Fender PA problem. Passpoprt 250

[Tilman]

I installed a new control IC today.

Before I did that, I checked the resistance pin7-5.
The instruments shows a diode between these two pins.
The old IC was dead - this is clear now.

When I started the SMPS with no load the fan did run for 0,5 seconds an than my 16A bench main fuse did blow.
I took out the IC and now "only" the 10A fuse blows.
The IC measures OK.

I guess now the switching MOSFETs are dead. I will give up at this point since I do not know the reason for this. Even if I would replace them now - they might die again...and again...

Enzo, thanks for your help!

Tilman

[David Hawn]

voltage output of Fender Passport DC/DC converter

I'm trying to figure out the voltage output of the Passport DC/DC converter. I don't own one and was trying to figure out how difficult it would be to make one. There are 4 wires, one red, one blue, and two black. The 2 black wires are probably both ground. From looking at the power supply diagram posted on this thread, it looks like the 120VAC is turned into a +/-15VDC. The "External Input Voltage" on the right side of the diagram shows two connectors, one with +/-36VDC and one with +/-51VDC. It makes sense that the DC/DC converter voltage would need to be higher than +/-15V so the 7915/7815 can regulate down to 15 volts, but 36V and 51V both seem quite high and inefficient.

Does anyone have a DC/DC converter and could measure the output voltage?

Thanks!
David

[Enzo]

High and inefficient? Well that would be if all they had to do was power the preamp. But those power amps will be pretty well starved if you try to run them on +/-18v.

The power supply makes not only +/-15VDC for the preamp, it also makes +/-51VDC OUTPUT for the power amp.

If you are running on external power from batteries, the INPUT voltage is +/-36VDC. The power amps run on that as well as the preamp regulators. The thing doesn;t pretend to produce full power on batteries. The two connectors are shown in parallel, though they are not near each other. Only the 36v inputs are labeled external input voltage.


My service documentation for the Passport series does not include the DC pack, but if you contact Fender and ask, they might have it to send you. Then again they may purchase the battery units from outside suppliers.

[David Hawn]

Thank you

Enzo, thank you for your response! I didn't realize the +/-51V was also an output, but it makes sense now.

Thanks again!

[bazb_uk]

Fender Problems

Hi, All,

I am currently working on a Fender SMPS... SO Thanks so much for the Curcuit Diagram..

Our unit kept going into protection after 5 secs of been on.

I found 2 pre amps blown on the mixer so guessed high voltage had been plugged into an input.

Although the PSU generated both +/- 50V and +/- 15V When a load was connected it was dropping to about 3v +/-

When inspecting the board I could see both the + & - 15 V regs were charged, and the output resistors. one mesured 150 Ohm, the other 210 (both labled 150) So i have replaced both Regs, and resistors and smoothing caps...

Now I get my correct voltages, But as soon as i load the - channel the voltage dropps to 3 volts. The voltage is there, but there is no power present on this channel only.

Would this point at the SM - Transistors on the Primary side of the transformer? Or could it be a problem with the output voltage sense / drive???

Any food for thought would be awesome!

[Enzo]

The power from the SMPS connects to the center of the power amp board. Disconnect that and see if the thing powers up the rest of the system. In fact, the SMPS ought to be able to power up and run all by itself on the bench. When faced with a shorted amplifier channel; for example, it will shut itself down. So when I face a Passport with SMPS problems, the first thing I check is for shorted output transistors on the power amp.

[bazb_uk]

Problems

Good day, and thanks for the super quick reply.

I have already tested the power amp, running from another +/- 50Volt supply.

The Amp works fine. My problem is defo in the Switch mode Supply.

Unloaded the power supply presents all voltages correctly. But as soon as I load the PSU the voltages drop. I've used a chain of 12volt 1W lamps (So thats not much load)

Thats less than 100mA draw on the SMPS.. The + channel works fine, but the - channel drops and flops.

I've removed both the 15v regs, (7915 & 7815) 180 omh resistors, output smoothing caps, and tryed the load test again, and still the - channel has no power output....

Next im going to put it on a scope and check the input / output waveforms of the SM transformer???

All i have left on the board is the large triodal output choke, the 4 Diodes D7, D8 , D12, D13 and every thing before. What component could still allow full voltage output +/- 50 volts. But mean that the negative channel has no power output (less than 100mA?)

[Enzo]

Well, you know the waveforms will just look like hash. SImple enough to check if one of those windings is open.

DId your 15v rails work before you removed them? They draw off that same supply. If 100ma collapses the -51, why would it not also if the -15 drew that current from it?

Unless we are looking at different prints, D7,8 just run the fan.


STray coupling could be rectified to provide voltage at no current. Look for cracked solder around the smooting inductor and transformer secondary.

[bazb_uk]

D10 and D11 rather than 7 & 8, Sorry. Need more coffee!

