Power-up the unit. Very low volume even with the gain turned-up. suddenly we hear a pop and crackel sound (like there is a loose connection). All connections examined and found to be fine. Try a mic in all channels, very low volume; like no power. Suddenly, red overheat light goes on and unit shuts down. It appears that only half the amp is working. if there are two amps, then one is defective somehow. this would account for the low power and the "crackle" from the speakers. The unit was used only two times as PA for small group of attendees at a seminar. Any suggestions? Thanks
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Re: Fender passport model # 250 Used Only Twice!
Go back in and find where the electrolitic capacitors connect to the board. They look kind of like a battery. One or both of them have broken loose from the main board, preventing any significant current from going to the output transformer, and causing overload. This is a common problem, and it does not take much rough handling to cause it.
where the break is is at the solder connection. Under a magnifying glass, the break will look like a little circle. Float fresh solder on that or any other large solder joints which may be cracked or broken.
Use standard precautions when working around high voltage.
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A shorted speaker cable could cause this... however, what you do is to replace the fuse BUT wire a 150 Watt lamp in series with the power input... This acts as a resetable fuse for testing. If the lamp stays lit, you still have a failure.
You are in danger of popping the amp. The Fender passport 150 would be capable of covering about only a 20 foot by 20 foot area. If your area is bigger than that, you need more power and certainly bigger speakers. I would NOT recommend the larger Passport systems as the speakers are too directive for what sounds like your use... also there are reliability issues.
Turn down the VIP knob and try it. This is on channel 1 for announcement voice overs overriding everything. It has a threshhold setting for adjusting that. Here is the manual for it. http://support.fender.com/manuals/pro_audio/Passport_P150_manual.pdf
I have answered some of this before, however I have reveiwed the schematic and as an electrical engineer I want you to do a couple tests.
First, plug in a set of headphones into the preamp out jack. Note that due to the impedance mismatch what you hear will not be very loud. Now change the state of the clean OD. Did you hear a faint pop?
Next plug a LOW impedance device OR even an instrument cable into the power amp "input" jack. Do this with the power off then warm amp up.
Now, change the state of the clean OD. Did you hear a faint pop?
Now for the analysis. If you did hear one in the first test and NOT in the second, the pop you are hearing is the "NATURE OF THE BEAST".
I can tell you from the design that the pop you hear is from coupling within the clean and OD relays within the unit. There is no cure for this within the unit other than find another brand...
I would recommend that you use an EXTERNAL pedal for the effects you want rather than trying to use the clean OD in this amp. I suspect it was never intended to be shifted during playing as I can guarantee it will pop when you shift while having anything other than dead silence (not even a bit of hum from your guitar). There is also statistical noise in the preamp that the laws of physics will not let us get around that may be enough to create a bit of a pop.
You could also use a volume pedal between the preamp output and the power amp in to throttle the volume to zero before shifting to OD.
In general I think you will find that what you are hearing is the nature of this beast.
1) can happen if the speaker is dying - voice coil defective or magnet needs recharging. happens sometimes with low quality speakers.
2) faulty pre-amp section can reduce overall gain resulting in lower output volume. 3) for old amps dry solders in pre-amp & power amp section can have the same effect. 4) faulty coupling and filter capacitors can severely effect frequency response too.
It seems like the speaker jack tip needs cleaning, or the contact has become bent away from the connector and needs to be re-aligned. The Passport is a portable system, so after years of plugging and unplugging the speaker jacks may be worn. Try using the "Stereo 2" connectors. You can also try cleaning the jack with electrical contact cleaner, and. a cotton swab.