GSCARTSW Rescue - 12/15/2022

This is sort of a side project, but also a very important once since a lot of my plans hinge on having a good RGB switch. The RGB modded trinitron I own works perfectly, but suffers from only having one input. In order to tie all of these consoles to the TV and making it user friendly enough that children can play it I knew I would need a good automatic SCART switch. Enter the GSCARTSW. Revered as one of the best switches on the market, in 2022 with part shortages, it has become unobtanium. As chance would have it, I managed to find one that was broken on ebay. In hindsight, I probably should have passed and waited as it ended up taking considerably more time to fix than I anticipated. Makes for a decent story though. 

I bought the cheap broken GSCARTSW lite 1.5 off of ebay hoping for a simplish multiplexor replacement. The seller ended up being a prominent member on r/consolerepair/ and I was disappointed to find they picked apart a large portion of the power stage(s), failed to fix the issue, and hastily put it back together [incorrectly] for the sale. I suspect they never got to the multiplexors due to not being familiar with the supergun spec violations that kill them, or wouldn’t wait for parts availability.

I’m happy to say, the root cause of the issue was a short in blue / green multiplexors U1/U2. I also ended up replacing all of the SP6661 charge pump vregs because I found that the previous tinkerer incorrectly reworked one 180 degrees out of alignment and I didn’t trust any of them after that.

The initial symptoms of the switch when it arrived post purchase was no LED, ~1v on the 5v rail, and a blistering hot U17 charge pump vreg.

U17 was found to be 180 degrees out of alignment so that was replaced along with U18 and U19.

With the vregs fixed, I started removing the chokes to determine what was shorting the 5V rail to ground. I determined that the multiplexors U1-U4 behind L3 & L7 were responsible. After waiting ~2 months for mouser to restock, I received my replacement 78-DG4051EEQ-T1-GE3 multiplexors and started reworking. ~100ohm short was still present after removing blue multiplexor U1, but gone after removing green multiplexor U2. U1 may have also been shorted, but U2 definitely was because after removing these two components, I got the 5V rail back with L3 & L7 installed + the return of the LED (indicates that the FPGA lives)

Replacing U1 and U2 netted a fully working unit with one caveat…

I noted the current TVS diode D1 was getting hot enough to melt plastic which in this case was the top of my NES frontloader the GSCARTSW was sitting on while testing! D1 was one of the components the previous ‘fixer’ replaced and they also included a few spares with the sale. Unfortunately I don’t have the OG TVS, hence my concern.
I suspected the diode was incorrect and undersized based on evidence I gathered, but without a good support system for this switch I didn't know where to get answers.
I ended up posting a shmups and to my amazement got a reply from the switch creater superg who confirmed my suspicions and provided replacement part numbers for not only D1 but also the chokes that were looking worse for ware. He also suggested replacing all of the multiplexors to be on the safe side of things

After a final order and replacing all the components above, I'm proud to say the switch is 100% fixed and working perfectly.