Tech Info Question -- Panasonic SA-PM19

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RandomInspiration
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Tech Info Question -- Panasonic SA-PM19

Hello Folks!

I found my way here in the quest for tech info on a bookshelf system made by Panasonic: The SA-PM19 Smile

First, the bad news: After a few years' service, one of the onboard controllers gave up the ghost.  So, after salvaging my CDs from the unit, I decided that it'd make a nifty small amplifier project!  I'm hoping to take the 140 Watts of great sound with me for presentations with my laptop; and I believe that I've now got it mostly figured out.

Mercifully, the digital rubbish was designed to be componentially separated from the amplifier board, and the interfacing has been fairly easy to figure out: I now have power going into the amp, the cooling fan worked out, left and right channels ready for input.  However, the volume control for this unit is handled through the now-defunct controller system; and the levels seem to be run into the amp board via the DCDET pin on one of its headers.

Since the uC system turned up its toes before I could measure any levels at all, I am at a loss as to what supply to reference this pin to for volume control.  I don't see why a simple pot voltage divider wouldn't work; but, again, I don't know what levels we're looking at here.

So, does anyone have specs for this particular animal which they'd like to share?

Thanks again, and have a great day!

dans_repair_service
dans_repair_service's picture
In order for me to provide

In order for me to provide you with the best info, I need to know what happened to the unit. What do you mean when you say that one of the controllers gave up the ghost? These units have a known problem where the CD mechanism jams up. There was an engineering ECO to address this. If you can provide me with a few more details on the condition of the unit, I will look up the prints and try to answer your request.

Dan

RandomInspiration
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Hello Dan!

Hello Dan!

Thanks for dropping by and lending a hand Smile

Here's the scoop on the uC side of things:

Starting a few weeks after the unit was put into service (5 years ago), the CD player started to exhibit signs of a degraded laser: Hypersensitivity to scratches and dust.  Couldn't take it back to the store for an exchange/refund; so I just wrote the problem off to rogue ESD damage; and just "got on with life."

A couple of months ago, the remote seemed to have suddenly gone away.  Changed the batteries: No luck.  Wrote this one off to tin whiskers or something else.  Again, just "got on with life."

A week ago, high-frequency clipping/digital noise started creeping through the speakers after a couple of minutes of play at low/modest volume.  Heat was not a factor.  My gut told me that something was going on here: We now had multiple disparate functional failures in a single unit.  Coincidence?  Hmmmm...

A few days ago: Complete lockup.  Soft-powerup failure; nothing but the red pilot light would work.  Allowed the system to set for several hours off the grid to crudely rule out latchup: No dice.  In the end analysis, the boat anchor even swiped my CDs!

A quick post-mortem look about the web found similar failures in others' experiences.  Most seemed resistant to commonsense repairs (replacing the remote, redoing the CD changer module, etc.).  The one thing all of these failures had in common is the uC setup which runs the whole mess...

In any event, I wrangled my poor captive disks from the corpse (I truly did try the civilized approach first); and put them away.  My further autopsy found a perfectly good and strong amp and power supply beating as the heart of the unit; so I decided to do a little bit of salvage projectwork and make the world's most powerful laptop amplifier.

Which brings me here today!

While waiting for a kind soul to reply, I did manage to feed a micro mp3 player's output into the right and left input channels on the amp board's header just to see if we'd get any squeaks from the patient.  Indeed, full throttle output!  Clean and clear.  Still wondering about the DCDET pin; but it doesn't seem to matter to this aspect of the project, as the amp's output is directly controlled by line in.  Simple Cool

So, I guess that what I really could use at this juncture is specs/advice concerning proper line level for the L_IN and R_IN header pins with respect to SGND; as I don't want to blow the unit with too much amplitude at the input.  I'd also like to do a little ESD-proofing for these pins with a couple of 10K resistors as well: Thoughts or ideas?

Finally, according to my trusty old meter, DC coupling throught these inputs doesn't look like an issue here.

Thanks ever so much, Dan!

dans_repair_service
dans_repair_service's picture
This may take a while, but I

This may take a while, but I think I have the schematics for this unit somewhere. I will try to pull together the info you need and post it here. If I understand things correctly, you'd like to be able to control the volume using the control in the unit, right?

Dan

RandomInspiration
RandomInspiration's picture
Awesome!  And thanks again,

Awesome!  And thanks again, Dan.

As far as a formal volume control goes, well, it looks as though a simple dual-gang through the existing cabinet hole will work in place of the encoder which came stock.  Indeed, without some serious homebrew work with the original scheme I don't think using the existing encoder system would be a good play; as, again, everything goes through the suspect chip network.  Pretty much all trashbin items...

Indeed, I was delighted to see that I could simply control the volume straightaway via the input level -- so there's really not too much needed here apart from basic specs/advice concerning proper line level for the L_IN and R_IN header pins with respect to SGND; as I don't want to blow the unit with too much amplitude at the input Wink

Anyway, have a great day; and thank you for your kind assistance!

kelby sagvold
kelby sagvold's picture
Hi i was wanting some help

Hi i was wanting some help with my sa-pm19

kelby sagvold
kelby sagvold's picture
hi im looking for help with

hi im looking for help with my sa-pm19

RandomInspiration
RandomInspiration's picture
@kelby sagvold:

@kelby sagvold:

If you need help related to this thread, please feel free to let everyone know what the exact issue is.

Have a good day --

lwnielson
lwnielson's picture
I just bought a used SA-PM19
I just bought a used SA-PM19 off Ebay and found that the CD changer isn't working;  Tray #1 is stuck inside.  With my older Panasonic, very simiar model, the CD trays used to fan out  to check the CDs, so I tried that with this one and now Tray # 2 is stuck open.  Is there a not-too-complicated way to open the CD unit to free the two trays, or can I even replace the entire CD module if one is available?
 

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