While I was laying out a PCB that has 3 of them on it for RGB, I decided to check out the newer IC in the position of the old IC that the Toshiba already has for the regular composite video input isolation. The old IC is the TLP551. This didn't work out well for me; it caused something to blow up. There was a little spark in the neck of the CRT and then I got nothing on the screen. I pulled all the boards and put the old IC back and checked voltage levels around the system and everything seemed to be back in order again. However, after some time passed, the raster started to fade out in a weird way.
Luckily, I have two identical TVs, so I swapped the know working chassis into the broken one, and I confirmed that the issue is on the PCB and not the tube. I think I probably damaged the main video IC, or possibly the jungle IC. It's not a huge issue as I have extras for both. This set is a long-running project set of mine, and I have extras for many, many parts to swap around, etc.
So what I still don't understand though, is why the new IC caused a problem in the first place. I don't see how it's different in any way that would cause a problem.
The forward voltage and current transfer ratios are more or less the same, the pinout and internal construction of the ICs are the same. For all intents and purposes, they appeared to be the same IC made by different companies to me.
So I'm wondering if I just made some kind of huge boner mistake like there was coincidentally a huge solder blob shorting something out that fell off the bottom of the PCB when I swapped it back? I used a socket when I installed the new IC, and I kept the socket there when I swapped back, so the current (working) conditions are the same.
I used the old AV input PCB (its a daughter board) with the swapped in PCB, so the whole section of the PCB that I used to swap the ICs is the same now as it was before. Only the main chassis PCB is swapped in and different. That's how I know the problem is on the main PCB and either the Video IC or the Jungle IC (or possibly another random part, but the failure mode looks like an IC failure to me).
Can anyone tell me why the 6N136 would be different in a catastrophic way from the TLP551?
This is the area of the circuit below, and here's a link to the two datasheets. The other IC in the folder is the audio IC, which I also swapped. The OG is a TLP521, and the replacement is a TLP785. As far as I can determine, these two parts are exactly the same. They have identical ratings and they are both Toshiba parts. But those datasheets are both in there FWIW.
