StagePass 300 Yamaha

I've only ever seen blown channels. Beware antiphase outputs . Increase the fan apertures while in there. Schematic as .rar probably on eservice.com , opens to Yamaha-Stagepas300 pwrmix.part1 then pdf I would drill open some of those tiny vent holes and open up the outlet side of the "main " fan and see how it fares after that

It's not a heat issue, these units can fail on switch on or after any indeterminate period of time, sometimes they don't fail at all for weeks then fail several times in one gig.

Yamaha are quite aware that there is a problem yet don't seem to want to share.

Blown channels are often caused by using metal bodied right angle jacks in the mixer unit. If two plug bodies touch, or one touches the metal handle it shorts out one of the amps.

Ron

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You would think Y would put some clear plastic sleeving over that nearby handle, but I suppose its absence is a money earner Someone phoned up 2 weeks ago for me to repair one where he had done that with extension speakers, a snare drum brush bridging the 2 metal barrels of the speaker lead plugs. Who in they're right mind would think that one connector barrel was at earth and the other is hot ? Hopefully he's chucked it now . Do you know of a forum/thread discussing that "protection" drop-out issue

Yamaha was about the first to adopt PbF , 2001 IIRC, so all Stagepas will likely be PbF

Is it always preceded by a pop , ala

epas-300-problems.html

Then genuine or false protection issue ? pops due to protection cutting in or preceeding the protection ? Ignoring the internal to ps protection . Both the outputs are monitored for protection and only the +rail , presumably an advantage of antiphase operation. If no PbF issues and no blown amps then I suppose a stopgap measure would be to downgrade the output end pick-offs by a half or so, until a fully known cause is found

Assuming you have a working amp , is there an o/p pop if you trigger the 802 opto into protect mode?

I do own a StagePas myself, which has so far not exhibited the failure. I`m not going to go poking around in it just for the sake of it.

I hear of faulty StagePas units all the time, I direct them to a local Yamaha repair agent, but it would be nice to know what causes the units to fail

802

Especially with PbF inside, if it ain't broke, don't poke.

This is one of my repair briefs that may well be consistent with your query symptoms, causation would seem to be PbF or electrolytic intermittent punch through

intermittent then no left channel (no pan control on this amp so L-R a bit specious), 150W per channel in the blurb. Speakers measure 5.6 ohm so probably 8 ohm. Not possible to play around with it without disassembling as, all wrapped inside one another. Marked all the bits of celluloid and sub-assemblies before disassembling. No obvious solder problems or wobbly bits under illuminated mag glass. The power board with 2 fans is confusing because what looks like 2 channel power amp farthest from the mains inlet filter chokes is a very distributed SMPS, split into 2, especially with a thermistor on a vaned heatsink with a

7 pin TO220 device either side, that look like TDA... monolithic audio o/p blocks. But those devices are TOP249YN smps drivers. The compact lump nearest the mains inlet, that looks like a compact SMPS, contains 4 TO220 devices , ST P14NF12FP 120V 14A mosfets. Generally i would say this was well constructed except for the conical greyish silver solder points. Perhaps 1Kg of the overall 2.5Kg is the weight of the thick steel top fascia plate and the robust black enclosure box of composite/plastic/rubber or whatever thick and dense formulation. One potential problem, is all the pots are pcb mount only with no bush nuts to that nice steel fascia, i've checked the dual master one with DVM but seems ok. I don't know what the electrical/electronic term is but in nuclear power - the "void coefficient " could be a problem. 2 fans , 1 1.5 inch and the other 2 inch . If either of those stopped with all that power consumption in a small space , I wonder what the result would be. Hopefully the thermistor would initiate a shut-down procedure. Because of the coil blocking removal of the bolt through each pa heatsink. To remove the mosfets desolder the nut side one, slackening off the bolt enough to de-solder the heatsink and then remove the other mosfet. My replacement were not insulated so the mounting hole through the heatsink needed enlarging to take a full depth insulating bush as well as mica. Class D, but not unipolar design, and 2 "channels" of SMPS for + &- 2 neatly shorted D-S-G mosfets and 2 neatly o/c 0.056 ohm wide SM resistors leading to each of the o/p filter electrolytics, no overheating, charring or burning anywhere. So assuming no leads to speaker or speaker problems what would cause this ? I had previously desoldered one of the o/p electrolytics on the other more accessible board to try and read the ident of the obscured mosfets and that cap presumably only had marginal soldered contact via junk lead-free solder, could that be a cause? the 2 off per channel 50V, 470uF HF filter caps across the output. Here is a pic I took of what was probably tin pest. Ignore the top pic as just a control showing normal silvery appearance of pins after desoldering. The black cap, the top pin could be pulled out and the bottom one needed desoldering. It is just about possible to see the all grey dusty covering to the top pin. So that 100 percent tin layer eventually turns to the grey form , expanding in the process. So like a weed growing through concrete it forces the solder apart as well as in itself being non-condusctive. The solder joints on the caps and elsewhere otherwise looked normal, only this surface layer tinning of the pin had transformed to grey. Located down to one of the power amps, permanent out rather than intermittant now, nothing found twizzling. Both have indirect edge connector pairs . It would be nice to swap them over because the duff one is not very accessible without making a pair of extenders, but probably not advisable, as maybe not identical, the feeds are different. With maybe 250KHz on these amps in operation I'm loathe to put a scope around the mosfets and will try and diagnose cold. find space on or off both pa to replace the 50V 470uF pairs with something higher than 50V. They are part of the LC LP filter straight across the output via the o/c Rs. As there is nothing wrong with the speakers or leads then internal punch across these downstream of mosfet electrolytics (test to 60V ok) is likely reason for blowing the 0.056 ohm resistors on the outputs and then blown mosfets.

