May have just blown my FX1DJ & A1F - looking to repair. Suggestions?

Supporter (10)

18-10-2019, 17:15

Hey everyone, I'm a new user here so I apologize if I'm posting this in the wrong section. I'm having a few issues with two MSX computers and I'm hoping someone here can help.

A Japanese friend of mine recently sent me a few of his old computers, and after reading it was okay to power a Japanese MSX using American mains, it would seem as though both my newly acquired Panasonic A1F and Sony F1XDJ refuse to display a picture. I've since purchased a step-down converter hoping this would solve the issue, but they are still refusing to boot. A third computer I was given seems to work fine on the step-down, and it was the only one I didn't try to power on without the step-down. Odd coincidence? Probably not.

So here's what I know:

- The power lights work on both the A1F and F1XDJ, and the Ren-Sha Turbo light indicator works when moving the slider.
- The screen is a solid black on both computers. The TV recognizes the signal, but nothing happens.
- The F1XDJ made a lot of pretty bad rumbling noises when powering from US mains and the step-down.
- The F1XDJ smelled like burning electronics for the two or three seconds I initially had it powered.
- The drive doesn't initialize on either the A1F or F1XDJ when a floppy is inserted when powered on

I opened the F1XDJ to see if there was any obvious burning, but all *seemed* clear. I'm stumped. Both computers were confirmed working before the shipment.

As there anything I can do, or did I just fry two computers? Stay save and use a step-down, kids!

Por Meits

Scribe (5650)

18-10-2019, 17:41

In case of the Sony, did you check underneath the diskdrive? Is there corrosion on the HIC board?

Por Alexey

Guardian (2446)

18-10-2019, 20:54

I've read somewhere that the US mains voltage can go up to 125v, so for the 100v-rated Japanese old electronics 25% more voltage is definitely stressful. However, if the power indicators still work, then the boards are getting at least 5v from the power supply. So at least the main voltage regulator is intact.

You need to measure the voltages on the board first. If all 3 voltages are present (+5v, +12v and -12v), then the next candidate for checking would be the small video converter board (as Meits suggested). The leaked electrolytic capacitors could have badly damaged the board, so that it must be repaired.

If the HIC board is still OK, my next bet would be on either bad ROM or RAM chips. If you have a memory mapper cartridge, you might want to try to boot the computers with it. If a computer boots with an external memory mapper, then the on-board RAM is busted.

Another way to test a computer is to insert any compatible game cartridge. If a game starts, but a computer doesn't boot to Basic without it, then the RAM could be busted.

Por MSX_User

Supporter (10)

18-10-2019, 20:44

I don't have a mapper cart, so I just popped in a game cart. It works fine on the third Sony MSX computer, but it doesn't work on the A1F or F1XDJ - still a black screen. I checked under the drive last night and I didn't see anything out of the ordinary (discoloration/fuzziness/green death) but I'll check again. That loud buzzing/rumbling was coming from under the disk drive.

Everything worked right before it shipped over, so I'm thinking I fried something important, unless of course the caps somehow became a problem on it's way over? I should have used a step-down regardless of what the Internet says.

I'll test for other voltages tonight.

Por Pencioner

Paladin (993)

18-10-2019, 21:32

Which cable do you use for video output? Did you try composite? If your SCART cable is Japanese then your pinout is not correct (despite the same physical connector Japanese uses standard called JP21 and it is not SCART). What is the third computer? If third one is used with the same cable and it is working, then it is definitely not a cable problem, but if third one is MSX1 with only composite output then you might have to check that first - try composite on FX1DJ & A1F and if it works buy a proper cable

Por MSX_User

Supporter (10)

18-10-2019, 22:17

I'm using a standard composite out into a PVM and the third computer is a Sony F1XD. It's definitely not a cable issue.

Por sd_snatcher

Prophet (3092)

19-10-2019, 19:49

Does the CAPS LOCK and Kana LEDs work on any of the computers?

Por MSX_User

Supporter (10)

20-10-2019, 05:34

It looks like the Caps Lock and Kana LEDs do not come on when the respective keys are pressed on both the A1F and F1XDJ. I still have yet to test for proper voltages, but I assume this is a pretty good indicator of the computer missing more than one power rail?

Por rderooy

Hero (583)

20-10-2019, 12:25

MSX_User wrote:

Not an electronics expert, but since your power LED works, but the keyboard LEDs do not, I don't think it is an issue with not getting power, but rather that the system does not initialise far enough for the keyboard LEDs to work. in effect, I think it is basically "hung" booting up.

Por MSX_User

Supporter (10)

20-10-2019, 15:58

Would plugging a Japanese unit into a North American mains cause this behavior on two different computers, though? I won't know for sure until I measure, but with the little experience I do have with electronics, I'd say it's possible to blow more than one power rail while leaving another intact. My initial thought was that the keyboard is pulling it's power from one of the faulty sources.

Por sd_snatcher

Prophet (3092)

20-10-2019, 16:29

Quote:

Would plugging a Japanese unit into a North American mains cause this behavior on two different computers, though?

No. People have been using Japanese MSX computers in Brazil (127V) for more than 30 years without any problem. Only the models from Toshiba are known to be picky about the voltage. The two models you're using are well known to take up to 127V without blinking an eye.

In the case of Toshiba machines, then yes you MUST use a step-down converter. Their power supply is poorly designed and gets hot even when used at perfectly normalised voltages. Check this part of the thread for some recommendations on how to improve their power supply.