I recently acquired a non-working Fender Passport PA system. The prior owner believed that the issue might have been related to the transistors it uses (which is covered here in another thread) but my unit seems to check out fine.
The power amp/mixer utilizes a switching power supply (SMPS) which seems ot be the source of the problem. This youtube video shows the voltage (51VDC per side) which should feed the amp but mine doesn't show anything.
REPAIR FENDER PASSPORT 250 in Protect mode - YouTube
I'm not an EE and don't really know where to start troubleshooting the PSU for likely components that might fail. (Yes, I know there's high voltage involved and will short out the capacitors ).
The service manual is here:
FENDER PASSPORT PD-250 SERVICE MANUAL Pdf Download | ManualsLib
I don't believe there is another power supply out there that I can easy swap in so I'm left with working on this thing 🙁
If anyone has any recommendations on where to look or even what parts can be tested "in place" without having to first unsolder leads?
Thanks in advance.
Some pictures:
I don't think the unit uses blade style fuses but I'm not sure what these are for?...
The power amp/mixer utilizes a switching power supply (SMPS) which seems ot be the source of the problem. This youtube video shows the voltage (51VDC per side) which should feed the amp but mine doesn't show anything.
REPAIR FENDER PASSPORT 250 in Protect mode - YouTube
I'm not an EE and don't really know where to start troubleshooting the PSU for likely components that might fail. (Yes, I know there's high voltage involved and will short out the capacitors ).
The service manual is here:
FENDER PASSPORT PD-250 SERVICE MANUAL Pdf Download | ManualsLib
I don't believe there is another power supply out there that I can easy swap in so I'm left with working on this thing 🙁
If anyone has any recommendations on where to look or even what parts can be tested "in place" without having to first unsolder leads?
Thanks in advance.
Some pictures:
I don't think the unit uses blade style fuses but I'm not sure what these are for?...
SMPS are very dangerous. Don't probe around with the power on, and make sure the line cord is unplugged & mains caps are discharged before you touch any metal. As always, don't probe with both hands. Voltage over 25 from one hand to the other can stop your heart. No jewelry on hands, wrists, or neck. 1 v @ high current through a ring can burn your flesh to charcoal.
I've fixed 3 SMPS, an Allen organ power supply, a Peavey amp, and an HDTV converter. The Allen, the old leaky mains caps ( the 400 v rated ones) had blown a NTCR they used instead of a fuse on the 120 vac feed because it was cheaper. New mains caps & new NTCR fixed it. I also replaced all the other electrolytic caps, which were ~30 years old.
The Peavey CS800s, a leaky 47 uf cap on the 5 v control circuit had blown a 160 ma fuse. New fuse & cap fixed that. I also replaced all the electrolytic caps in that power supply since they were 26 years old. Note mains caps in SMPS are usually low ESR ones. I didn't replace any caps in the amp circuits; it still sounded good and had plenty of power.
A third SMPS I fixed was a Farnell HDTV converter. It got where it wouldn't work on cold mornings but did on warm days. 8 new electrolytic caps fixed that; I didn't change all of them. Of course the mains cap was probably the culprit, but I also replaced some of the 5 v supply & 12 v supply secondary caps. It was only 8 years old.
If the fet is blown (all pins shorted together), I've never managed to fix any SMPS like that. PC supplies. Fet takes out too many parts to be worth fixing.
Happy hunting.
I've fixed 3 SMPS, an Allen organ power supply, a Peavey amp, and an HDTV converter. The Allen, the old leaky mains caps ( the 400 v rated ones) had blown a NTCR they used instead of a fuse on the 120 vac feed because it was cheaper. New mains caps & new NTCR fixed it. I also replaced all the other electrolytic caps, which were ~30 years old.
The Peavey CS800s, a leaky 47 uf cap on the 5 v control circuit had blown a 160 ma fuse. New fuse & cap fixed that. I also replaced all the electrolytic caps in that power supply since they were 26 years old. Note mains caps in SMPS are usually low ESR ones. I didn't replace any caps in the amp circuits; it still sounded good and had plenty of power.
