Aug 252015
 

Got this Sunset Riders PCB always in a trade with my friend Ifog:

Sunset Riders_PCBJPG

Board was really in mint condition but, as my friend warned me, it was faulty.

Actually when I first powered it up it played perfectly but after some minutes it showed an issue where some parts of graphics had wrong colors (pinkish, I’d say) :

color_issue

Since I have repaired other similar Konami boards with same issue, I already knew where start to look at.Palette RAMs are two 2018 devices @13D and 14D:

pallette_RAMs

I probed them with my oscilloscope but didn’t notice anything abnormal (though they were hot at touch), also piggybacking them didn’t change anything.So, I went more ahead in the palette circuitry following the path of the data bits of these RAMs.Just before the generation of the three RGB colors there are some open-collector buffers (74LS07):

palette_circuitry

Probing the one @8C with my scope, I found discrepancies between input pin 3 and output pin 4:

7407@8C_waveform

Once desoldered, the IC failed on pin 4 indeed:

7407@8C

Comparing on a tracer the bad output with a good one, you can see how the internal junction was altered (good one on the left of the below picture):

7407@8C_comparing_tracer

Fitted a good IC fixed the colors.

Success!

 Posted by at 11:31 pm

  2 Responses to “Sunset Riders repair log #1”

  1. Good job caius, you are once again ‘da man’!!

  2. Thank you, I’m only a man who works hard!