That brief was from before I had a schematic for the 300 or the 500. PA component level schematic with similar D class in the 500 manual. The 470uF cap is not on the audio o/p filter but must have been one of the main DC rails. What effect would intermittant non electrical contact of one of those , due to tinpest, have on functioning of the amp when there is plenty of capacitance at the ps ?

Well that's an actual component failure, the fault I`m on about is intermittent and very common. It doesn't seem to be dry joint or heat related, sometimes they come on then go off, sometimes they fail to produce sound even tho the meters show a signal.

Switching of and on again generally restores operation. It's become a common fault and a shame because the units are otherwise very useful for small gigs and if not for this lack of trustworthiness would be lucrative for hire purposes.

I imagine that the typical case of output device failure might be caused by the unit being thrashed beyond its design limits (as so often happens)

Ron

query

punch

I think I've repaired 3 different 300 Stagepas. Each one dealt with the blown amp and while in there, drilled open those tiny inlet holes and propped open the outlet vent. None of them have returned so may or may not be relevant. One of them the smaller fan had stopped functioning so probably contributory. One of them the owner had noticed the outlet air was hotter than usual (same set and useage as normal), Later versions had more holes in the outlet vent which suggests a heat flow problem , then after that perhaps PbF problems. I'll have a look at the thermistor/thermal protection area of the schematic some time

query

punch

I would think thermistor TH810, Q801, Q805 and PS PWM controller IC804 are just doing their job which is fine when amp is new but not when a bit of dust and grime accumulates , component variation etc.

This is my earlier observation about the outlet fan , first air is directed at a wall 3/8 inch from its blade, then forced through a very small grill

The outlet grill , on this presumably later version, is under the master control in the pic orientation. This pic shows about twice the number of slots as the one I have here, so in recent years they have punched more slots. This one is just the slots in the black area of that pic, not the continuation towards the master control. I'm not in the position to retrofit slots, but can bend and lift that corner with a standoff and elongated fixing hole. The inlet holes are a line of 1.8 mm holes , directly under the top handle in that pic, so obscured."

Mine doesn't have the slots in the lighter grey area, but the slots in the dark area are longer than those in the pic and follow the lower edge of the tapered grey screen print.

Any road up, it's not a thermal problem as it can happen on switch on.

Ron

None if the ones I've seen for repair have been used inside the speaker , excessive vibration causing your symptom from being used as powered speaker? Any amp hiss from the speakers when the amp dies? As far as I can see all the protection measures kill all power rails so no long term continuing of any level LEDs. So what is common to both ch in the preA ? As there is no stereo controls with this amp , presumably the fault is between where the inputs are commoned and where they are divided into the 2 PAs

I have seen the following problems occuring on StagePas 300 :

se they need longer cables. This won't ever work; Most industry standard ca bles having 6.3mm jacks are meant for guitars and other relevant instrument s,Conductors inside are thin and coaxial having enormous capacitance and ve ry large resistance.

You need to order your technician or build yourself a pair of REAL Loudspea ker (twin-lead and sufficient thickness for 150W power handling) cables hav ing mono 6,3mm jacks end to end. You won't burn your amp that way.

also -

I have noticed a problem w. my set that showed after 15 mins of operation t he following problem:

Sound cut off, replaced with low frequency hum (thus amplifier is still act ive), Limiter led (red on bar graph) stuck ON, Turning it off and after a f ew minutes back on solves the problem.

That problem was traced down to an 7915 voltage stabilizer on the main prea mp/psu board, having an output of -8V instead of -15 on normal operation an d after 15 minutes that voltage fell to 0 volts. Replacing the 7915 with an other fixes the problem (solid -15V on output). My Stagepas 300 has an 7915 with plastic casing (too large heat resistanse to heatsink, I guess, and a semiconductor fatigue resulted to that problem). It looks that using a met allic 7915 is possible as the heatsink is electrically isolated from the re st of the circuit on my revision, if in doubt use some mica - plastic ring isolator there.

Cheers.