard to probe many of the interesting pins. It was my understanding from researching that the BOOTROM IC that it not only handles the boot process but it also contained information for the DVD-ROM, and the pinout showed that there were two Chip Enable pins on the IC, presumably one for each function. I connected a logic analyzer to both points on the problem board and collected some information during a boot cycle, and then performed the same sequence and capture on the good board. The results showed a burst of activity on both points for the good board which then quieted down, but on the bad board the activity continued to cycle and never finished. So it looked effectively like a boot loop that was never finishing, and it would then make sense that downstream components may not be getting initialized and hence no display.
I decided to use an oscilloscope to take a look at the signals on the data lines of the BOOTROM to see if maybe any of the lines were stuck. There were certainly differences in the signaling on the lines between the two boards which made me think that maybe the BOOTROM was damaged. While reviewing the schematics around the BOOTROM I noticed there were three resistors connected to the chip. There was a single 100 ohm resistor on the CE1 line, and then two resistors in series on CE2, a 100 ohm and a 1K ohm. Before doing a chip swap to test the bad BOOTROM theory I worked through checking the values for the three resistors. Wait... three resistors? But on the board there are only two.... crap.
R509 the 1K ohm resistor was completely missing from the board. Looking back at some pictures I had taken while working through the modchip process I could see that the missing resistor was there in the original teardown, and then was gone after the modchip was installed. My guess is that while cleaning some of the pads for the BOOTROM in preparation for soldering on the modchip wires I must have swept the resistor away accidentally.
I found a 1K resistor that I could solder into place, and once everything was in place I booted the system.
Hours and hours of tracing and troubleshooting because of one errant swipe with the soldering iron. I was happy to get the system working again so that I could work through the modchip installation again and finally get the console to the point that I could use North American media in it.
A great console revived that otherwise would have had limited utility in the North American market. I hope you've enjoyed this multi-part blog series which has taken you through some of my troubleshooting steps. Each piece that I work on is an opportunity to learn something and further improve my skills at tracking pesky issues like this down.