X68000 compact low volume on pcm sound but music ok.

[gypsie]

Hello,

I ve replaced all caps on x68000 compact motherboard. Work fine but now the sounds effects have low volume (music sound volume is good). Ingame, i can't hear sounds effects because music volume is too high.

I ve checked all capacitors => ok (solder and polarity)

Do you think that IC7 amp must be remplaced?

[eidis]

 Hi Gypsie !

It is most probably related to bad op-amp or a broken trace. More info here:

X68000 XVI Compact audio troubleshooting and repair
http://gamesx.com/wiki/doku.php?id=x68000:x68000_xvi_compact_audio_troubleshooting_and_repair

Need information about C1 SUB capacitor. Can someone confirm that it is  a 0,47UF 50V ?

Pic please.

Keep the scene alive !
Eidis

[gypsie]

It looks like that sub C1 is 0,47uf 50v .

I will edit the topic...

[emerald danjon]

Remember a compact i was having in the past,same problem,Music OK,
but no Sounds...,i was Refurbished all PCB and no luck.
i hope you can Fix,
better wishes.

[gypsie]

Remember a compact i was having in the past,same problem,Music OK,
but no Sounds...,i was Refurbished all PCB and no luck.
i hope you can Fix,
better wishes.

There are sounds but volume is too low...

[eidis]

Hi Gypsie !

Do you think that IC7 amp must be remplaced?

Lydux has made an awesome troubleshooter for compact audio problems which I mentioned in my previous post. I suggest that you read it thoroughly and try following it step by step. Start by searching for broken traces. There are even pictures in the guide which show the most common places for failure. The trace might not look broken so it is necessary to do a continuity test. If that does not help, replace op-amps.

X68000 XVI Compact audio troubleshooting and repair
http://gamesx.com/wiki/doku.php?id=x68000:x68000_xvi_compact_audio_troubleshooting_and_repair

Keep the scene alive !
Eidis

[emerald danjon]

I don't Know if this is what in my Compact was the reason for lost the sounds...,but when i try to do the refurbished...,i remember broke a lot of tracks.
the Corrosion of some SMD capacitors was terrible,and with this Computer never was sure about if the problem was mine...for my bad Refurbished or for other reason.
with the Refurbished i only got return the music but never the sounds,pity.

[eidis]

 Hi Gillianx68000 !

The majority of compacts, with time, suffer from broken traces near the op-amps. The pictures with red circles will give you hints where to look.

X68000 XVI Compact audio troubleshooting and repair
http://gamesx.com/wiki/doku.php?id=x68000:x68000_xvi_compact_audio_troubleshooting_and_repair

Keep the scene alive !
Eidis

[gypsie]

Gillianx68000, did you replace AMP  MC 3403D on IC39 et iC7 ?

[emerald danjon]

No Gypsy...,one good friend bought me the computer...,cheap...in a really bad Shape...,one FDD not Working and the problem of the Sounds.

[gypsie]

This computer will make me crazy! 

I ve changed amplifier MC3403D on IC7 with a new MC3403D.

Sadly sounds effects volume is the same ( too low) AND NOW after 15 seconds, sound and music disappear!!!!!!!

I don't understand what's wrong I will remove the new Mc3403 and put the old one back.

[eidis]

 Hi Gypsie !

I don't understand what's wrong I will remove the new Mc3403 and put the old one back.

Wait ! Not yet.

If the sound is coming out distorted or at a very low volume, the first thing you can try is replacing all capacitors.

Did you recap the board ?

Keep the scene alive !
Eidis

[gypsie]

Yes all capacitors changed...

[emerald danjon]

  sure not track broken?,
try look at the light...sunlight directly...,maybe have a track Broken,
SMD capacitors...Grrrrrrrrrrrrrr.

[eidis]

 Hi Gypsie !

Try inspecting the tracks near capacitors and exposed copper spots for continuity. This will be a fetish torture.

Keep the scene alive !
Eidis

[gypsie]

Hi,

Picture of the faulty new MC3403D :




I ve removed the new MC3403D and put the old back, ( sound+music are like before but always low volume on sound effects).

Perhaps the new Mc3403D wasn't compatible? Very strange. Please look at the picture (old to the left)





I ve remade with solder test points near IC39 :



My full recapited mother board :

[eidis]

 Hi Gypsie !

