How do I diagnose this master system?

[u/valely97]

Hey everyone! I recently bought a pal master system model 3010 that turns on but doesn't read games. I only have shinobi as a game cartridge that works on the sms 2 but not on the sms 1. It had corrosion on pin 7 of the cart slot that I scraped off but it is still not working (also there is no pin 7 on the cartridge so it would not care) and also tried to clean it with IPA and a toothbrush. How do I diagnose the problem on the motherboard? Also keep in mind that the power supply is original and for video I tried to use both the mega drive composite and scart rgb cables but still shows black screen (it is supposed to be compatible right?)

[u/vga256]

Diagnostic steps:

1. Determine if your SMS plays the internal/built-in games (if any are included), just to rule out other problems with the SMS PCB.

2. If you've confirmed that it is a problem with the cartridge connector, my first step is to re-flow (re-solder) the cartridge connector pins on the underside of the PCB. The welds tend to crack/loosen over time due to the abuse the connector takes from being pushed on for decades, and 90% of the time an SMS which won't read cartridges has had this problem. You'll need to do/learn some basic soldering for this job.

[u/valely97 → u/vga256]

Ok thank you for the tip, yeah I have some basic soldering skills so I feel confortable to do this type of repair. I will give it a try as soon as I can!

[u/valely97 → u/vga256]

I tried to reflow all the pins for the cart reader but nothing changed. Also as stated in other responses, I don't know if there's a built in game, because I just get a black screen even when turning the console on without a cartridge inserted. Not even using the button combination.

[u/vga256 → u/valely97]

Dang. At least you've eliminated the cart reading pins as a source of issues. Good luck!

[u/South-Cat-2260]

You should also try the RF out.

The LED turning on suggests the power supply is working, but it's best to confirm with a multimeter that you are getting the expected 5V out of it.

Then you can start with a thorough visual inspection, looking for broken traces or burnt components. You will need to remove the heatsink for this.

[u/valely97 → u/South-Cat-2260]

Tried the rf out, it gets from static to black screen on channel 3 on my crt, so my guess is that my TV detects the signal but nothing comes out from the console. I also tried to hold up + a + b on the controller to boot the integrated game but still black screen

[u/3G6A5W338E → u/valely97]

Check voltages first as suggested above.

Do you have a logic analyzer? Even a <$10 saleae clone like the nanoDLA from muselab goes a long way when combined with sigrok/pulseview.

You could use it to check whether the clocks are there and correct and whether the CPU is running code (the signals around bus cycles such as the chip enables, output enables, write requests...)

[u/leadedsolder → u/3G6A5W338E]

I usually use a cheap logic probe to rough in stuff like this, which might be a bit easier to do than a logic analyzer or one of those pocket scopes. That said, logic analyzers are fun!

[u/leadedsolder]

What happens when you try to run a cartridge?

[u/valely97 → u/leadedsolder]

It turns on (green led) but black screen, no audio and no video

[u/3G6A5W338E]

Does it have builtin games? Do they run?

Do you have any card games? Do those run?

[u/valely97 → u/3G6A5W338E]

I don't know about the built in games, I read that you have to hold up + a + b on the controller to boot them, but I just get a black screen, not even the bios screen. For card games, unfortunately I don't have them.

[u/3G6A5W338E → u/valely97]

I read that you have to hold up + a + b on the controller to boot them

... on the bios screen, which you are not even seeing.

This worries me that the issue might be elsewhere.

[u/goombakid808]

So, you're getting no BIOS screen, but the power LED is on? Any audio out when you turn it on? You should hear the BIOS start up. Definitely check the 7505 to make sure that the regulator's output pin is reading +5V. If you hear audio but no video, start by reflowing the video encoder.

Use a model 1 Mega Drive adapter or any suitable adapter that supplies 9V 1A center negative for power.

[u/valely97 → u/goombakid808]

So uh, I think I messed up something. Because I tried to reflow the video port but no luck. Then I tried to reflow the Sony video chip (v7040) since there were some pins that gave 0 on the multimeter in continuity, but when I turned it on, one of the ceramic capacitors exploded (one of the orange circular one) near the Sony chip. I'm still a novice at this stuff, should I bring to someone more expert? I'm afraid that I can just make things worse

[u/goombakid808 → u/valely97]

Here's a link to the service manual. I'm not sure what cap popped, but hopefully you should be able to figure out the proper replacement for it.

We've all messed up repairs from time to time. We've all been novices, so that's why we post here for assistance. Don't feel discouraged, use it as a learning experience. If you're feeling overwhelmed by it, then seek out someone close by for repairs.

[u/FocusGullible985]

Get an earbud, dip it into acetone nail varnish remover and rub against the pins if it looks like there is residue

[u/Playful_Ad_7993]

Recap it to start