You are right, the -15 also collaped the voltage, Thats why I have removed all the +/-15 volt supply system. As its just bunged on the +/-50volt output.. I thought one of those might be drawing the current, but now all the 15volt components are removed.

This lack of current is still present. I think the Winding are good & can see no signs of track damage, I guess my next stage is to mesure the voltage Open curcuit and under load from before the rectifyer diodes, and the voltage drive to the SM transformer to see if its been driven well enough.

If the voltage drops before the SM transformer then im guessing its one or 2 of the IFR840's up the duff??

Or could it be the controller, failing to throttel up the drive as the output is loaded?

Does the unit monitor voltage on both channels or just 1?

[bazb_uk]

Psu working! Now what?!?!

Enzo! Thanks for your help so far.. You clearly are a electrical legend wizard!


I've got the switch mode PSU working!!! Replaced both + - 15volt reg, Current limit resistors, and output smoothing Caps!! Now I get +/- 50Volts and +/- 15volts.

Succsess in loading the 15 rails with 1Amp burst. (Max of the Regs) and 500mA constant... ALL OK...

I can plug the PSU into the Power Amp board, and apply my own input and the speakers work fine 100%

But when i plug in the front panel / mixer board, (covered in TL072CP OP-AMPS) It all flops out again...

There doesnt seem to be much to this board.... 17 x Op-amps, 31 x V-R's, 31ish x Eletro Caps 5 x transistors.... and many resistors.



I cant think that any component other than the Op-Amps could be causing the +/-15 to drop off to 3 or 4 volts, and over load the PSU..

Any1 come across this before, and knows the solutions?

[Enzo]

PLEASE BE CAREFUL. I am getting the impression you do not know how SMPSs work. They are extremely dangerous, the mains is DIRECTLY rectified and filtered. You have the deadly combination of HIGH DC voltage and all the current in the world. All the primary side electronics are NOT REFERENCED TO GROUND. You cannot just clip your scope to it. Your primary side must be working, or you'd have no secondary voltages at all. You have V+ even when V- collapses, so forget the IRFP840s.

The switcher works are very high freqs, and it is not sine waves. The hashy junky waveform will have a hard time making sense to your meter, which probably doesn't respond well at 50,000Hz and up.

Your V- was bad before, even with the -15 stuff gone. SO what did you find that restored it?

If the mixer panel still loads down the +/-15, then start looking. Any of the ICs get warm or hot? You have op amps on the main mix board and on the mic board, plus pairs of clamping diodes on the inputs

[bazb_uk]

Please dont worry about my electrical safety, I've designed and built SMPSU's and PowerAmps, aswell as TV PSU's .. Everyone else beware thought!!! Danger of Death .. But this Fender is a bit topsy tervery, and i dont have much time. Hoped someone else might have the answers....

SMPSU is now 100% working... I've load tested it for an hour and its like new.. The -50V smoothing Cap was completely FUBAR along with -15V Current limiting resistor (White 5W jobby)..and both 15 regs were blown



Problem now, Seems to be somewhere on the mixer board... Good idea about feeling the IC's for heat, but I susspect this will result in PS damage to the 7815 and 7915 again. Think im going to remove the IC's 1 by 1 and test them on proto board

[Enzo]

Your 7815/7915s should have thermal limiting within themselves, and we won;t be leaving them on extended periods while loaded down.. If you are concerned for them, then power the mixer panel up from a bench supply.

Check those clamping diodes at each input on the mic preamp board. Two shorted will tie the 15v rails together, and voila. And just to divide and conquer, can you disconnect the mic pre board from the main board?

In general, in systems with a lot of parts, it will be the IC that interfacces to the real world a LOT more often than one in the middle of the circuit. That points us towards those ICs on the mic board.

Pulling all the ICs off the board sounds like a lot of excess effort to me.

[bazb_uk]

next prob

Enzo, Hope your well?!

I have got new 072’s now, and replaced all, tested the ones coming out and 5 were blown and shorting out internally.
I now have another problem. The Mixer seems to work OK,
Now im back to the PSU.. The +/- 15Volts simply overheat and shut down after a min or so...

The input voltage to this (the +/-50volts) is reading 66volts before the limit resistor and 44~volts after... According to the 78 & 7915’s datasheets 35Volts is the maximum input voltage..

So im guessing the +/-50 rails are way over voltage. And the huge voltage drop in the regs is causing them to overheat and shut down loaded or unloaded.

Any ideas what could cause the +/-50 volts to be over voltage so much? I know there is a monitor out / drive in throttle system, but don’t see how this could become damaged and cause this fault. Any ideas here?

[Enzo]

Are you in the UK as your name suggests? Any chance the SMPS is set for 120VAC operation?

And are ALL the loads on the SMPS when you take these readings?