A third SMPS I fixed was a Farnell HDTV converter. It got where it wouldn't work on cold mornings but did on warm days. 8 new electrolytic caps fixed that; I didn't change all of them. Of course the mains cap was probably the culprit, but I also replaced some of the 5 v supply & 12 v supply secondary caps. It was only 8 years old.
If the fet is blown (all pins shorted together), I've never managed to fix any SMPS like that. PC supplies. Fet takes out too many parts to be worth fixing.
Happy hunting.
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There is not much you can do without a power supply schematic and power supplies like this are normally beyond the knowledge of most techs.
Check you have power after the bridge rectifier.
If you have and nothing looks fried, check all of the secondary rectifier diodes for short circuit as that will put the power supply into its protect mode and just chatter.
WATCH OUT, if the power supply is dead, the main smoothing capacitors will stay charged up to a lethal voltage!
If the control chip is not oscillating, check there is a start up voltage for it.
Check you have power after the bridge rectifier.
If you have and nothing looks fried, check all of the secondary rectifier diodes for short circuit as that will put the power supply into its protect mode and just chatter.
WATCH OUT, if the power supply is dead, the main smoothing capacitors will stay charged up to a lethal voltage!
If the control chip is not oscillating, check there is a start up voltage for it.
Before focusing on the SMPS< PLEASE disconnect it from the power amp. Should be a 3 or 4 pin connector center of the power amp board, red and blue wires I think. Now does the thing power up and run the rest of the unit? A shorted output on a power amp channel is really more likely than a failed SMPS. The SMPS has self-protection circuits that shut it down of one of the supplies gets shorted out.
I believe you're talking about the large 4 pin connector I referenced in my original post. (The youtube video shows 51VDC per side but I get nothing).
I did test the other power supply outputs and get nothing except for one smaller 4 pin wire where the green and black wires show about 21VDC. Actually, I'm pretty sure that's the cable which lights up the Protect LED on the panel.
I did test the other power supply outputs and get nothing except for one smaller 4 pin wire where the green and black wires show about 21VDC. Actually, I'm pretty sure that's the cable which lights up the Protect LED on the panel.
Sorry, I didn't see any reference to pulling a connector in the first post. I just watched a few moments of your movie where you got 50v on each side of said connector. That suggests a working SMPS. I don't have sound on my computer, so I rarely watch the movies.
That is a reference video and not my own youtube video. Sadly, his power supply works and mine doesn't 🙁
OK, my speech...
SMPS are very dangerous, what may look like "ground" on the primary side schematic is actually not ground, it is -170v. The mains is directly rectified and filtered, so if you clip your scope ground to the "ground" in the switcher circuit, sparks will fly. Use an iso transformer to power the unit under test. Notice the different ground symbols for primary and secondary side, and note the primary side grounds are connected directly to the bridge.
MY general approach to these SMPS: Will it power up alone? Fan work?
I just go down the row and check all secondary side diodes for shorts.
As I read it, T2 is your kick start, so is there 60Hz on its secondary and is that little supply happening? That low voltage supply gets the IC running, to drive T1 and the main switching circuits. Once that starts the bottom winding on T3 takes over to power the IC.
SMPS are very dangerous, what may look like "ground" on the primary side schematic is actually not ground, it is -170v. The mains is directly rectified and filtered, so if you clip your scope ground to the "ground" in the switcher circuit, sparks will fly. Use an iso transformer to power the unit under test. Notice the different ground symbols for primary and secondary side, and note the primary side grounds are connected directly to the bridge.
MY general approach to these SMPS: Will it power up alone? Fan work?
I just go down the row and check all secondary side diodes for shorts.
As I read it, T2 is your kick start, so is there 60Hz on its secondary and is that little supply happening? That low voltage supply gets the IC running, to drive T1 and the main switching circuits. Once that starts the bottom winding on T3 takes over to power the IC.
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I'd have done 3 simple checks by now, a couple of days later.
First, mains caps are 0 volts. Use a clip lead for the negative probe of the dvm, one hand at a time. If not, discharge with 2 clip leads and a resistor. The mains caps are the big ones with the 200 v (cheap) or 400 v (quality brands) rating on the side.
