Fender Passport Venue

[dugdiamond]

Hello Friends and everyone else too...
I have one of these ugly R2-D2 Public Address systems on the bench.
Stuck in protect mode.
I managed to get the actual correct and genuine Fender service documentation.
However it does not include schematics for the SMPS and/or the Integrated Power Amp board sharing the same heatsink.
They simply list the PCB Amp assy and the PCB SMPS assy together as a modular non service replacement part.
It appears Fender only supports a complete swap of SMPS and the PA boards together but no other support or explaination of the circuit topology. No schematics for what is the meat and potatoes or the life and soul of this butt ugly all in one sound reinforcement system.....
I have been up all night looking for some sort of schematic and trying to figure what does what and what is pulling down the PS causing it to go into protect mode.
I havent looked up the output device application notes yet, but are they really getting 300 watts per channel out of a pair of these IRFB4020 devices on each channel?
I assume that this is all done thru the same magic as in the way an SMPS works???
Well I might have to bite the bullet and learn some more about the wonders of Class D Audio....
( I have just barely begun to feel all warm and fuzzy in the comfort and warmth of HOLLOWSTATE. As if it was that much of a comfort zone, I am being pushed into working on this abomination! )
My all night internet cram session has given me two revelations.....
First is DAMN!!!!! That ugly R2D2 Harper Valley PTA sound reinforcement system is Freaking Expensive! No wonder why mommy and daddy have been so adamant about fixing this up for their young next American Idol kids' garage band!
Ok so here is how far actually have gotten.
The kids uncle brought this to me to look at anyways, right after I already mentioned it wasnt my thing over the phone.
First thing I noticed was that the speaker leads were taped up like they had been spliced.
Knowing how many hidden screws and what a pain the older ones were to work on I really didnt want to look at it further, but those taped up splices were too hard to ignore as a clue that this might be an obvious EZ fix. Yeah right oh ol Sherlock!
I figured probably cooked the output. So reluctantly I said I would see what I might do....
First thing I did was try to power it on and check for DC on the output but it immediately cuts out due to the protection circuit. So I started twisting the golden screwdriver and liberated the PS/amp module and right away,,,,, well right away after using my Dewalt on all those screws!
I tested the junctions of all four transistor output devices using the diode function on my DMM I took readings from EBC / CBE / BCE / ECB/ thru each device on both power amp channels. Of course in circuit testing it appears that all I was really doing is charging capacitors or the devices would have a intial rise before conducting. It is difficult to fully test in circuit but I did not notice any drastic shorts . Each device in both channels all had similar readings on the DMM diode setting and also when reading back and forth using the resistance settings and nothing noted below a few thousand ohms to ground on opposite pins from each pair .... if I do recall correctly????
Basically all my readings from both channels on all four devices are all very close to being the same as each individual device. So for now I will guess they are one of two possibilities of either all good or all bad! With no full on shorts,, t think at this point without removing each device I will guess that they are ok....
But something is likely pulling down the PS rails and making it shut down.
I will need to wire up a test harness or jig to safely test this amp with the power removed from the Power amp section and see if it goes into protect. I can also check the Voltages that the amp should be seeing.
Man! I just wish I had schematics for the SMPS and the POWER AMP or .....
do I just try and source the whole populated boards and do a swap????
Sure would make things easier.... After I make a harness, I can play around with the high voltage and see if I am getting 50v plus and minus..... Is there a way I can test these rails under simulated load and measure
The mains will be powering my test harness thru my all in one variac/auto/isolation transformer with digital volt and current meters. Its a pretty cool setup.

[Jon Snell]

The power supply will run with no load. Have you tested it?
If the power supply is dead ... but it apears not so check the output diodes if it still goes into protect mode when the amplifier is disconnected.
That will prove which way you need to go.
Mind your fingers, charged up main smoothing capacitors bite. Lots of angry pixies in them!!

[Enzo]

Well, IRFB devices don't have ECB terminals, they have SDG terminals.

The Venue is a newer Passport than I am. Yes, Fender expects the SMPS/PA unit to be swapped out as a unit. Way back when Passport was a new thing, they initially had the SMPS schematic, but after that, no longer. The power amp was a separate board. It was easy to unplug the power supply connection from the power amp. If that is possible inside this, it should be the first step.

RUnning blind, I'd look for shorted output devices, and then for shorted rectifiers in the SMPS.

[nickb]

Those IRFB4020's are MOSFET. If there is no short between any two pins they are probably OK. You should find the diode test passes between the drain and source pins. Can you disconnect the power into the amp board and test for a steady output voltage from the power supply? That at least will tell if it's the PSU or the amp board.

[J M Fahey]

IF >>FENDER<< will not repair it, why would you?
IF boards are available, replace them.
Get a deposit to cover cost and basic bench fee first,
If not, tell them to pick it as is.

