RX-V3000 burns resistors as soon as it's plugged in

Have you checked carefully for cracked solder joints on the sub power board? I just repaired a CD player were the rectifier bridge "legs" were all loose, it would work sometimes and sometimes not. Resoldered it and the pass transistor next to it, and it works fine. I would re-solder them just to be sure, also the legs of the transformer if it's board mounted. I've found those joints cracked too.

Have you replaced C311, 10uF 25V I think? Remember, this whole circuit is energized any time the unit has mains power and a couple decades is a long time for a cap to be exposed to ripple current.
 
Revisiting the sub power board.
Replace C311, 312, 313, 314 if not already done.

Pull CB507, what is +MB at W311?
You had +21Vdc in post #44 so possibly problem is intermittent.
If possible measure Vdc one side of R313, repeat for other side R313 (measure to GND)
 
HPMguy said:
Have you checked carefully for cracked solder joints on the sub power board? I just repaired a CD player were the rectifier bridge "legs" were all loose, it would work sometimes and sometimes not. Resoldered it and the pass transistor next to it, and it works fine. I would re-solder them just to be sure, also the legs of the transformer if it's board mounted. I've found those joints cracked too.

Have you replaced C311, 10uF 25V I think? Remember, this whole circuit is energized any time the unit has mains power and a couple decades is a long time for a cap to be exposed to ripple current.
Click to expand...
the sub power board was my first task...I replaced every capacitor on that board, replaced the relay, replaced the diode, the rectifier diode, replaced both transistors. Now I get 21.4 vdc from the rectifier diode when the power board is disconnecrted...it drops to 9 when I plug it into the function board. I will re-check all my solder joints. Thanks.
 
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mbz said:
Revisiting the sub power board.
Replace C311, 312, 313, 314 if not already done.

Pull CB507, what is +MB at W311?
You had +21Vdc in post #44 so possibly problem is intermittent.
If possible measure Vdc one side of R313, repeat for other side R313 (measure to GND)
Click to expand...
There are but three caps on this U, C model power board...C311, 318, 315...318 is a safety cap. All 3 have been replaced with the proper capacitors. Q311 and Q315 have also been replaced. The relay has been replaced. The rectifier diode D314 has been replaced.

W311 on the sub power board shows 21.4 volts until it is connected to the function board CB507. Voltage at W311 on the sub power board - and CB507 MB+ then drops to 8.9 vdc.
 
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Dire McCain said:
There are but three caps on this U, C model power board...C311, 318, 315...318 is a safety cap. All 3 have been replaced with the proper capacitors. Q311 and Q315 have also been replaced. The relay has been replaced. The rectifier diode D314 has been replaced.

W311 on the sub power board shows 21.4 volts until it is connected to the function board CB507. Voltage at W311 on the sub power board - and CB507 MB+ then drops to 8.9 vdc.
Click to expand...
I have not read the entire thread and am not intending to, but if connecting this connector is draining excessive current, you need to divide the circuits it feeds into segments, and physically disconnect those segments at first. Then upon reconnecting each segment one by one, determine which one causes the ‘short’ and narrow down the zone until you find the culprit part, trace, or solder joint, etc.. I think you’ll be surprised at the potentially silly cause you’ll find. Good luck.
 
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Sparkplug said:
I have not read the entire thread and am not intending to, but if connecting this connector is draining excessive current, you need to divide the circuits it feeds into segments, and physically disconnect those segments at first. Then upon reconnecting each segment one by one, determine which one causes the ‘short’ and narrow down the zone until you find the culprit part, trace, or solder joint, etc.. I think you’ll be surprised at the potentially silly cause you’ll find. Good luck.
Click to expand...
Yes, I have done that. Disconnected everything related to this connector on the board. Then replaced them one at a time. Voltage remains low at CB507 but goes lower and become jumpy when CB509, 510, 511 and 517 are reconnected.
 
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Dire McCain said:
Yes, I have done that. Disconnected everything related to this connector on the board. Then replaced them one at a time. Voltage remains low at CB507 but goes lower and become jumpy when CB509, 510, 511 and 517 are reconnected.
Click to expand...
The connector itself, I’d cut off or remove all wires to it and see if it causes the same fault upon insertion …
 
What sparkplug means is that there are different voltages going through the connector to function CB507, three to be exact.PRY,+MB and MB. So identify which wire is which and remove one at a time from the connector and plug in the remaining 2 at first , check the 21.4 volts . if its good you know that the wire you have disconnected feeds something that is bringing the voltage down. If not then return that wire and remove another one and check for the 21.4 volts again. do this for all three wires. Also if there are other connectors that feed off the function board CB507 disconnect them before you do this test. if the 21.4 volts is there after individuals testing all wires then its one of the other boards the other connectors feed. relate the process again doing one connector at a time with the others removed.

Long process but you may get lucky and its on the Function board.

I had to do this on a Carver amp and it was a couple shorted caps on a 10 volt rail took me hours to check each cap on that 10 volt rail . had to be at least 20 of them. And to test I had to remove each one to be sure.

Athanasios
 
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Nashou66 said:
there are different voltages going through the connector to function CB507, three to be exact.PRY,+MB and MB. So identify which wire is which
Click to expand...
The three wires are +MB(supply), MG(GND) and PRY(return wire for protection relay activation from mcu, it will have 0Vdc since order not given)

OP has disconnected all connectors from the function board and pulled IC528 (5V regulator), +MB still goes low, C697 replaced.
Problem appears to be in the area of Q506,7. The ^MB link above C697 appears to go nowhere.