After that, with line cord unplugged & power switch on, ohms (diode scale) from line cord hot to main cap +. Should be 1 diode drop, or about 600. Then from line cord hot to main cap negative, also 1 diode drop. Of course you reverse the + & minus probes for the 2 tests. An NTCR in one line or the other can run the resistance up some, but it won't be 9999 or open.
If you get ---- or 9999 or whatever your meter says is open, then your over aged mains caps took out the fuse, or whatever cheap part fender used instead of a fuse. Allen used an NTCR. Fuses are more expensive than the manufacturing cost because there are tort lawyers slobbering to sue the manufacturer, and liability insurance to protect the fuse manufacturer, involved.
Overaged cap, simple, replace them and find the blown part from line cord to cap and replace that.
If that is not wrong, test jonsnell's thesis, the secondary diodes blew. They are 3 legged devices on a big heat sink, and should be 1 diode drops from 2 of the legs, input, to the output leg. These are probably schottky diodes, 300 mv drop instead of 600-700 for the main AC diodes.
Not those problems, report back. May be too much for me to figure out, but test 1 or 2 failed on 2 of my smps. The 3rd smps had cold weather disease, which I've seen in smps at work, which usually were accompanied by a big puddle of cap slime in the bottom of the enclosure. (*****y 3 phase motor drives, SCR brand).
After seeing enzo's post, I'm too much of a klutz to work these things with the power connected, and I certainly wouldn't connect a scope to one. I use a totally isolated DVM, and I disconnect them from the AC to work on them. That doesn't fix it, into the garbage with it. Fortunately, mains caps takes out 90% of the ones over a few years old. The SCR brand motor drives at the factory would blow the mains caps at 4 years; that company is now no longer supplying Heat & Control as a result. 15 to 20 years from the peavey was very good; also the 20 years of the Allen organ supply. The 6 years I got out the mains cap of my farnell HDTV converter is about average for consumer grade gear.
First, mains caps are 0 volts. Use a clip lead for the negative probe of the dvm, one hand at a time. If not, discharge with 2 clip leads and a resistor. The mains caps are the big ones with the 200 v (cheap) or 400 v (quality brands) rating on the side.
After that, with line cord unplugged & power switch on, ohms (diode scale) from line cord hot to main cap +. Should be 1 diode drop, or about 600. Then from line cord hot to main cap negative, also 1 diode drop. Of course you reverse the + & minus probes for the 2 tests. An NTCR in one line or the other can run the resistance up some, but it won't be 9999 or open.
If you get ---- or 9999 or whatever your meter says is open, then your over aged mains caps took out the fuse, or whatever cheap part fender used instead of a fuse. Allen used an NTCR. Fuses are more expensive than the manufacturing cost because there are tort lawyers slobbering to sue the manufacturer, and liability insurance to protect the fuse manufacturer, involved.
Overaged cap, simple, replace them and find the blown part from line cord to cap and replace that.
If that is not wrong, test jonsnell's thesis, the secondary diodes blew. They are 3 legged devices on a big heat sink, and should be 1 diode drops from 2 of the legs, input, to the output leg. These are probably schottky diodes, 300 mv drop instead of 600-700 for the main AC diodes.
Not those problems, report back. May be too much for me to figure out, but test 1 or 2 failed on 2 of my smps. The 3rd smps had cold weather disease, which I've seen in smps at work, which usually were accompanied by a big puddle of cap slime in the bottom of the enclosure. (*****y 3 phase motor drives, SCR brand).
After seeing enzo's post, I'm too much of a klutz to work these things with the power connected, and I certainly wouldn't connect a scope to one. I use a totally isolated DVM, and I disconnect them from the AC to work on them. That doesn't fix it, into the garbage with it. Fortunately, mains caps takes out 90% of the ones over a few years old. The SCR brand motor drives at the factory would blow the mains caps at 4 years; that company is now no longer supplying Heat & Control as a result. 15 to 20 years from the peavey was very good; also the 20 years of the Allen organ supply. The 6 years I got out the mains cap of my farnell HDTV converter is about average for consumer grade gear.
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