Another Capcom ZN-2 with black screen

[Space]

Hi all,

I have a ZN-2 board that has no audio nor video output but the ROM board works when connected to a working A-board.

I didn't find any traces of leaks from the caps from a visual inspection, they all seems in good conditions. Also could not find loose pins on the CPU and GPU chips either.

On the Jamma edge connector I measured 4.8 V on the bad board, on the working board the same PSU read 5.02. I did increase the voltage to read 5.2 on the bad board but changed nothing.

I've compared the voltage of a few caps from the working A-board against the bad one and they all have the same lower voltage. I'm not so confident about their measurements, I used the multimeter function of an oscilloscope (a Tektronix one) and on the working board they were all 5.6 V (I've left the note with their position in my office) and on the bad board I measured 4.8 V, again on all of them. Am I wrong expecting to read 3.3 V or less on them?

Anyway, as suggested by @Hammy in an old thread, I checked the Vcc on IC406 (pin 20) and instead of 3.3 V I measured 400 mV. Now, what should I check upstream of the IC406 or any other suggestion?

 

[Space]

Am I wrong expecting to read 3.3 V or less on them?

Replying to myself: "utterly wrong!". ^O^

Anyway, seems I've found at least one perished component on the board.

I've started with measuring voltage on the PQ30RV31 voltage regulator (IC504): P1 input reads 4.90 V and that's expected and OK, but P2 output and P4 vref read basically 0 V, not good.

That doesn't mean the IC is faulty, according to the data sheet the IC has protection against over current. Guess what, for the first cap downstream (C503) I don't even need to measure its ESR as it looks like it's shorted, on the multimeter it gives continuity. It passed visual inspection tho...

It's marked 100 uF 16V 85°C, looking on the web the M enclosed in a square points to Panasonic/Matsushita.

You guys have preference for a replacement or any 100 uF 16V 11x5 mm capacitor would do the job?

 

[kuze]

Following as I have a similar issue with my Capcom ZN2 mobo!

 

[Space]

I've ordered a few caps and while waiting I removed the C503 cap so I had the chance to test it out of circuit. Guess what? The cap is not defective, the ESR tester measure around 90 uF and testing for continuity the 2 pads' left empty by C503 shows a short.

I suspected It was too easy.

So this is a picture's detail of the zone around C503

This is the back, I've marked the pads 1 and 4 of the voltage regulator and A and B of C503, as I was trying to trace this zone:

Pin 1 is the input of IC504, the 5 V from the JAMMA edge, pin 2 is vout and should be around 3.3 V, pin 3 is ground and pin4 is vreg.

I removed IC504 to exclude it was the cause of the short, but no dice, pads A and B still shorting.

So in turn I proceeded to remove C350, L301, R504 (R502 was already unpopulated) and C504: A and B still shorting.

I've measured the resistance between A and B and it's 0.1 Ohm. With a short on 0.1 Ohm it looks like a failed ceramic capacitor, any objections?

Next step I want to try is looking if in the colleagues have a thermal camera, it was suggested to inject a 1~3 A current at <= 1 V with a bench PSU to spot a component warming up.

I'm open to other suggestions... ^__^;

 

[Hammy]

Yeah that sounds like a shorted 3V rail, so you can either remove components until the short goes, or try the heat method.

 

[Space]

Weekly update.

I found the short, two CPU's pins where bridged with a smudge of solder, it probably happened when I reflowed both CPU and GPU. Now the voltage regulator IC504 pin 2 is 3.4 V and I can measure the same tension on IC406 pin 20.

So I'm back to square one: when the PCB is powered up with the supergun I can see the TV that get the sync signal (the green "TV" symbol on the screen disappears) but I still get no audio nor video.

I think I've found online some repair manuals for the PSX, my next plan is to ignore the PSX PSU and CD-ROM checks and see what's suggested for RAM, CPU and GPU.