Fender PA problem. Passpoprt 250

[DaCentaur]

Just wondering if I could bump this back to the original question of power amp tx? I have the same problem with a friends passport and I am a decent electronic tech but unsure if I can trust my meter readings of these while they are still in the circuit. How should I check these Enzo? Thanks so much!

[Enzo]

Not sure what you are asking. If transistors measure shorted, remove them and test them alone.

[DaCentaur]

Not sure what you are asking. If transistors measure shorted, remove them and test them alone.

Not sure how to measure them for shorted on the board. can you tell me which legs to measure together and what they read? thanks

[Enzo]

Don't overthink it. Each transistor has three legs. If any are shorted together, there is nothing external to the transistor that will hide that. SO right where they sit, probe their legs with an ohm meter. Three legs, three combinations of two. If any two legs appear to be shorted together, remove the part and test it again while it is out. Something else in the amp could be shorted and making the transistor seem so, that can happen, but the reverse won't. The amp can;t hide a shorted part.

A short - a short circuit - two things connected together that should not be. On the meter? Zero ohms, or close to it.

[pecorporation]

Awesome.

[DaCentaur]

thanks...

Don't overthink it. Each transistor has three legs. If any are shorted together, there is nothing external to the transistor that will hide that. SO right where they sit, probe their legs with an ohm meter. Three legs, three combinations of two. If any two legs appear to be shorted together, remove the part and test it again while it is out. Something else in the amp could be shorted and making the transistor seem so, that can happen, but the reverse won't. The amp can;t hide a shorted part.

A short - a short circuit - two things connected together that should not be. On the meter? Zero ohms, or close to it.

Finally got a chance to look at this thing again..the only ones that appear to be shorted is Q230 and Q232. Would those cause it to go into Protect mode as well? Hoping to find out before i go ahead and desolder them from the board. Thanks!!!

[DaCentaur]

Finally got a chance to look at this thing again..the only ones that appear to be shorted is Q230 and Q232. Would those cause it to go into Protect mode as well? Hoping to find out before i go ahead and desolder them from the board. Thanks!!!

Actually after desoldering it was just Q232. Would this cause the Protect mode...thanks again

[Jazz P Bass]

From what I can tell from the service manual, Protect is engaged when a voltage drop is sensed, on the power supply.
So, yeah, if the voltage were to drop from a shorted output transistor, Protect would engage.

[rrflorida]

Protect Mode

My PD 250 is stuck in protect mode (purchased it this way...)

After reading through this thread, measured the power amp transistors, none appear to be shorted. Disconnected the power from the PA board (CN17), still in protect mode. Not sure what to do next. Any advice appreciated (I'm not a technician, so type slowly

Thanks much
randy

[52 Bill]

My first guess would be that you have a short in the power supply. Be very careful as this has a switching power supply that can do you some real damage.

The first test that I do is to check all of the diodes in the power supply. Unplug the supply and check to see that the caps have discharged. Then use the diode test function on your meter to test the diodes.

[rrflorida]

Thank you for the quick response Bill. I'll give that a go and report back.

[Jazz P Bass]

You really, really should start a new post
Etiquette and all that kind of stuff.

[dbjacobson]

Hi, I am in Ft. Lauderdale, FL and see all these posts re: your Fender Passport P.A. - I also obtained one, the PD-500 model - in an as-is state where all power lights light up but it instantly goes into protect mode and therefore has no sound. Did you ever get yours fixed and if so, how did you do it? Obviously, these Chinese built POS heads were built so poorly for so many units to have the same exact problem!!!! If there are any shops here who can fix them, please contact me.

[Enzo]

Hi db.

You have made a faulty assumption. WHen a singing group or a sales manager or an auctioneer or whoever buys one of these and it works, he doesn;t go on the internet and rant about it. You only see the people who DO have problems.

We may have ten threads about Passports, but that doesn't take into acount the tens of thousands of them that work just fine.

These systems have SMPS - switchmode power supplies. One characteristic of the SMPS is that it protects itself. If one of the amplifier channels is blown, it won;t start up. If the mixer section has a shorted IC< it won't start up. And indeed, if the SMPS has a shorted rectifier, it won;t start up. SO we often see the complaint that the amp won;t leave protect. It is easy to assume that the "same thing" is happening, but in reality, just about anything that DOES go wrong will result in a non-start condition.

It is not unlike the national news. The FDA will go into crisis mode when there is a breakoout of listeria or something. We find that 30 people are critically ill with it, and they are looking for the source. Now that is serious, I'd agree, but it overlooks that 300,000,000 of us did NOT get the listeria. Point being that a lot of stories about it in the news doesn;t mean the food chain is in shambles.


I know we outlines some troubleshooting in some of the threads. DO those things. Disconnect the power amp to see if it is responsible. DIsconnect the mixer section. and if teh SMPS itself alone refuses to start, then I'd be looking for shorted rectifier diodes in its secondary.

[bwinkel67]

Hi, I am in Ft. Lauderdale, FL and see all these posts re: your Fender Passport P.A. - I also obtained one, the PD-500 model - in an as-is state where all power lights light up but it instantly goes into protect mode and therefore has no sound. Did you ever get yours fixed and if so, how did you do it? Obviously, these Chinese built POS heads were built so poorly for so many units to have the same exact problem!!!! If there are any shops here who can fix them, please contact me.

Hi db,

First off, Enzo is a great resource, he helped me tremendously. I fixed it myself and I believe that part of my problem was that I kept buying counterfeit power transistors (on eBay from Asia)...I finally bought a set of authentic ones and replaced an entire channel's worth. I also biased the board (using a technique that Enzo pointed out) but found out it was already biased so I believe the fake replacement transistors did me in a few times (otherwise it's pretty darn easy to fix the thing).

The big question was why it blew on two separate occasions over 18 months apart, having been used once a week for 3 hours...aside from it blowing continuously while being fixed due to the aforementioned counterfeit transistors. I couldn't figure that out but decided to buy an inexpensive mixer (BEHRINGER 502 5-INPUT MIXER WITH XENYX MIC PREAMP on eBay ~$35 w/shipping) and it's made a big difference in that the volume now on the Passport is run at around 2 on both channels so the we are not driving the amp very much...might be a good idea to use as an add-on with these systems since they seem to blow when driven too hard.

(FYI, we used it to DJ a dance where most people plugged laptops and/or laptop add-on sound cards into the unbalanced RCA inputs...some of these cards may not have been outputting a high enough signal which caused the amp to have to drive the signal and perhaps that's what stressed the transistors to where they blew...we did have a fan blowing on the heat sink during the 18 months we used it, so if it overheated it really must have overheated.)

TM