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

[Yoder]

This is my first post, but I've read lots of threads here :-)  This place is a great resource with lots of really experienced members!

I currently have a TG-16 that I brought back from the dead by bypassing the RF output and building an a/v cable based on Jibbajabba's website.  (Thanks Jibbajabba).  I also have a PC-engine that I ordered from Japan...it's super cool and I even Retrobrighted it so it looks like new :-)  I plan to do an S-video mod to each of these when I get some time...been wanting to do that for a while now.

I have a few HuCards for each and a Tototek flash card, but I really want to play some CD games.  I'm considering purchasing a Duo-R unit that functions on the HuCard side and has a tested good laser, but has no CD audio (which I hope a re-cap my solve) and an issue where the onboard System Card BIOS doesn't load (requiring a System Card HuCard to load CD games). This one stumps me a bit.

I have read the archives and I don't see this come up much, and the one thread that I saw on it, never had a resolution.  Have any of you guys seen this before?

If I get it, I'll check the traces, look for leaking caps, etc, but I wanted to see what you guys thought.

Thanks!

[NecroPhile]

Welcome aboard!

I'd steer clear of that one.  It sounds like a Duo-R that fellow member Keith is selling; Keith knows his repair stuff well, so it's most definitely not going to be an easy fix.

[Yoder]

Thanks!  Such a cool family of consoles...always something to learn with these things with the different variants, Japanese versions, etc!

It certainly could be, and the guy selling them has been very honest and up front that he was intending for it to be for parts, vs to fix.  But, OTOH, he hasn't attempted a repair other than checking that the laser is good...if he had, I'd figure there would be no hope for me.  But you're right.  It might be risky.   He also has a Duo with no audio (at all) and at least a bad door switch ("Please close door" display)...maybe that one would be more straight forward. 

I do want to save some money, have a project, and have an opportunity to learn, but I would like to actually get something working too :-)

[GohanX]

The only time I've encountered a similar issue is when a duo-r has a really dirty cart slot and an Arcade Card plugged in, so it's like the system doesn't post a CD bios screen since it knows a hucard is there, but won't do anything since it can't read it.

Personally, I'd steer clear unless it was really, really cheap and if it doesn't work out you could keep/resell it as a parts system. There are always people who need good Duo R shells!

[Yoder]

Well, the work-around is to just put in a system card...not a huge deal.  Then I just have to deal with the lack of CD audio.  That could be an unrelated problem...hopefully a cap, a trace, an op-amp, etc.  Of course there could be a bad DA converter in there too, I guess.

The good thing is that it functions 100% on the HuCard side, so at worst, it would be an over-priced PCE.

It's not super cheap, but not super expensive, either, considering these go for $150 and up when they (supposedly) work.  Well against your advice, I'm gonna grab it   

Hopefully I'm not making a mistake.  I'll do what I can with it.  If I can fix the audio, I'll be happy.  I don't  mind having a system card in there to use the CD side of it.

[thesteve]

id suspect you have a related prob.
fix one fixes the other.
never seen one that couldnt load the bios, but worked right with a system card.
bios failure has been a problem with the system bus, and other CD related things didnt work either

[Yoder]

And I guess that could be a good or bad thing, depending on what's broken and how serviceable it is.  The console should be on its way now, and I just placed an order for a new soldering station with a few tips (got the CSI Hakko clone http://www.web-tronics.com/soldering-stations-csi-station1a.html), some decent desoldering braid, and a few other small tools, so I should be ready to work with it soon...or at least when I finish my last C project of the semester.

Should I go ahead and buy a logic probe?  I don't have a scope, so that may be the next best thing for looking at the digital parts of the circuit.  I can at least put one together on a breadboard...I think I have all the stuff for a simple DIY one for now...

[thesteve]

a logic probe will be a minimum for what your getting
scope is better but probe is quicker

[Yoder]

First of all, I appreciate everyone's responses    Steve, are you familiar with the velemann portable $150 scope? http://www.vellemanusa.com/products/view/?country=us&lang=enu&id=351263 If so, does it suck?  ;-)  Or would you recommend picking up an older Tek analog scope.  I see a few locally like a 464, 466, and a 561 for $100 to $150 sort of locally.  Would that be the way to go?  Space is an issue for me too, so the portable one would be great if it works.

I think the last time I used a scope was in 1995 in Physics II Lab...I'm gonna need to spend a few hours just figuring out how to use one before I even start :-/

[thesteve]

im not familure with that portable, but its specs say it wont work for you.
the pce runs at 11Mhz so your scope needs to be usable at or above 22Mhz

[Yoder]

Good catch, I didn't even notice it was that slow! You ruled that one out for me :-)

[Yoder]

Ok, so I got the unit today.  Exactly as described.  HuCards play perfectly.  CD games play but no CD audio.  No loading of BIOS/ROM, either.  I get a purple and or yellow screen (unless I insert a system card), exactly like I see flashing up quickly when  HuCard is inserted, but then the HuCard game loads after those two screens cycle.  So either the ROM is corrupt, the ROM data isn't making it through to RAM or wherever it goes next, or the signal that tells it to load it isn't right.  Almost looks like a region lockout effect that you see on NESs when the games don't load right due to a dirty 72-pin...you know, when you get a colored screen.

The CD audio definitely doesn't work, but I can see that the Sanyo LC7881M DAC has been replaced and it almost looks like there may a bad solder joint on one of the tiny legs.  I pushed down on it while playing an audio CD and I got crackles and popping but no real CD audio.  First thing I'm going to do is make sure that those legs all have continuity and then maybe reflow the solder on it.  I doubt that replacing it again would help...it may have been a failed attempt to fix it...or maybe it did fix it 15 years ago, only to fail due to a bad solder joint.

I looked around and the caps all look clean...all Rubycons, and no bulging, leaking or obviously loose ones. 

It's a nice system, overall.  At least it plays HuCards without any issues.

Let me know if you guys have any thoughts :-)

[thesteve]

look for any black traces or via's as they fail often
the system rom loads across the slot, so you can test the data there for a missing data bit (open pin?)
look for cda before the avc chip

[Yoder]

Excellent...thank you.  I googled and found that this is where audio mixing occurs and is behind the heatsinks.  I'll see if I'm getting a signal to and from it, and I'll make sure it's getting voltage.  Can you give me a hint on what to search on to find the data sheet?  I'm coming up with very little on this chip.

[thesteve]

for the AVC search the part number on the chip
I have a copy at home but not here.

[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!

/audioprobe.jpg

[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)