Turbo-Duo R's with BIOS screen not loading...is this common?

[Yoder]

Yeah, good point ;-)  Ok, for posterity, the automatic volume control (AVC) on the PCE Duo-R is IC505 and is a Mitsubishi M51131L.  It's a zip chip (with all 16 leads on the side of the chip) and is located right underneath the CD assy.  http://www.datasheetarchive.com/M51131L-datasheet.html.  I'll see if it's getting voltage and maybe if I can get some sort of audio out of it...that's when it's nice to have a scope :-/ 

[thesteve]

or a sound probe

[Yoder]

That's true.  I was thinking of using some cheap amplified speakers to poke around but I have some opamps that I can probably use to build a little amp which may be better.  I came across this circuit that I could probably use:  http://www.talkingelectronics.com/FreeProjects/MiniBenchAmp/MiniBenchAmp.html.  I'd think a little transistor amp would do it too.

So I checked the leads on the SMT DAC chip and they actually all seem to be good solder joints.  I then checked the voltages on the AVC.  Looks like I have 7.7V in which I guess is enough...spec is 8-12V. The other leads show about 3-5V, which I guess is ok based on the supply voltage.  I'll need to listen for some audio in and out of this thing next.

[thesteve]

your voltages sound right.
that amp circuit wont work with most opamps, so you would need the right chip

[Yoder]

cool.  I was glad to see that the chip was not dead.  oh yeah, I have an LM386 around...I was just thinking that a different (simpler) one could be made with a transistor.  That gives me two tools I can build with my geeky Radio Shack electronics kit ;-)

[BlueBMW]

This is a quick and dirty audio probe steve showed me how to make.  I just used an rca jack and connected an rca cable to a tv to listen to sound.  Works perfectly!

[Yoder]

Cool, thanks (and to Steve too)!  I have plenty of hacked RCA cables around :-) 

[Yoder]

The audio probe works well :-)  I got audio right off pin 17 of the 6280 as a test.  Unfortunately, I have no audio coming out of the LC7881 DAC (and of course none going into the AVC).  I confirmed that the DAC has voltage and ground.  There are four digital input pins on one side, and I can't seem to trace two of them anywhere...and the traces don't look pretty from when this chip changed out at some point.  The other two go to a large NEC IC (D6378GF), but I'm not sure where these two in question (DATA and BCLK) should go. 

I don't suppose there is a schematic for the CD audio section is there?  I know that Charlie is putting something together, but I don't think it deals with this part of the circuit.  If I was positive these two traces did lead to the pins in question, I'd just connect them to the chip from a point further upstream, but I don't feel comfortable doing that until I get more information... Time to get the logic probe and see if there is at least a digital stream coming from the two pads I saw further upstream on these traces.

That's for another night...

If you guys have any thoughts, I'd love to hear them.

[Yoder]

Ok, I just cleaned excess flux, and it does look like two traces leading to the DAC are black in color and feel rough when I drag my sharp probe over them...like they're oxidized underneath  And I don't have continuity across this 3-4mm or so length to the next pad in each trace.

So this sounds like a place to start :-)  If I can get a pic tomorrow night, I'll post one...but those traces are pretty tiny.

[thesteve]

tiny traces deserve small strands of wire to repair
take a multi strand wire and use single strands to jump the bad traces.
expect the same issue around system rom

[Yoder]

Thanks, I really appreciate your input...I'm glad I found the "black traces" that you mentioned earlier.  Yes, I'm gonna use wire from either network cable, phone, cable or an old parallel cable (they can be really thin).  Hopefully my new soldering station comes in ASAP...I ordered some small tips with it.

I haven't located the ROM chip  yet...anyone have any pointers?

I'm uploading a pic of two angles of the bad traces.  What I'm not sure about is whether there is something on the bottom of the PCB that's not getting signal also...you can see that the corrosion extends past those through holes.  One step at at time, though...

[thesteve]

push a wire through the through holes and solder both sides to be sure.
corroded through holes are often intermittent.
as for the rom chip, im not sure what chip they are using.
also the rom uses a memory bank (also present in the system card)