Rust is able to accumulate under the solder mask and corrode the traces underneath it and it is impossible to tell by using a naked eye if the traces are good or not. You will need to examine them with a continuity test. I suspect that the broken trace could be next to one of those solder pads to which the new capacitors are soldered. Start by checking the traces betwean each output pin of YM3012 DAC and the op-amp.

Keep the scene alive !
Eidis

[H68k]

At first I thought this was a quirk with the Compact models, but after reading this.. it would appear my own Compact is suffering from the same problem. (ADPCM is quieter than the FM etc)

This will be a fetish torture.

With all the crap I've had to go through so far with my X68000's... I may as well put on some S&M gear and hand them a whip!

[gypsie]

I do you change all capacitors on main board?

[X-Col]

At first I thought this was a quirk with the Compact models, but after reading this.. it would appear my own Compact is suffering from the same problem. (ADPCM is quieter than the FM etc)

This will be a fetish torture.

With all the crap I've had to go through so far with my X68000's... I may as well put on some S&M gear and hand them a whip!

Any good games for checking this on my Compact? I feel your pain mate, I'm still working on my Ace and I started that repair last September! On the home stretch now though with only a capacitor change to do on the floppies...

[caius]

First of all, PCM sounds are generated by the OKI6258 chip.So, you could proceed in this way to test it: connect the Digital to Analog output of this chip to an external AMP to see if sound come out properly (or use an oscilloscope to analyze the signal).This si the datasheet of the MSM6258:


http://pdf.datasheetarchive.com/datasheetsmain/Datasheets-112/DSAP0054035.pdf

'DAOUT'   (the digital-to-analog output) is pin 15   so connect it to an external amp (obviosuly you need also a  GROUND signal ).In my arcade repair I use a simple cable with an 3.5" femal jack at one end connected to my hi-fi system.
I've repaired a lot of arcade boards with bad MSM6295 ADPCM chip so this could be the culprit also in your case (chip is different but same manifacturer)

[miisalo]

Sorry for resurrecting old thread, but I have exactly the same problem with x68000 compact. First just a note about Caius post, its pin 22 that is DAOUT, you are looking at standalone version, not the CPU version that is used with compact.

In the beginning I didn't have any pcm sound so I recapped all the electrolytic caps and actually also replaced the PSU with picoPSU (to get rid of stepdown converter as we have 230-240V here). I couldn't get the 0.47uF smd caps so I replaced everything else without much success. Then I started to check the schematics from 68030 service manual and tracking the traces to understand which are the corresponding components in the x68000. I noticed that 0.47uFs are mostly used as DC filtering in the PCM signal and replacing the C9 that is used to filter DC components from signal just after the IC 7 op amp was the BINGO moment: I got the PCM back.

Problem is that it is maybe half of the volume compared to FM, at least in the bomberman I'm using to test it. I did replace all the other 0.47uF caps too but they didn't have any effect.

The thing is that I have scoped the signal and it looks like it comes out from the chip like VPP over 1V, goes through the DC filtering (ADPCM PWB board) still having nice VPP, goes to the series of resistors and ground connecting ceramic caps and arrives to the OP AMP having VPP about 200mV. First stage through the OPAMP is just buffering (inverted input has feedback from the output without resistor) and the signal comes out with same VPP as expected. Then it is combined with FM signal that has about twice of the VPP and is amplified.

So either the signal from the MSM6258 should have even higher VPP or the signal is dampen too much before opamp. Or I'm missing something, that is very possible.

Maybe I need to scope the signal as DC to see if there is something wrong with dc biasing.

[miisalo]

Jump wiring adpcm pwb's out signal directly to IC 7 brings up the PCM volume quite well. I might even settle to this dirty fix...

[caius]

Sorry for resurrecting old thread, but I have exactly the same problem with x68000 compact. First just a note about Caius post, its pin 22 that is DAOUT, you are looking at standalone version, not the CPU version that is used with compact.

I didn't know which version of the OKI6258 DAC the CompactXVI actually  use so I generically indicated the standalone version just to make you all to understand which was the DAOUT pin to check.
About your problem, check for corroded track or via, it seems you are missing some signal (GND perhaps)

[miisalo]

No problems with traces or vias. It was first thing I checked. Audio path, both FM and PCM seems to be ok.