[dugdiamond]

MOSFET : source, drain & gate......
Uhhhhh,,,, I knew there was something to this whole mosfet phenomena!!!
Yup, I realized right away as I was writing that I was dog paddling and back pedalling trying to show meaningful reasoning as to the methodology of my madness! I somehow knew that my ignorance of inexperience would somehow earn me a good dose of humility. Of course Enzo would be the one to call me out! But I do recall reading about how Mosfets behave or in some instances lack behaviour,,, Doh!!!!!
Ok, so is taking a dose of Humble Pie have anything to do with spinning old Peter Frampton music or is it more akin to eating those smart noisy birds for breakfast?!!
So, as I went a bit further down the rabbit hole.
I made up some leads to safely connect up the supply on the test bench outside of the mixer cabinet, and where it could be safely accessible to make further readings of the PS output.
I connected everything up except the + and the - high power rails to the amplifier board.
The result was no more protection fault being tripped..... So I measured the no load plus rail and it remained a nice steady 51.4Vdc with no waivering.
I next tested the negative rail with the resulting measurement mostly 51.3 Vdc but some wavering up and down a couple tenths of a volt. In other words it drifted between - 51.3 to -51.6 . I am unsure if that I was just more sensitive in my observation or if this was really so unstable. So I decided to test for AC using my "true RMS" reading multimeter on the AC setting and if there was any significant AC I couldnt find any fault. I even tried it on the counter function with no significant noise beyond the third decimal point of a single hertz.... about the same as what the stray leads already read in my environment. The nearfield common mode noise from the flourescent lights are a magnitude worse than this SMPS.... It is incredible that these supplies can be so smooth, unless I am reading something all wrong into this?
Anyways It seems supply checks out.
For giggles and grins I decided to plug the power back into the power amp again before I go further and start trying to extract components from that very stoutly thru hole double sided circuit board. ( I have tools for this and enough experience to actually succeed but I know enough to avoid such challenges if I need not have to.... Chipquick, flux, hollow tip iron attached to a vacuum pump is all great friends of mine! Yet another pretty cool piece of kit I have!)
So I reinstalled the 50v rails to the poweramp board and applied 117v to my autotransformer with only about 350mA showing up on the amp meter I wondered if this normal for this beast to idle this in protect mode? But I look at the front panel and WTF??? I dont believe it! No protection mode light??? I very quickly check the output for DC and its looking good. I shut everything down and double check all my connections and my pigtail harnesses going back into the mixer and everything checks out. I plug in my signal generator into one of the inputs and a set of shop speakers on the output side and the system is running ever so fine for three or four hours today. I have shut it down and started it back upbseveral times and it has not yet malfunctioned. I have yet to conduct any other tests but I intend to go through all the listed test points and take readings to see how it matches up to the service manual. I often thought it would be cool to have a paint shaker,..... for various creative purposes L.oL
Anyways I sm reluctant to button this up until I have some idea what goes on here..... Certainly J M Fahey makes the best business sense. Perhaps I shouldnt mess around and waste more time. Just error on the side of prudence and do a board swap out if I am able to source the parts from a authorized service center. No messing around wham bam thank you American idol band.

[Enzo]

- 51.3 to -51.6 . I am unsure if that I was just more sensitive in my observation or if this was really so unstable

"So unstable"? What is that, about half a percent? Sounds stable to me.

And remember, your SMPS runs at 50kHz, 100kHz or higher. Your meter on AC volts won't respond to that. Fluorescent light noise is 60Hz or 120Hz. And as to being clean, SMPS have been around a LONG time. I have been servicing them for at least 40 years that I can recall. It isn't a new technology, they design them well.

In taking it apart and reassembling it, you may have removed some errant bit causing a short.

[nickb]

The problem with just replacing units in toto is you miss an opportunity to learn. Also the price you will have to pay for new boards will be prohibitively expensive. If you have it, take the time and the next one you come across will be fixed faster. This impresses customers.

I think Fender and others have do not repair for a couple of reasons. One is that can get the whole caboodle for peanuts, but you can't. The other is, I suspect, they contracted out that bit of the design and know nothing about it.

Recent example. Mackie power speaker with blown combined PSU power amp module.Mackie quoted about $300. I did it for way, way under that. Very happy customer.

PS: Glad it's working, but.....arrrgghhh!

[Enzo]

Fender included the SMPS schematic on the earlier PAssports, but left it out of the schematic file for later versions. As a Fender warranty station, I asked about it, and they told me they expect service centers to know amp repair, but SMPS repair might be outside the skill set of many. And SMPS are also very dangerous to work on. So they wanted us to fix everything but the SMPS, which they would swap out as a unit. On the other hand, when I went ahead and repaired the SMPS, they always paid the claim.

And yes, I am pretty sure they buy the SMPS. The schematics are drawn by some Asian name.

[g1]

Fender included the SMPS schematic on the earlier PAssports, but left it out of the schematic file for later versions.
...
The schematics are drawn by some Asian name.

Shen Fa.
P-150 smps schematic attached:

[Enzo]

Here is the P250, I don't know what is in the Venue.

Passport P-250 Power Supply Schematic.pdf

[nickb]

Enzo, I get "Invalid file" on that P250 PS.

[Enzo]

Huh, so do I.

Passport P-250 Power Supply Schematic.pdf

[Enzo]

Well I don't know what I am doing wrong.

[Dave H]

Well I don't know what I am doing wrong.

Is this it?