2x QSC 3500 amps no power up?

[Ziinda]

I got 2 QSC series 3 3500 amps about 1 month ago and I ended up setting them up for home use connected through a dbx 2 way crossover. One for high and the low frequency. I had a set of speakers that I have been using for quite some time with other amps and have had favorable results no matter what amps were used. The bass drivers were mismatched and I got 4 new 8 ohm 8' woofers to replace the old ones.

After replacing I noticed 1 side had a sound that was similar to 1 driver out of phase, I removed a driver and checked wiring. All was good, turned if on again and same thing. Changed XLR cable from left to right and still was in the same right side. Changed the speaker outputs left and right and it was now in the left side.

Since I have made my own XLR cables and made custom XLR to RCA to use a NAD or Rotel pre amp as source, I checked all XLR cables to be sure they were all wired properly and all wires were still making contact. It all checked out good. I made another set right away just
to make sure since I had some new cables to work with.

Now this was all bring done at 4am and I live in a condo so you know I wasn't cranking it up and especially since I noticed an issue, I barely had volume audible to do testing. So after everything was set up and all drivers put back in, I hit the power on both amps and nothing lights up on either amp? I had a long night and figured it must be a power strip that turned off or something since I use 2 separate strips from 2 different circuits I had a hard time believing that but went to sleep to look into it later.

I checked all power and everything was fine, tried the amps again and still no power? Replaced the amps with the 2 that I was using prior to the QSC and everything was back in business.

I took a look inside the amps and found no fuses and no obviously burnt parts. These amps have huge transformers and small left and right modules that are made to easily be replaced if needed. There is nothing showing damage and I even tried moving modules to see if there was any chance of getting one going but no go.

So I have 2 amps die at the same exact moment that previously had no issues, I replaced the woofers from mismatched 4 and 6 ohm on one side and 3 and 8 ohm on the other. The amps had no problem running them like that with all drivers wired parallel so amps saw more than 2 ohms which the amps are rated to do. Plus I never cranked them into anything close to clipping since my speakers are rated at 200watts.

I have studied the boards and can't say if they have anything bad, I'm not familiar with transformers and how to do a proper test other than obvious short circuit. But how can they both die at the same time when they ran separate drivers fed from an active crossover and both old amps are still working fine?

I can't believe that both transformers went out at the same moment, these amps are supposed to be built to last but I noticed that one board had some repairs done. Without any fuses, what else can cause no power on other than bad transformers? From what I've read transformers rarely ever fail in audio amplifiers, no matter what brand they are. Plus both failing at the same time is not believable.

Anyone have no power issues with QSC AB style amps before? Please let me know what you did, even if you tossed them in the trash I'd like to hear back. It's my understanding that QSC sre supposed to be long lasting problem free amps and I'm not seeing this to be very true after my very light and very short use of their amps.

I also have another amp issue involving a Lab GRUPPEN C series amp I traded for knowing it had a fault on 2 out of 8 channels. I took a look and saw 2 bad fuses, replaced them and powered it up with nothing attached and it now does not power up at all, I haven't removed those fuses yet and tried it. The lab gruppen was never installed and was tested on a separate circuit on my bench. The fans used to come on and it showed a fault on channels 4 and 5, I never even connected anything to it, I turned it off and on many times before replacing the fuses. It made no noise, no lights, nothing after fuses were replaced and the fuses still test good right now?

This LG problem is not related to the QSC problem since they were never operating on any of the same circuits and the LG was never even connected to anything ever. I have read all literature on both amps and everything on line about these and everyone says they're both bullet proof and great amps. I have found this to be quite the opposite.

What is the average price to get an amp fixed? I've already ordered a few brand new amps and they work perfect, albeit they are only 250W x2 but still have similar sound and more power than I'll probably need. I just cant see tossing 3 amps in the trash if they have a chance of being repaired for a reasonable amount, keep in mind I only paid $160 each for replacement amps that have no noise other than slight fan noise and they seem to have good low frequency response, they are not rated below 2 ohms and are not bridgeable either. The QSC are rated to 2 ohm easily and put out 800 watts per channel or more. Currently looking at a crown com-tech 1610 locally for $100, it's rated 830w x2 into 4 ohms.

Any input on anything I have posted here is welcome, even if you have nothing good to say about any of this you just might get me thinking enough to figure something out!

Just so you know, I have tried out other lower wattage home amps and used a few older stereo receivers amp sections out without any problems other than heat related due to the low impedance of my speakers (volume was comparable and sound is identical as big amps) and don't want to burn up any of my classic receivers when I can avoid it.

