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Very dark and poor RF output? Look to the 74LS32 IC...


CrossBow

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A few 7800s have been sent to the ITC for repairs and eventual upgrades. Before any upgrades are done, I always get the consoles back to fully working stock condition first. This 7800 was working but had very dark, fuzzy, and as such very poor RF output. Now yes, RF output doesn't look that hot on modern displays to begin with, but this was obvious something was wrong. After looking over the board for a bit, it became apparently that someone in the past had replaced or tried to replace the 74LS32 IC chip that resides just above the Maria IC on the 7800. This chip handles quite a bit of the output signals from the Maria and through to the RF section so this chip not working or being faulty will produce no picture output conditions, scrambled looking picture output or similar video output related issues.

Upon removing the chip, I quickly found 3 main problems as the cause and they were all due to poor connections due to damage from when the chip had been replaced prior.

Here is a picture of the top of the board with the spots identified that were the issues.

78-2_74ls32_top_brd_damage.jpg.9eea58e94ec4f6e8f3b96c5f7ccff9b2.jpg

 

I will state that the bottom of the PCB actually looked much much worse with lots of burnt PCB marks indicating that perhaps much too high a heat was used when trying to remove this chip originally. But, only a single VIA pad was  damaged on the bottom and wasn't connected to anything so it wasn't critical damage.

I used three very small sections of 30awg solid wire kynar to repair these broken trace sections. I then placed a new socket on top of it all and then soldered it all back down into place. The original 74LS32 tested good on my chip tester so it was put back into service in the new socket and now everything is good to go! BTW, while a UAV install would bypass a bit of these signal lines, the sync and Lum1 are processed through this chip and so if that chip is faulty, it can result in affecting or preventing output from AV upgrades as well.

78-2_74ls32_repair.jpg.54411d459574451b8cfa447ae19217c7.jpg

78-2_74ls32_repair2.jpg.0dd1927de5bb6d705441f788e0f30be3.jpg

So yeah... if you find yourself with some squirrely looking RF output but can still kinda make out a picture, you might look at this IC as being a possible part of the problem. Again, in this case it was due to what I assume was the chip being replaced out in the past, but whomever did the previous work damaged some of the traces and via pads in the process making the replacement not making contact where needed.

 

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