XVI Compact FM audio is low volume and distorted. (Fixed!!)

[Maxwar]

Hello, first time posting here but been reading a bunch on this forum

I just bought my first X68000, a XVI compact and it has the same symptoms described in this thread ( low and distorted FM)
http://nfggames.com/forum2/index.php?topic=4728.0

Hopefully i can repair it thanks to all the amazing work that has been done here.

I just finished taking the computer apart and made some initial checkups. I checked the voltage on the opamps and i get 5v at the Vcc for both IC39 and IC7 opamps and about 2.5v on other pins of both amps, so this is different from Robivy64's initial reading of very low voltages on IC39
I tested around for broken traces but did not find any so far, i checked the traces specified in the Flowchart around IC39.

Talking of the wiki flowchart: http://www.gamesx.com/wiki/doku.php?id=x68000:x68000_xvi_compact_audio_troubleshooting_and_repair
Would just like to point at a very minor detail in the wiki flowchart. It seems to me the Pin 7  of IC39 is connected to the + of C29 rather than C28. Typo?

(Compact models only) Using an ohmmeter, x68k powered off, check for resistivity between pin 13 of IC39 and + pin of C31. Do as well between pin 7 of IC39 and + pin of C28. The indicated value should be < 100 ohm. If more or open circuit, the 2 test points near to IC7 pins starting to get corroded (see picture), and need to be cleaned. Soldering a simple wire between involded pins will also do the job.

Furthermore  Im a little dumbfounded as the wiki intro says:

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

But lower in the Lydux flowchart it is recommended to change both op amps and some Transistors before going for the caps.
Somehow i would have thought of going for a recap first, no?

Im  only a hobbyist and not at all an expert on electronics but ive done quite some soldering and recapping on various stuff already so hopefully i can get through this.
Anyway, any advice is welcome on this repair project,
Will try to keep this updated with my progress.
Thanks in advance.  

[BlueBMW]

Personally, I recommend doing the caps before anything else.  Both on the mainboard and the Power supply.  At this age, they're definitely leaking / failing.  Replace them and clean the board really well (soap + water, then dry for a few days) 

After doing caps, check those points described around the amp chips and make sure you dont have any opens or corroded traces.

Good luck!

[Maxwar]

Thanks for the reply!

Im going to start preparing an order on Digikey and get all the parts for a full recap.

What kind of caps would you recommend?
In the other FM audio thread regular through hole caps were used instead of SMD.
I somewhat feel inclined to respect the original concept and use SMD caps here though.
I used Nichicon HM,HN or HE when i previously recapped PC motherboards but those are only made in through holes soldering.

I was looking at the Nichicon WF low impedance series but Digikey does not appear to carry them. They have the WT series though which is more "general purpose " . Otherwise i might be taking a look at some Panasonic models.
Also, using SMD caps here would mean that i have to measure all the base Diameters to make sure the new caps fit the original size.

Any thought on the subject ?

[BlueBMW]

Personally I use mid to upper series Panasonic leaded caps to replace the SMD ones.   They give you flexibility in the event that a pad lifts from the board and theyre easier to install.  Functionally they make no difference.  I think people will respect the fact that your 68000 is fully operational more than whether you used original style caps or not

Theres enough room for cut leaded caps to be used so space isnt a restriction.

Good luck and keep us updated!

[Maxwar]

I ended up ordering leaded caps, i had not realized how much solder was underneath the SMD caps, i think it would have been quite difficult to install them with only a soldering iron. ( I dont have hot air station )

My only worry is that some of the caps were "back order" on Digikey. Last time I had BO items I did not have to wait long but this could be different and i dont feel like waiting a month for my caps...  

In the meantime ill remove all old caps from the boards. I found out that by using cutting tweezers and wiggling the SMD caps a little they come right off their pins with surprisingly little force, then each pin can be unsoldered separately, this seems to be a very safe method.

Will keep this updated!

