Need some electronics help!

[Ral-Clan]

Hi Amiga folks,

I am a long time Amiga user, but I am actually working on another electronics repair project that I need some advice on from the more experienced electronics people here on this forum.  It's actually similar to the capacitor replacement problem / battery damage problem Amigas have.

I'm fixing a 1992 (Amiga era!) Yamaha QY20 music sequencer.  I got it really cheap, but it doesn't function (I already knew this).  There is nothing on the display and there is a light hum through the headphones, but it is otherwise unresponsive.

I opened it up and noticed that a chip (labelled MAX680) was covered in white stuff and looks suspicious. There was white stuff around the chip and the legs seemed covered in white "fuzz" as well.  This seems to be a voltage converter chip.  The Yamaha service manual says it is a "MAX680CSA (XL660A00)".


(click on this photo to enlarge it)

On the opposite side of the circuit board, above it, are four capacitors.  They are all rated the same - they say "x2 22 16V" on them.  The service manual says these are electrolytic capacitors. These look okay, but I'm thinking they might have leaked and damaged the chip underneath (there are a few "through" solder holes nearby in the board where bad stuff could go through).


(click on this image to see a larger version)

So...I am going to try and replace all four capacitors and the chip.  I am actually a pretty good solderer and and have replaced fine components before when I had instructions to follow.....but I am NOT an electronics expert.  I can do the mechanical work of replacing the components, but have never bought components online before.

So this is where I need some help from the experts here.

1) Can anyone help me identify these components to make sure I am going to purchase the correct replacements?  I think the MAX 680 chip is this one:

http://www.futurlec.com/Maxim/MAX680.shtml

But I'm having trouble finding a source for the capactors.  I don't really know how to read the numbers printed on the capacitor and I don't know what specific type of capacitor I'm looking for.

2) Is there a reliable place to buy these components online?  Preferably one where I can buy individual components?  I have looked on Jameco, but I don't think I can get the chip I need there.  

There seems to be a lot of the MAX680 chips on eBay:
http://www.ebay.ca/sch/i.html?_from=R40&_trksid=m570.l2736&_nkw=max680

They all have the MAX680 number, but the code afterward is not CSA as on the original chip.  I'm not sure if this matters or not.

And I THINK this is the capacitor I want:
http://www.ebay.ca/sch/i.html?_from=R40&_trksid=m570.l2736&_nkw=22UF+16V+SMD+ALUMINUM+ELECTROLYTIC+CAPACITORS

Can anyone confirm I have the right products picked out?

Any other advice is welcome.

Thanks very much guys!

[odin]

:nervous:

I think dead components are the least of your worries if this is a multilayer board..

[Ral-Clan]

:nervous:

I think dead components are the least of your worries if this is a multilayer board..

Yeah, but it's worth putting a few bucks into it just to see if it will work.  I think it is not a multi-layer board, based on the service manual.  PS: I am fairly confident I can repair any damaged traces.

[Mizar]

The capacitor replacement problem is something I will have to deal with on my A1200, it sounds like.

Yeah, but it's worth putting a few bucks into it just to see if it will work.  I think it is not a multi-layer board, based on the service manual.  PS: I am fairly confident I can repair any damaged traces.

I am curious as to what your procedure is for repairing damaged traces.

[Damion]

The caps are 16v, 22uf. Looks like these would fit the bill, just make sure the dimensions are correct (just a guess judging by your pic). While I'm no expert, MZA series should be a safe replacement based on the specs, and I've used them on countless miggies (similar era tech) with great success.

Chances are the chips on ebay are fine, just do a bit of datasheet googling to be sure.

-edit- Missed your link to the caps on ebay. They might do, but I prefer the Japanese brands available through places like DigiKey for quality reasons... (don't want to do it again anytime soon!)

[TCMSLP]

Could you borrow an ESR meter from somewhere?  This would test the capacitors in-circuit and reveal if they're defective.  It could save you some work, unnecessarily swapping components.

I do remember seeing similar white stuff on a board before, but this had been stored in a damp environment and also had dead bugs involved.  I think the white fuzz was general corrosion mixed with tightly spun spiders web or some other form of insect coccoon/nesting thing.

I suspect in this situation you're correct though ...

[Ral-Clan]

I am curious as to what your procedure is for repairing damaged traces.

If it's a broken trace on the surface of a circuit board, you can take a fine copper wire filament (like from a pair of headphones).  Sometimes you might have to separate filaments in a multifilament wire and just use one strand (if it's a very fine trace).  Cut it to length to bridge the gap. You need to tin both ends of this.  Or if it's a very short "bridge" you can tin the whole length before you cut it off the original wire it came from.

Then you lightly scrape away the varnish/coating on the circuit board to expose some copper/gold trace on either side of the break. If you can tin this, it is good, but hard to do. If the tinning solder won't stick to the traces, you can try brushing some flux on these exposed areas.  The solder might stick then.

Next place the short bit of filament across the gap, with the ends touching the two exposed areas of the traces.  You might need to hold it down in the centre with something sticky so it doesn't roll or blow away.  Unfortunately, when working with pieces of wire this small, metal tweezers act as a heat-sink - so you cannot use them.

Touch the soldering iron to either end of the filament bridge and - HOPEFULLY - it will bond with the tinned exposed traces - repairing the break.

After testing with a multimeter to ensure continuity across the repaired trace, you can re-insulate the trace by "painting" the repaired area with clear nail polish or shellac.  Give it several coats.

