CurtPalme.com Home Theater Forum

RayN999

Picked up a (fairly) cheap Marantz SR7002 off fleabay a couple weeks ago, had dented in rear panel & no power. I straightened the back panel, looked over the speaker output board & things looked just fine. A few bent speaker terminals, but nothing I wasn't able to bend back into shape. Also located service manual for it too, so all is good (so I think).

Started to troubleshoot the 'no power' issue & found open winding in the 120v/12v standby transformer. Open winding was on the 120v side, replaced it temporarily with what I had handy, 120v primary to 12.6v secondary CT with center tap not used. According to schematic, the transformer only feeds into a LM7805 regulator & a precision 5v chip providing feedback to the regulator to ensure 5v is constant for the rest of board. Board also feeds to the main power transformer & then to the rest of the circuitry.

After all of this, plug power in for smoke test, no smoke released, so I get good feeling. Standby light comes on & relay click is heard when power button is pushed. Display illuminates, but as soon as secondary relays release (I assume speaker protection relays), the set goes dark. Pull plug for 15-20 min, reapply power, standby light comes on & 7-8 seconds later, set goes dead.

I'm thinking that it might be something in the rectifier section (where the B+ & other voltages are supplied to the power amp circuitry & such), but since the regulator chips are bolted to same heatsink as the main power transistors, I haven't looked at extracting just that module on its own just yet.

Reviewing the schematic, it appears that there's a 'power good' signal that's a return to the secondary power board that triggers a transistor & releases the relay. My assumption is that this signal isn't getting asserted & the set shuts down at that point.

Anyone with familiarity with this series?

Or maybe it's time to pull out the 'scope & start probing signals....

Appreciate any ideas or suggestions.

Ray

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Does the standby LED flash after shutdown?

Have you tried monitoring the +5v standby during power up and shutdown?

Any error message on display just before shutdown?

RayN999 · Posted: Mon Jan 02, 2012 5:49 pm Post subject:

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Why are you loosing your standby voltage after shutdown? I'm not seeing where that should happen. Where are you monitoring it at?

RayN999 · Posted: Mon Jan 02, 2012 6:40 pm Post subject:

Was mistaken with that, the 5v on the standby line is just fine and stable like it should be. I was pulling this straight from where the standby board connects to the power/speaker output board. However, more digging, the 15v and 5v lines coming back from the regulator board are reading 0, so I think I got my clue. Looks like pulling regulator board and looking over the power board more for further investigation is where I have to go.

Thanks

Ray

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

You have this thing fixed yet? Should only take a half an hour to find the problem, LOL. Laughing

RayN999 · Posted: Wed Jan 04, 2012 7:49 pm Post subject:

I had a couple other projects take priority, so I didn't get back to this. I may pull the boards today or tomorrow & look them over. Not in a big rush, got plenty of other distractions here to work on also.

Thanks for your help so far...

RayN999 · Posted: Mon Jan 09, 2012 11:16 pm Post subject:

Replaced 15v regulator that tested bad, tested 5v & it was fine, so put that back in. Reassembled, plugged in, get flashing standby light for 7 sec. then it goes dead.

Back to square -1... Or maybe I'm missing something so obvious I deserve my amateur techie privileges revoked.

Maybe it's just destined for the junk heap.

Ray

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Try disconnecting CN95 from the reg board and see if it will power up.

If not then try pressing and holding the "Pure Direct, 7.1 channel Input and clearv" buttons until in power up......at least 5 to 10 seconds. If still nothing post back.

RayN999 · Posted: Mon Jan 09, 2012 11:59 pm Post subject:

Tried the 'vulcan nerve pinch' (felt like my fingers were distorted enough to press all 3 of these buttons at once), will pull CN95 & see how that goes...

RayN999 · Posted: Tue Jan 10, 2012 12:15 am Post subject:

Pulling CN95 still results in standby power loss (and the standby light quit blinking now) after 7-15 seconds or so. Guess that means there's something wrong yet in standby power, but I've gone over that multiple times already.

Since standby won't stay on long enough, I can't both put power socket in & hold the buttons long enough for that to work....

Ray

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Plug CN95 back on.

have you tested voltages including power on at standby board CN70 as per the manual?

RayN999 · Posted: Tue Jan 10, 2012 1:12 am Post subject:

Yes, that's where I started & discovered the open winding in the 120v primary. I used a 120v pri to 12v sec transformer, instead of trying to source the dual secondary transformer that was OEM. The 25v winding fed to spots on the standby board that were unpopulated & therefore completely unused. Running on its own, out of the chassis, I get the proper 5v signals at the connector to the power board. I'll have to dive back into it tomorrow & see if maybe I overlooked something on the power board. CN70 doesn't see 12v because that's 8002 version only, this is a 7002. There aren't any bridge diodes or regulator chips on the standby board, hence my choice to supply with only 12v.

Appreciate your pointers....

RayN999 · Posted: Tue Jan 10, 2012 1:16 am Post subject:

At least with my Marantz SR8000 repairs before this one, there were burned components & smoke & sparks that led me to the trouble. This one is a bit more difficult.

I got too confident & bit off more than I can chew I fear. I wouldn't try too hard at this, but I'd like to put the SR7002 in place of the SR14EX in the living room & sell off that 'boat anchor'.

Ray

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

I'm more curios if your getting the +5v return at cn70 pin 6 on that standby board. You need that to close relay RY701 to send power to the main transformer that powers the rest of the receiver.

RayN999 · Posted: Tue Jan 10, 2012 1:29 am Post subject:

Thanks, I'll put my meter on that & watch during the power cycle tomorrow. I really should get a set of micro clip leads for troubleshooting like this.

RayN999 · Posted: Tue Jan 10, 2012 3:05 am Post subject:

Since the display & other LEDs lit up when I hit power (before the 7 sec or so to shutdown), I had assumed that the primary transformer was ok, but maybe that's not even getting lit up & is just being fed from the 5v from the standby supply. I hadn't even considered that.

Guess this beast is being difficult.

Ray

RayN999 · Posted: Tue Jan 10, 2012 7:17 pm Post subject:

It's up & running!! All I did was relocate the 12v standby transformer to another slightly larger space, and it fired up (space inside the chassis is quite cramped). It's been on for 10 min. or so now. The original transformer was PCB mounted, and without going back to Marantz & ordering an OEM transformer, there wasn't a way I could duplicate the pinout & spacing, so I improvised.

I'll test it on the bench for most of the day, but things are looking good now.

(edit) Issue seems to be pinpointed. I had the RS-232 comms board disconnected on back panel while doing these tests today. Reinstalled that board (simple 4 wires connected), and the receiver standby issue happens again. Disconnect board, and receiver fires right up.

Since I have no real need for the serial comms, I'll just leave the board disconnected.

Ray

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

That's good to hear. The only thing that appears to be on that board is the driver ic. Test between pins 15 and 16 for short with you DMM.

RayN999 · Posted: Tue Jan 10, 2012 8:24 pm Post subject:

Not shorted, reading about 39 ohms resistance, varies because there's a filter cap across those two. No short between pins 3 & 4 of CN90 either.

I can just leave it unplugged/uninstalled.