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TheCorfiot
8th April 2009, 16:46
Hi Guy's n Girl's

Took my Head out of my A4000 today & carried out capacitor replacement for Scrappyshinx's A3640 CPU Board.

As many may have heard me say before these boards suffer from an incorrect silk screen layout & the Capacitors C105,C106 & C107 are inserted the wrong way round.
This does lead to shortening the cards life & the capacitors leak nasty PCB eating acid...

SS's CPU board was already missing C106, continuity tests proved the remaining two capacitors were indeed incorrectly polarised.
OK Removal time, as soon as my Iron touched the legs of one of the caps the unmistakable smell of acid erupted......euch

Consequently further examination revealed that 3 pads had been all but been consumed, acid spillage had travelled to nearby chips too.
There was no other way but to clean out the relevent pinholes (filled with gunk from the acid) & attempt to fit conventional capacitors in place in order to save the card.
After carefull soldering & using sticky foam pad to secure the caps, success :D
C106 was replaced with an SMD cap of course as it's pads were fine.

Now the Board was fully cleaned up, continuity tests proved all capacitors were in circuit and active.

I then fitted the board to my A4000 (god I thought I wasn't touching it today!!!) & ran the board for 1 hour proving fault free & stable operation...Sysinfo also reported & performed as it should. !!!!

Another A3640 saved from the Tip and not a moment too soon by the look of it !!!!!!! :lol:

TC :mrgreen:

SkydivinGirl
8th April 2009, 17:47
Excellent work TC! It is wonderful that we have so many knowledgeable users on AmiBay and that they are willing to help each other out!

Hmm... My A4000 has an '040 card. I'll have to check if it is the A3640. If so, I may have to do some repair myself. :(

Heather

keropi
8th April 2009, 20:11
do you have more than 16MB fastram SkydivinGirl ? If not then 99.9% chance you have the A3640 cpu card :wink:

SkydivinGirl
8th April 2009, 20:13
Nope, I have 16MB exactly. I'll be checking out which card I have tonight when I get home from work.

Thanks!

Heather

scrappysphinx
8th April 2009, 22:11
The repairs look fantastic and i cannot thank TC enough for even attempting the repair never mind achieving such fantastic results. TC has just saved me a fortune in repair or replacment bill!
Thanks my friend

Mike

TheCorfiot
8th April 2009, 22:33
Your very welcome Mike

I'm thinking of starting up a PCB / Amiga repair service in Wales, What do you guy's think? :D

@Heather

More than likely you do have an A3640 card my girl, now if you have access to a multimeter I can PM you step by step instructions to test your board & confirm if the Caps are correctly fitted.

Do let me know if I can help :wink:

TC 8)

arnljot
9th April 2009, 00:31
I'm thinking of starting up a PCB / Amiga repair service in Wales, What do you guy's think? :D

Great idea! :)

imnogeek
9th April 2009, 00:50
I'm thinking of starting up a PCB / Amiga repair service in Wales, What do you guy's think?

Good idea, now I've just picked up a lappy which needs soldering..... :D

PhilipMcD
9th April 2009, 11:53
Glad this thing has finally been sorted for Scrappysphinx. When I had it I just fell back on the A3630 instead, and it sounds like a good move I did do because this thing may have been dead by now? Who knows.

I wouldn't have had the slightest clue how to rectify those issues.

Good work TC!

SkydivinGirl
9th April 2009, 14:15
@TC

I would love to get the directions for testing the capacitors. My soldering skills are good enough to replace a couple capacitors.

Thank you!!!!

Heather

davideo
9th April 2009, 15:37
I'm thinking of starting up a PCB / Amiga repair service in Wales, What do you guy's think? :D

Do you secretly work for AmigaKit :lol:

They've just recently started to offer loads of repairs, i.e. ram slots on 4000, even caps I believe.

Dave G 8)

rkauer
9th April 2009, 15:57
@SDG:

Simply following the +5V and GND lines will show you where the right connection must be.

A tip: on all TTL chips, the farthest pin on the pin #1 side is always GND. Last pin is +Vcc (5V).

For what? Good spot to locate the power supply rails! :wink:

scrappysphinx
17th April 2009, 19:57
Hey all, i finally got round to installing in the A3640 that TC excellently repaired for me.
I have to say it was a fanastic service by TC, with the card repaired and recieved back within a week.
And guess what, The A3640 is performing perfectly.
Not only did he repair this board for me, he also repaired an Xbox motherboard which i screwed up by removing an smd resistor while attempting a mod. He repaired the missing resistor and performed the mod so i could continue along nicely.
I'm sure he won't mind me posting this pic of the xbox motherboard to show off his awesome work again.