That's it.  It's very tricky.

I've had success with this method with reasonably sized components.  i.e. 8-bit era stuff. When it gets extremely fine (like nowaday's electronics) it's obviously more difficult (sometimes very much so), but it's doable.  I also use a 5x and 10x jeweller's loupe.

[spirantho]

The Max680 you're looking at it is not correct. The one in the photo is SOIC, you're looking at DIP chips.

Do you have an SMT rework station? I use an Aoyue 8208 and it's cheap but awesome - I'd strongly recommend against too much SMT work with a soldering iron

[Ral-Clan]

The Max680 you're looking at it is not correct. The one in the photo is SOIC, you're looking at DIP chips.

Do you have an SMT rework station? I use an Aoyue 8208 and it's cheap but awesome - I'd strongly recommend against too much SMT work with a soldering iron

Thanks!  This is precisely the kind of blunder I was hoping to avoid.  Like I said, I can replace the parts without to much difficultly as long as I get some help identifying the correct part.  So I'm grateful.

Yes, I don't plan to replace any more than I've stated above - it's too difficult to attempt much more SMT work by hand.

[spirantho]

If you do like repairing stuff, though, still look at an Aoyue like mine. It's incredibly useful for removing through-hole DIP chips too from stubborn boards.

[Tenacious]

The corrosion looks like it is from water with the power ON.  You have probably already tried simply cleaning all of the corrosion with a fast drying, non-residue solvent and a tooth brush.  Try to work the bristles behind the pins and under the chip to get it all.  All of that fuzz may be conducting small currents between the pins of the chip that aren't supposed to be there.

If cleaning is not enough, I would definitely replace the chip first and wait and see about the capacitors.

[Ral-Clan]

The corrosion looks like it is from water with the power ON.  You have probably already tried simply cleaning all of the corrosion with a fast drying, non-residue solvent and a tooth brush.  Try to work the bristles behind the pins and under the chip to get it all.  All of that fuzz may be conducting small currents between the pins of the chip that aren't supposed to be there.

If cleaning is not enough, I would definitely replace the chip first and wait and see about the capacitors.

Thanks for the tip.  I do suspect that this electronic device has been exposed to water....perhaps a house flood.  There was a small amount of silt inside (not too much, just a trace) which make me suspect this.

I only paid $20 for this item, knowing it was dead - taking a gamble to see if I could fix it.

I did not realise that the crud on the circuit legs could conduct current.  I have cleaned it but I haven't tested it since.  I will have to do so.

[hairy]

hi ra-clan

as you may have guessed from the MAX680 datasheet, its purpose is to get dual power from +5V which is probably forwarded into op-amps and other analog circuitry.

Have you tried, referring to the pinout on the datasheet, to measure the +10V/-10V output from that chip using a multimeter?

IMHO the hum in the headphones seems to suggest that the power amp is not dead, have you tried the line output jack also?

After you finished with cleaning with a toothbrush, as someone already suggested, and rechecking the thing, if still no dice AND you feel brave enough, you could also attempt to temporarily feed +10V/-10V from some external power supply and at least have confirmation if the problem lies in that regulator chip.

P.S.: I have a working QY20, but it's one of the few lucky devices that escaped the "peek inside the belly" treatment :razz: So I can't say I know the circuitry very well. Also, samples from that specimen were used in the very first release of GMPlay.

[Ral-Clan]

Have you tried, referring to the pinout on the datasheet, to measure the +10V/-10V output from that chip using a multimeter?

Here's where (embarassingly) I have to profess my ignorance.  While I am a fairly good soldering and tinkering, and have repaired electronics and swapped parts where I had instructions, I am not an electronics expert (only knowing what I have learned myself).  I have a multimeter (a decent one) but I do not know how to conduct the measurement as described above.  Could you give me a step-by-step?

Am I correct in that, with the device powered on, I would touch one multi-meter probe to the circuit leg, and the other to ground to test if the proper voltage is coming out of that leg?  The multimeter would be set to measure DV voltage.  Is this correct?

That's fascinating to hear the QY20's samples were used in GMPlay for the Amiga - great Amiga connection!

I appreciate all the help I am getting on from members contributing to this thread!

[hairy]

Am I correct in that, with the device powered on, I would touch one multi-meter probe to the circuit leg, and the other to ground to test if the proper voltage is coming out of that leg?  The multimeter would be set to measure DV voltage.  Is this correct?

Yes, that's correct.

Unless your multimeter is NOT a digital one, don't worry too much about range and polarity, it will simple display opposite sign or display over voltage. Nevertheless, try to use the black probe on GND and the red one on V+ and V- pins. Mine has ranges like 200mv, 2V, 20V, etc., in this case the correct range would be 20V. Just choose the first available range that's higher than the voltage you're going to measure.

Just looked at the datasheet again, we're lucky since all three pins are located on three corners, this way even if the chip is SO package, it should be farly easy to push probes over the pins from the respective outer side, without the risk of making shorts.

This is the complete pinout:

1 C1-
2 C2+
3 C2-
4 V-     <= red probe here should read something near -10
5 GND   <= black probe here for both measures
6 Vcc
7 C1+
8 V+     <= red probe here should read something near +10

The line on the chip is the "front" of it. Looking toward the front, pin 1 is the top-left one, pin 4 the bottom-left, 5 bottom-right, and 8 top-right.

Sorry if it's a bit pedantic, but at least I hope it's understandable!