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Time to give up? (Video Issues Now)


Mtlatc
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OK. So, I managed to fix my internal power board.  Plugged it into an LCD TV via two RCA jacks and the result is posted.

 

I only had a few minutes to bask in my childhood before I had to turn it off for the night. (I know it looks horrible but that's not an issue I'm worried about right now.)

 

I still have to disassemble the whole system again, and besides thermal paste, I need to take the keyboard off and give it a good cleaning. Here is a photo of the bottom of my keyboard. 

 

My question is, why might I be getting the letter "H" when I type "N" && "J" when I type "M"? That was one thing I noticed right away.

 

Thanks for any input you may provide.

IMG_4327.jpg

IMG_4232.jpg

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You are somewhat in luck--that is NOT a Mitsumi keyboard. There are still two potential styles of keyswitch though: Alps, which are sealed; and several manufacturers with a set of metal fingers below the keytop. The metal finger type seem to have the greatest longevity, although they do need an occasional (careful) cleaning. On your weird key issues, if they continue after you've cleaned the keys, you might want to check for weird wire issues in that short cable connection. They sometimes get brittle and wires break. . .

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21 hours ago, Mtlatc said:

My question is, why might I be getting the letter "H" when I type "N" && "J" when I type "M"? That was one thing I noticed right away.

The keyboard I/O schematic should help sort that out.

 

"N" and "M" share a row and each share a column with their respective replacements; their respective replacements, "H" and "J", share the same row.  There could be some interaction between pins 4 and 5 of the keyboard cable, or UP FIRE and LEFT of the joystick, also respectively.  Without a more thorough inspection, I would expect similar behavior from other keys in the same row as "N" and "M".

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@Mtlatc Oh well, blows that theory.

K and L don't print < and > ?

Have you pulled the Key caps and looked at the key switches?

When you get the metal casing off, look for possible contact signs around the keyboard connector and the Joystick port.

My bet though is that it's something on the keyboard. If INT3 and INT4 were shorted, I believe you'd get other strange key presses. I suppose it could be the 9901 chip or maybe some of the resistors, caps or coils or even 74LS156. @OLD CS1 mentioned the Joystick connector, you got one plugged in?

image.thumb.png.311d29bbed2a3eeb1096924efa21fdcf.png

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1 hour ago, Duewester said:

image.thumb.png.311d29bbed2a3eeb1096924efa21fdcf.png

There is (at least) a discrepancy between this schematic and the one @matthew180 provided which I used.  In the one Matt posted, the implicated keyboard rows go to pins 4 and 5 on the keyboard connector, which then go to FIRE and LEFT (I was incorrect in my original read, which I have fixed in the post.)  However, this schematic shows pins 4 and 5 on the keyboard connector go to pins 5 and 4 on the joystick connector, which are labeled LEFT and RIGHT.  This is just a "noticing" post.  I will pull the paper schematics out later to reconcile.

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I’m going to take a look at it in a few minutes but I figured I would post this photo. Top line w/o Alpha Lock second line with Alpha Lock. Started with 1 and went left to right. As you can see when I get to the bottom right I start getting the issues. 

F8473573-90CF-486F-8876-6230B3327F3A.jpeg

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1 minute ago, Duewester said:

Is that an intentional Space between 0 and q or is the space a result of pressing the += key? If it's a space result from +=, I'd say look for a short across INT3 and INT4. 

Thanks I will take look because as you have surmised that was pressing the += no intentional space. 

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@OLD CS1 @Duewester It is because of folks like y’all that this forum is a great resource for the community!
 
Once I got the machine apart, and cleaned really well, I was still having all of the same issues. 
 

It was the joystick discussion that allowed me to find and fix the issue. Now mind you I don’t even own a joystick yet. Lol. I was waiting for that purchase until I made sure I could get the machine working.

 

I decided to inspect/clean the joystick port as a “why not” As you can see below pin 5 was bent and shorting pin 4. Taking care of that took care of all the issues I was having on the entire keyboard.

 

Thanks for responding and discussing the issue because without that discussion I doubt I would have found the issue. 
 

B06F5FD0-69A0-42B1-96E9-03FCE67701AE.thumb.jpeg.707cd1ad5e1d5595a96f83d131822eef.jpeg

DBAA1852-C6BC-46EC-90C2-DC09D8AE4391.jpeg

2766E52C-9FAE-40CD-837E-531E07249D3F.jpeg

Edited by Mtlatc
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Thought I had it up and running. Now this.

 

I was coding an BASIC program and my video began to flicker and do really weird things.

 

I have attached an 5 Second video clip for anyone that may have any ideas.

 

I’m really starting to feel like this isn’t going to work out and I am very frustrated .


All help is welcome. 

Edited by Mtlatc
More info
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  • The title was changed to Time to give up? (Video Issues Now)
17 minutes ago, jedimatt42 said:

Maybe a few words instead of an all pronoun topic and post? Some info about why anyone should watch the video attached... 

Absolutely correct, even when we’re frustrated we should give folks enough information to act on. Thank you for the real reality check. 

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6 minutes ago, Duewester said:

Heat sink on the VDP. Should have some form of cooling it or dissipating the heat. The 9918 gets pretty toasty after awhile.

I see you have the main board out of the case.

Does it clear up if you let the machine cool down after power off?

It had Thermal Paste on it. I cleaned the chip and socket just to make sure. Unfortunately, after cooling I still have the issue. I’m wondering if it may be the crystal… of course it may be the 9918.

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VRAM is definitely solid, that's the usual candidate. ;) If the heat sink is making good contact with the VDP then it really looks like a broken wire in the video cable... do you have another one to try?

 

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This may be the problem. SAMs list it as an oscillator 2-4.5uH but I can’t seem to locate anything like that on Google. Does anyone know the replacement for this?

470441B2-DB4B-42CC-9D1A-B59553B7E79C.jpeg

Edited by Mtlatc
Correct uH
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