Edit: I could not bear the doubt, called Digikey and yeah, there was over a month of expected lead time before they had stock for some of my parts so I cancelled the order and Remade it with no B.O this time, I switched from Nichicon to Panasonic and Added a 3v Lithium battery. I should have my parts next week if all goes well  

Most Caps "look" fine on my board but C31 DEFINITELY leaked. I dont see a broken trace but that cap was busted and the pads are all oxidized. That might just be the culprit right there. Anyway im still aiming for a full recap.

[BlueBMW]

Yeah once you see one leaking cap you can bet they're all starting to leak!

I use some nippers to grab the cap and wiggle / twist it til it breaks off.  Then I go back, cut whatever is left of the legs and remove the plastic bases.  Then I dab some flux on each pad and go back with my iron and remove the bottom part of the cap leg thats still on the pad.   Finally, I use some desolder braid to remove all the old solder (and you can kind of use the braid to scrub the cap pad to remove any nasties)  Finally I wash the board really well and dry.  Then recap

A little extra effort cleaning / preparing now will help make your repair a long term one

Good luck!

[Maxwar]

All the removing and cleaning is done on the board. Everything went well so far. Waiting for the replacement parts now.

After i was done cleaning i checked again for broken traces with the continuity meter. Did not find any, all looks good. Hope all goes well after the recap. 

[Maxwar]

OMG IT WORKED!! 

After a full motherboard recap my FM sound is back!! I let the Alien syndrome Demo play for a minute and both FM and PCM sound appear all right.
I still have to recap the floppy drives and the PSU but that will wait till tomorrow, its kinda late now.

Wow im a happy geek right now, ill celebrate with a cold one. Will post some picture of my recapped motherboard a bit later.

Thank you BlueBMW, thank you nfggames!!

[BlueBMW]

Glad to hear!

In my opinion, if your floppy drives are working good Id leave them alone.

But be sure to recap your power supply soon!

[Maxwar]

I recapped the PSU and started putting the machine back together. Problem is im still having an issue with the floppy drives. Drive 01 will sometimes stop working for no apparent reason. When this happens a floppy often gets stuck in the drive and i have to wait and reboot the machine later to be able to eject the disk.

I guess i will have to recap the floppy drives too 

[BlueBMW]

Ive have a pair of compact floppies that does that... its like they just randomly power off evem though the power supply is good.   Hopefully a recap will fix yours!

[caius]

Yes, I can confirm that a recap should solve this problem, some time ago I succesfully made it.In addition check the condition of the flat cables which connect motherboard to FDDs.

[Maxwar]

I took the floppy appart, wow those things are delicate, i see why you recommend not messing with them if you dont have too. 

I used long nose pliers to carefully disconnect that paper thin ribbon and all went well.
I will do the recap later today, sure enough the solder pads look all crusted and dirty, I think those caps leaked.

Hopefully reassembly of the floppy will go as well as  the taking appart. Would be a utter shame to screw something up at this point.

My FDD-Motherboard ribbon cable is ok i guess but it sort of got stuck one time and i had to pull quite hard on it. Turns out one of the tiny metal teeth had started to foil over itself. As a result of using force there is a small stretch mark on the side of the ribbon. The trace inside does not look like it has been affected but i checked with a multimeter to be sure, it tests all right but those ribbons are obviously not made for repeated inserting and removal. Hope the next time i connect it will just all work and i can leave it like that.

Just in case can these type of ribbon cables be purchased  from electronic suppliers?

Thanks alot for the support so far!

[caius]

I searched those flat cables everywhere but never found them.I presume they can be purchased from some manifacturers only in great quantity

[Maxwar]

It is done guys, every single electrolytic cap in this machine has been replaced. With the old caps went away all the problems. Everything is working great now. Sound is perfect and the floppy drives just keep working.

This is the biggest recapping job ive ever done so far, happy with the result. I also replaced the PSU fan as the old one was noisy and was showing sings of weakness.

I took some pictures  of the recapped motherboard and of the finalized system. Glad this forum was here to help me with this repair. THANKS A BUNCH!! Ill stick around!

[BlueBMW]

Ahh, always love to see another system brought back!  Have fun with it!