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Viewing 1 to (8 Total) PR903 not starting |
Hungary
Total Posts: 7
Joined: May 20, 2018
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Hey folks!
I got my hands on a dead SX-PR903 for chump change (shipping it cost more hehh), expecting a blown powersupply or somesuch, but it looks like I got hosed on this one. Power rails from PSU are OK, 5v, 3.3v rails all seem to check out fine even within the main board. (There are some things that are a bit out of spec, like 3.3V rail is about 3.2V, and somewhere one of the 'sub' 5v rails reads around 4.82V, but that shouldn't really be a problem.)
I started poking around a bit with my scope, but as it happens, I am getting erratic results. Sometimes the reset signal will dip rythmically about twice a second, then stays solid high, sometimes it stays on solid from the get-go. Poking at the IOs of the flash at IC11, I mostly just get a burst of data transfer, then silence, or occasionally one pin or another gets stuck in a repetitive pattern. So I'm a bit stumped here... I read these boards have lots of surface mount problems, but I don't see anything like that, and there is no change in behaviour if the board is flexed at all.
Can anyone give me a tip on how to go about this? Or is it best if I just reflow all the SMD components and see what happens?
Thanks for any help!
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Posted on May 20, 2018 at 9:28 PM
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Hungary
Total Posts: 7
Joined: May 20, 2018
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Re: PR903 not starting
So after reading through the service manual, I actually have more questions. Though I'm a service tech, I never dealt with the CPU side of any of my Technics instruments before (okay a PX103 but patching up corroded tracks ain't anything special).
From what I understand, the actual operating system is loaded into the flash at IC11. If this chip, or it's contents are corrupted/erased, should I still be able to get the diagnostic pages going with c#3 d#3 c#4? (If not, what is the point of the IC11 self-check in the diagnostic anyways...) Also, if I try to start the "update system menu" with the panel buttons 1234, again there is nothing happening. Would I need to actually have the required floppy disk in the drive to get this to start? Does anyone happen to have the update diskettes or their data and how to format them?
I'm suspecting IC11 or one or both of the RAM chips at IC8/IC15, but no way to test them really. I'm no fan of reflowing random components, but at this point good quality flux and a small iron are my last resort.
If it still refuses to come up, can someone point me in the right direction as to who can fix this board in an affordable budget?
Posted on May 21, 2018 at 10:52 AM
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Hungary
Total Posts: 7
Joined: May 20, 2018
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Re: PR903 not starting
Just to update, yes this is indeed an SMD problem. Since it was not booting intermittently I was fairly certain I had a problem with an actual chip and not delaminating chips, but once I got the board out and flexed it lightly, It was now warm, so I noticed the clicking sound coming from under IC11. Obviously the glue that was used to fix it onto the pcb before soldering had let loose, so it was a good candidate it might have cracked joints. So since I got out ma iron and the good flux, I went ahead and reflowed IC11,8,15 and 2. I still heard light cracling indicating loose legs, so I did IC301 as well. Since I now heard barely any crackling when I flexed the board lightly, I went ahead and gave it a try. And to quote Frankeinstein... IT'S ALIIIIIIVE! 
Well... mostly... display is still blank, but everything else seems to work. I will go back and check on the display driver chip, that might be the source of the remaining little crackle, so hopefully it'll bring the display back to life too, and then I'm in business.
Posted on May 21, 2018 at 2:35 PM
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Hungary
Total Posts: 7
Joined: May 20, 2018
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Re: PR903 not starting
Not sure how the CPU itself is supposed to work, but it was not even outputting the bus-clock for the lcd driver (and I checked with a scope on the output pin of the cpu). Nevertheless, after warming up I started having erratic behavior, so went over pretty much all the larger chips with fresh leaded solder, and now I have display. Everything seems to be functional too, just... no sound... but at least now I know everything should be functional once I get all the dead solder out.
Posted on May 21, 2018 at 5:05 PM
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United Kingdom
Total Posts: 360
Joined: June 8, 2014
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Re: PR903 not starting
Hi, and thanks for keeping us up to date with your project. I admire your determination in finding and correcting the faults. I think it is more than a little challenging, one fault I have come across Is the connectors that have plug-in ribbon type connection. The main problem is tarnishing that has built upon the contact so you get either no connection or intermittent operation. Please keep us up to date on your progress and on behalf of the site may I wish you well and good luck.
Regards John Dawson.
Posted on May 21, 2018 at 9:26 PM
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Hungary
Total Posts: 7
Joined: May 20, 2018
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Re: PR903 not starting
Thanks for the info, though I don't think there's a fault like that here, it came from a warm home, so luckily there's no corrosion whatsoever on the connectors, and even the backup cap has been replaced at one point, the previous owner clearly cared for it.
I have a PR902 that had the cabinet literally smashed to bits at one point, so it's an ugly duckling, but I love the versatility, and it does have some really sweet sounds. So I grabbed this 903 with a "if it's a non-fixer, I'll transplant the 902 into it" mindset (hell I thought I'd have a spare display for the 902 at least, only to find out the 903 doesn't have the colour lcd... which is ... odd?), but I'd really love to get this guy going now that I know that it's actually fixable. The problem is that now I'm sure I'll need to find someone with a proper rework station who can remove and re-mount the chips one by one, as whenever I reflow a chip, I fix something, but break something else. At one point I had everything working, only to, about 15 minutes in, have the audio go crazy amidst a loud crackle. An old phone modem has nothing on a DA converter that gets garbled input. lol 
So then I reflowed the DSP and sound generator, only to then have the os start locking up again... reflowed the progam rom and ram again, then I got garbled audio again, fixed that, then the display went again... and right now I'm back to non-booting... :\ Heck I won't mind paying for someone with pro equipment to do this job properly for me as long as it's done right.
Posted on May 21, 2018 at 9:47 PM
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Hungary
Total Posts: 7
Joined: May 20, 2018
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Re: PR903 not starting
So following a tip I got, I reflowed all the larger chips whilst applying pressure to their top. This definitely helped, as I got the thing working perfectly, but only for about 20 minutes... then it started making noises instead of sound, then finally crashed, and we're back to intermittent booting... it is starting to get on my nerves...
Posted on May 22, 2018 at 7:39 PM
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Hungary
Total Posts: 7
Joined: May 20, 2018
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Re: PR903 not starting
So... I f***** up... Apparently I did not notice a blob of solder somewhere shorting the 3.3v rail... I will take this board to an acquaintance who has pro SMD soldering gear, but I want to fix the 3.3v rail first. Does anyone have a source or alternatives for the following parts:
1xD201 MA2051LF
1xQ201 2SB952A
1xD202 MA2QD0100L
2x2w 2ohm FUSE RES
Any help would be greatly appreciated!
Posted on May 28, 2018 at 7:25 PM
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