Currently two trains of thought, i)current drain in the area of Q506,7 ii)the psu is failing under load

For i) differences between schematic and board identified, pix requested.
ii)consider "testing" the psu by pulling CB507 and insert a resistor (1k/1W) between the females of the +MB and MG, measure voltage at +MG.
This should draw about 20mA, if ok then try 100-220ohms, ie upto 200mA. thoughts?
 
I've been looking at the schematic for this thing for a while, waiting for it to cool off enough to do some watering in the garden, and found another few things I'd personally check out.

There are three 1000uF 6.3V (C660, C661, and C664)caps on the +5M1 and +5M2 lines adjacent to the reset function, and these will be powered on any time the unit is plugged into a live outlet. My experience with caps in those positions is that they are very often bad. I'm reaching my limits of electronics knowledge here, but it is possible a bad cap (electrically leaking to ground) could pull excess current through the regulator to leave the two 5V lines (4.9 and 4.8V on the schematic) at full voltage but pull down the 12V line (+mB) to 9V? There is also a 0.047? uF 5.5V (C663) cap in that circuit, and C633 is a 0.47uF electrolytic. Those very low uF value caps are almost always dead, at least having high leakage and should be replaced with film caps.

I'm still looking for where else +MB goes, I suspect it will be marked only with a pin connection at a connector or another arrow on the board in some remote place -- I really dislike this schematic, and I don't have a layout in the pdf copy I have so I can't even trace down board positions.
 
Pulling IC528 "should" rule out the +M1, +M2 rails/C660,1,2 however since there is a mismatch with the schematic it's probably a good idea to replace "all" electrolytics in the area.

I'm not sure what C633 and Q507 do, seems wrong, maybe sparkplug? Replace C633 as suggested above
 
Q507 is probably a latch circuit to hold the amp in the off state on a protection fault, requiring power off to reset. If C633 is leaking it might have the reset latched on and +MB pulled down. Q507 shorted might do the same thing.
 
mbz said:
Pulling IC528 "should" rule out the +M1, +M2 rails/C660,1,2 however since there is a mismatch with the schematic it's probably a good idea to replace "all" electrolytics in the area.

I'm not sure what C633 and Q507 do, seems wrong, maybe sparkplug? Replace C633 as suggested above
Click to expand...
C633 (47uF 16V) is a high frequency bypass filter on IC524 +Vcc and +Vdd lines to ground. (based on my schematic). Checking its condition or perhaps changing it (and similar ones, there are many) is good advice.

Q507 and Q506 form a differential pair whose outputs (collector voltages) are sensitive only to the input voltage difference between the base voltages of the two transistors. I have not looked into what they’re driving here. Probably providing a constant current source for whatever comes next.

Also, under the right conditions, the output (collector) currents are independent of the input (base) voltages. R543 is probably added to extend the linearity of the differential pair.

Edit: The above explanation refers to the DSP schematic of RX-V3000, not the function schematic portion which is the focus here. Yamaha seems to have used the same designator numbers for transistors, resistors, etc. from section to section, a very confusing practice if you look at the schematic for the first time.
 
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Reads like I'm looking at the wrong schematic, C633 0.47uf/50V?
This is what I'm looking at,
 

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This post was deleted due to schematic mix up. Please continue on to the post below.
 
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Okay got it … I was looking at the DSP schematic while you guys were on function schematic, they both have C633 and Q507. Designators are reused from section to section.

At any rate, I generally agree with HPMguy, Q507 seems to be a latching mechanism of sorts … I’ll have to look at it some more …
 
Back to regular programming …

Question: In the following,

BE915104-F50F-49FA-A599-76FFB999CD77.jpeg
+MB is feeding a 5.6V voltage regulator (NJM78M05F A), is that voltage regulator healthy? Is there still excessive current draw if its input is temporarily disconnected? Apologies if you have indicated this in previous pages.
 
Sparkplug said:
+MB is feeding a 5.6V voltage regulator (NJM78M05F A), is that voltage regulator healthy?
Click to expand...
+MB should be about 12Vdc however it's reading low (5-7V???) probably due to excessive current draw.
OP removed the NJM (IC528) and +MB was still reading low. This is a critical point so happy if OP would again confirm.

The ^+MB above C697 is not referenced on the function board schematic, maybe an omission
 
mbz said:
+MB should be about 12Vdc however it's reading low (5-7V???) probably due to excessive current draw.
OP removed the NJM (IC528) and +MB was still reading low. This is a critical point so happy if OP would again confirm.

The ^+MB above C697 is not referenced on the function board schematic, maybe an omission
Click to expand...
Here’s some deja vu for you @mbz , in the following section, maybe the OP could connect the three pin cable but disconnect the indicated connections in red. If +MB drops, the connector itself or prior circuits (supply, etc.) would be suspect. If all good, the removed connections can be restored, one at a time, to see which one prompts the excessive current draw thus eliminating other sections. After that, other steps may be taken. If he hasn’t done all this already that is.

F5A03C23-5716-4A83-A3FB-49FFC1E1C9A0.jpeg
 
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