Duo RX produces horrible noise instead of ADPCM samples

[xnopasaranx]

Hi there fellow enthusiasts. I have a PC engine duo RX I recently imported from Japan and it just won't behave... Hucards work without a hitch, but when testing cd games I noticed that certain samples will only produce noise and screeching sounds, or start playing and then turn into hellish screaming noise. For example when I load up Dracula X there is this creaking door sound, but it always starts sounding fine and ending in ear bleeding noise, while the shattering glass samples in the first stage only produce pops and crackles. First I thought it was a red audio problem, until I calibrated the laser using and oscilloscope and indeed the audio tracks sound crisp. Audio CDs also play fine even on the outer tracks.

For good measure I decided to replace the caps and found a lot of corrosion near the ADPCM IC and one of the pads (I believe it's C879) has come off the pcb eventhough I took great care when desoldering (I use a vacuum desoldering station). Bridging the connection was no problem and I was happy I got the board done tonight, but the sound issue remains and I do not know how to proceed any further.

Does anyone here have an idea what I should be looking for? I was not able to find anything by googling and also tried searching the pcenginefans forums that remotely matched my issues, it seems everything revolves around cd audio issues...

[keithcourage]

Unfortunately this is usually the sign of a faulty chip on the board. Usually the IC501: NEC D91317GD

However, there is still a chance this could be caused by bad traces to the chip as well. Start looking for Black or corroded looking traces for said chip.

Sometimes this problem can be caused by a bad PCM chip 5205 but I've only encountered that 2 times over my 13 years of working on these things. More likely to be bad traces or a faulty IC501: NEC D91317GD

[xnopasaranx]

thanks for the answer! I will try to reflow the pins of IC501 first and see if a solder joint has gone bad, anything I could see with the oscilloscope? Not sure what to look for exactly and on which pin. I will also see if I can find a replacement for the chip.

EDIT: replacement from a donor would be an option if it really is IC501... but since I found so many small damages due to the leaked caps, I will look for broken traces next like you suggested. Reflowing IC501 has not helped and I wasn't able to find a blackened trace but might have overlooked the culprit.

I wish I had a proper pinout of IC501: NEC D91317GD but the only reference I can find is a dead link here in a link collection thread

[xnopasaranx]

wow... I wanted to continue debugging this and today tried to adjust the pots one more time, because the unit decided not to spin up cds anymore for some reason. I got an eye pattern going and tweaked a bit, then all of a sudden the console doesn't want to work at all anymore but only shows garbage on screen when switching it on. This is the second duo I imported and sunk money into, I am truly getting sick of these pieces of shit. What the hell? I didn't touch anything, hucards were working perfectly up until now. Why oh why did I invest so many hours and euros into another doorstop?

Also, I was not able to find any bad traces, even had a look with a thermal imager but nothing looked out of whack...

So could this mean that the D91317GD has finally died? If this is the case, there is no reason not to try transplanting an IC501 from another dead Duo onto this one I guess, it's broken anyway.

FFS I have spent several hundred euros on games alone the last two months, in anticipation of playing them on my new Duo RX... I guess I'll just wait for the analogue duo and have a working fpga clone that I can trust will work for a long time.

EDIT: Okay this seems to be either a crack in some via somewhere that I am unable to locate or a pin that has a shitty connection somewhere... After dropping the console from a few centimeters to shake it up a little, I was briefly getting a boot screen again, but it showed random garbage instead of "push run button" on each blink. what could this be? now it's back to reliably showing garbage only...

[keithcourage]

Does this happen with h u games as well or is this only affected the CD bios screen?

[xnopasaranx]

hey there, thanks for answering again. apparently it affects hucards as well... they start with totally garbled screen and playing music at like twice the normal speed.

[keithcourage]

Okay, if the garbled screen is effecting everything then check for bad traces or poor solder joints for the Work ram(IC904: SRAM: HSRM20256LM12
IC905: SRAM: HSRM20256LM12) or the HU6270.