Anyway, I had to take out the transistors Q20 and Q21 that pull down the pcm( when no sample is playing) just before mixing it with FM. They made dc bias of the signal slowly change resulting to cracking noise when grounded by the transistor after sample ended. Now the bias stays where it should. What I have read, its not uncommon them to fail.

What comes to the audio level, the actual audio out seems to be out of specs, too loud! Which means that actually the FM volume is too high. I did use very low esr caps but they are paired with resistors in the circuit so tiny change in the resistance does not explain it. So my dirty solution to fix the sound is not amplify the PCM more but changing the R27 and R31 resistors for the FM just before mixing/amplifying stage from 3.3K to 6.7K. That will bring down the FM levels and balance them with PCM.

XVI Compact uses almost the same schematics as the 68030 compact except it uses dc biased signal and op amps are  using single supply (+VCC and GND) whereas 68030 version uses dual supply (+VCC and -VCC ). And there is that ADPCM PWB.

In 68030 schema the Q20 = Q23, Q21 = Q24, R27 = R15 and R31 = R24

[PepAlacant]

I had the same problem with a Compact XVI. I replaced the OP-AMP, it worked for a few time and the problem reappeared with clicks on the PCM sound. I really hate the Compact model... I finally sold it and got a normal XVI.

[X-Col]

Anyway, I had to take out the transistors Q20 and Q21 that pull down the pcm( when no sample is playing) just before mixing it with FM. They made dc bias of the signal slowly change resulting to cracking noise when grounded by the transistor after sample ended. Now the bias stays where it should. What I have read, its not uncommon them to fail.

Apologies for the necrobump, but I'm experiencing this 'Cracking' phenomenon on my XVI Compact. It starts about 5 minutes after a cold start.

I found this thread and think I have the same problem as miisalo. How does removing the above mentioned transistors resolve the problem of DC Bias? Surely they perform some important function? If they have failed, I would rather replace them.

Or, is this a design flaw in the Compact model and removing these transistors is the correction?

[X-Col]

Ok, I bit the bullet and opened up my Compact, again!

Removed Transistors Q20 & Q21.

I'm glad to report that this does in fact cure the problem!

I note that the area around the 2 transistors was very corroded and a strong fishy smell followed. Must be a capacitor leakage that caused the transistor failures. It was so corroded that I lost both base solder pads in the process of removal.

I do know where to jumper them if necessary, so my question is: should I buy new replacements and fit them?
I'm guessing that they are there for a reason 

[kamiboy]

Of course you should. Resistors cost next to nothing, no reason not to.

[X-Col]

Of course you should. Resistors cost next to nothing, no reason not to.

They are transistors, 2x DTC114EK. I agree, so ordered replacements as they mute the PCM when no sample is playing. Not exactly cheap these things, cost £5.88 

Regarding the balance of FM/PCM on the Compact, mine has a better balance than my ACE.

I think the failure of these transistors, which leads to clicking/cracking of PCM, is quite common and should be added to the Wiki.

[kamiboy]

Wow, 6 pounds is quite a lot for transistors. A search on eBay revealed no Chinese sellers of that particular type, so I guess it is not a common part which explains the price.

I believe anyone can edit the wiki, so you can go ahead and add it yourself.

[X-Col]

@kamiboy

yes it is expensive for 2 transistors, but worth it to finally fix everything in this Compact.

Fitted them both and all is good, sounds perfect! 
Without them there is a high pitch background noise.

Everything now working as it should, including the 2 floppy drives! 

Regarding the Wiki, I have no clue how to do that. I would also add that the opp amps in the XVI Compact are +5V & Ground, not +12V & -12V as I was lead to believe. This info caused me a lot of trouble... 

[leonk]

Including the 2 floppy drives!? How did you do that???

I gave up fixing mine and using FDX68 instead.

[X-Col]

@leonk

Just tinkering with them for 4 years, pure stubborn persistence. They've been dismantled, cleaned, recapped, aligned; several times.

The only thing is the short ribbon cable is a bit knackered now because they have been connected/disconnected so many times. 3 of the metal traces have come away from the plastic, so I could do with a replacement.  Seems these things, like so many other parts of the machine, are non standard 

Anyway, if I'm careful, it goes back in and still works 

[toyhopperhk]

Hello
I cant find C1 sub 0.47uf,where is it?
Can show me the pic?
Thx