This is another “Double Dragon” arcade game pcb.
This one is also a clone (“bootleg”) of the original.

During the self test, RAM and ROM was ok, but it stopped with an error (“63701 Error”).

A common fault that gives this error is the SRAM TMM2015 (IC22) that is used by the 63701.
I removed it, and put in a socket with a TMM2018 i got from a Choplifter spare parts board.
It made no difference.

Another common fault for the “63701 Error” is the 74LS74 (IC39) next to the 63701.
I removed it, and put in a socket with a new 74LS74.
This solved the problem with the “63701 Error”.
The game now shows its startup screen with the Dragon, and the music plays.
Great, i thought. 🙂

But when the game play demo started, there were background and music, but no sprites..
It also did no side scrolling, so it seemed not to be running.
But after a minute or two, the sprites showed up in their initial positions.
Not moving at all.
After another minute or so, they moved one position, and froze again.
So it seemed to be running, but halts irregularly between the moves.
(Sometimes the screen went garbled after a while, but the music continued to play.)

Interesting.. 🙂

Noted that pin 2 (/NMI) on the 6809 CPU was at 3.3v all the time with no changes at all.
Compared with my working Double Dragon pcb, and on that board it was at 4.4v, with sporadic “LOW:s”.

I followed that pin to a 74LS74 (IC73, although on my bootleg version it is marked IC72 on the pcb.).
I piggybacked a new 74LS74, and tried the game again.
It now worked normally.

So i removed it, and put in a socket with a new 74LS74.

This board is now repaired. 🙂

This is a “Double Dragon” arcade game pcb.
It´s a clone (“bootleg”) of the original.

This one turned out to be an easy fix.

It did not boot, instead a garbled screen was all i got.
Strangely enough, when powered on for like the tenth time it booted right up and worked fine. (?)
I tried to start it up again and the garbled screen was back.

Apparently something to do with the initialization of the board.
When i took a good look at the board around the CPU that is used for the initialization, i noticed a capacitor that had one leg disconnected.
Turned out it was the decoupling capacitor for the +5v.
I changed the capacitor to a new 10 uf capacitor, and powered up the board.
It booted perfectly.
Tried it 3 more times, and it worked every time.
This board is now repaired. 🙂

I have another Double Dragon board that will be a more powerful enemy, because it complains about the large 64-pin chip (HD63701YOP).
More about that board later. 🙂