[attachment=0:12jdlwyc]DSC00001.JPG[/attachment:12jdlwyc]

I cannot thank TC for his very kind gesture or attempting the repair on either of the boards and pulling off the fantastic results.
I can highly recommend him for any repair work and i would welcome a repair service should he decide to start one.

Thanks again TC

Mike

TheCorfiot
17th April 2009, 21:34
Thanks for the kind words Mike It was a real pleasure to help such a nice guy. :wink:

The Xbox mod was certainly tricky as tracking needed for the "link" to enable re-programming was also gone, but by studying some pictures I understood that the 2 pin holes could be joined & pulled to ground via a 10K resistor which would have the same effect.

So Glad it all worked out.

Also finally fixed the "World Tour" DCE Scandoubler of Mike's, problem was due to a broken track connected to the H-Sync Ribbon cable header.
Poor design really as the pins in the header were free to move, the plastic enclosure did not offer any support so everytime the plug was inserted pressure was put on the solder track joint on the PCB.

I replaced the Pin Header with a durable type & cleaned & re-soldered the whole board whilst repairing the track with a thread of copper, also replaced the VGA connector as the contacts were also quite worn.....
Works an absolute treat now, stable & clean image... :mrgreen:

Thanks again Mike, If any one needs any repairs let me know... :wink:

TC :mrgreen:

Hessu
17th April 2009, 22:56
Where can i find a replacement for RCA connectors on my Delfina lite soundcard? Those are a quite worn out, left channel is off, but if i move the wire a bit then it's on, resoldered traces, but didn't help, so it has to be the RCA connector itself.

Fine work you have done, i have a spare A3640 rev.3.0, removed the capacitors too, and those contact plates didn't survive, and i thought it's a goner :) Luckily enough, i didn't throw it away, it might be repairable still :)

Polymorph
2nd May 2009, 21:17
Hi Guy's n Girl's

Took my Head out of my A4000 today & carried out capacitor replacement for Scrappyshinx's A3640 CPU Board.

As many may have heard me say before these boards suffer from an incorrect silk screen layout & the Capacitors C105,C106 & C107 are inserted the wrong way round.
This does lead to shortening the cards life & the capacitors leak nasty PCB eating acid...

SS's CPU board was already missing C106, continuity tests proved the remaining two capacitors were indeed incorrectly polarised.

In your photo, C106 is there, but I notice it is in backwards.

Someone asked how to tell if the capacitors on their boards are the correct way round.

The black bar on one side is the negative lead. Also notice that the base looks like a rectangle with two corners clipped, that is the positive lead.

If you look on the PCB, you can see that shape in the silkscreen, and a "+" printed near that side. If the black bar isn't opposite that, your caps are backwards.
http://img.inkfrog.com/pix/echo242372/4_7uF_63V_SMT_Electrolytic_Capacitors_Kit.jpg

BTW, as electrolytic caps age, even when installed correctly, the ESR goes up. The capacitance if measured out of circuit may still read within tolerance, but increased ESR may still make the circuit operate incorrectly. Fortunately it is fairly simple to build or buy an ESR meter, and they can test aluminum electrolytics in circuit.

arnljot
2nd May 2009, 21:27
If you look on the PCB, you can see that shape in the silkscreen, and a "+" printed near that side. If the black bar isn't opposite that, your caps are backwards.

Vigilant eye! :)

Infact the silkscreen on this card is misprinted. It's a well known fix and one of the things going on in this thread :)

TheCorfiot
2nd May 2009, 22:43
@Polymorph

Thanks for the feedback, Unfortunately this is the big issue with these cards that the silk screen is incorrect but the capacitors were installed as per the silk screen during manufacture and consequently leak over time as they are incorrectly polarised.

The simple test is to carry a continuity check between the Crystal Body (GND - 0V) & each capacitor pad, this then reveals the board error.

I can 100% confirm MIke (Scrappy), there is no need to worry the Caps I fitted are the Right way round.
My own A3640 was exactly the same..

Some revision CD32 Motherboards also have this issue regarding the main filter capacitors, & boy do these swell up :nod:

TC :thumbsup:

Polymorph
2nd May 2009, 23:17
Ah... didn't know that. What a pain.

Continuity check to a known ground is a good way to check for polarity, since I don't think there are any negative supply voltages on that board. Are there?

arnljot
2nd May 2009, 23:20
Details can be found on this excellent (http://amiga.serveftp.net/A3640_capacitor.html) site :-)