 

[Ziinda]

If anyone else has this problem, the people at QSC told me to get new amps. (I asked them just in case it was something very easy and I may have overlooked it.)
After letting them sit for a month I decided I'd take a look inside and had a schematic handy, I was tracing the power wires and git back to the front and there's 2 switches, the LEDs and a pile if wired all bundled up there. I was trying to see under them but I couldn't, I got angry and bent the metal plate that everything is popriveted to and saw able to see down through the wires and low and behold there's a safety switch unlike anything I've ever seen before. It's a terrible design but what they did was mounted the switches so there is a screw of sorts that goes through the front panel and closes the switches through a hike in the front of the switches. Now I saw those ugly screws and thought WTF? It looked out of place and was baffled as to why they were even there. What had happened was those screws (which should have just been pins molded onto the front covers) were not the original and they had a nut behind them since they didn't thread in the holes. The openings on the switches are actually smaller than the holes in the front do some custom screws were needed. Grinding down the tips of the screws and using large enough to catch threads fixed it up. It was just due to all the moving around, the front covers needed to be tightened up too. But those switches only have about 1/16” from closed to open.
I have to say I was happy I fixed them but pissed that I was not informed of what I was exactly asking about to begin with. You think being a tech that he didn't know about those switches? You know he did, he just didn't tell me hoping I'd buy new amps. Really a dick move I thought, I wrote him back telling him exactly what I thought and he never replied back! I'm still shocked that he did that when it was such an obvious fix.

I have to say that thise amps have been incredible fir the last 4 months, absolutely silent (once I made custom XLRs fir the entire system). I would really like to pick up one of the 3800 series 3 amps, I believe it's their biggest air cooled amp they ever made, the 3500s are 1 step down. They get used heavily and never get hot even after bring left on for a week. 35+ years old and dead silent. Transformer hum was eliminated by tightening up mounting screws and positioning them after sliding them around untill it was gone. Strange but never hear anything other than a slight click when powered up using some 1875 watt remote outlets paid $16 on Amazon for 5 programmable outlets with 2 remotes with 5 on and 5 off buttons. It was the final touch on the system.

 

[whoaru99]

I've worked with the QSC folks before. Found them very helpful; anything but dicks. But, I understand why they would not respond to a dick.

(and, yes, a QSC 3500 is one of quite a few pro amps I have, most of them being QSC and a few Crown scattered here and there)

 

[eiraved]

If anyone else has this problem, the people at QSC told me to get new amps. (I asked them just in case it was something very easy and I may have overlooked it.

Maybe not all, but someone there gave @Ziinda some bad advice.

 

[whoaru99]

Maybe not all, but someone there gave @Ziinda some bad advice.

QSC is a commercial sound reinforcement company, not a hobbyist endeavor. Their advice was well intended in consideration of long term satisfaction/show must go on, rather than potentially putting money into old amps, not a "rip off" suggestion per se.

 

[eiraved]

the people at QSC told me to get new amps

QSC is a commercial sound reinforcement company, not a hobbyist endeavor. Their advice was well intended in consideration of long term satisfaction/show must go on, rather than potentially putting money into old amps, not a "rip off" suggestion per se.

If the intended goal was to have you purchase another QSC amp, then the advice was sufficient. I would think directing the individual to contact QSC Service & Repair or direct them to an authorized QSC service center would suffice IMHO.

 

[whoaru99]

If the intended goal was to have you purchase another QSC amp, then the advice was sufficient. I would think directing the individual to contact QSC Service & Repair or direct them to an authorized QSC service center would suffice IMHO.

Or, the OP could have consulted the Series Three Owner's manual rather than accusing QSC of witholding vital information for nefarious purposes.

 

[eiraved]

Or, the OP could have consulted the Series Three Owner's manual rather than accusing QSC of witholding vital information for nefarious purposes.

Or maybe the OP could have avoided the less than stellar QSC service and asked you directly.

I'm not saying the QSC technician had a "nefarious" purpose in telling the OP to forego repairs and just buy another QSC amp, but it definitely wasn't the correct response. Good customer service is the quality and timely assistance provided by a business and its employees in solving the customer's problems. Customer service professionals are responsible for ensuring customers have a good experience by fulfilling their needs. Unfortunately, the QSC technician did not follow this standard with his response to the request for assistance. We also see the results of his advice by the OP's response to his solution. Not a good way to do business.

For the record I am not a QSC hater, having owned several QSC amps as well and I like the product.

 

[whoaru99]

Or maybe the OP could have avoided the less than stellar QSC service and asked you directly.

I'm not saying the QSC technician had a "nefarious" purpose in telling the OP to forego repairs and just buy another QSC amp, but it definitely wasn't the correct response. Good customer service is the quality and timely assistance provided by a business and its employees in solving the customer's problems. Customer service professionals are responsible for ensuring customers have a good experience by fulfilling their needs. Unfortunately, the QSC technician did not follow this standard with his response to the request for assistance. We also see the results of his advice by the OP's response to his solution. Not a good way to do business.

For the record I am not a QSC hater, having owned several QSC amps as well and I like the product.

Unfortunately we have only the OPs side of the story.

In the OPs assertions they are not very reliable or long lasting amps amongst other things, knows they're approaching 40 years old?

 

[zinda]

What I'm saying is exactly what happened, if you'd like I can post the entire conversation that we had in 3 emails. 1st is me asking what could have happened since both were working then both stopped. That's what really confused me? So that's why I figured I'd ask around since I only had the amp a few weeks and my system had undergone quite a few changes due to my move to biamp then to triamp my speakers. I've done my share of repairs over the years but this had to something I was overlooking so I reached out.

He immediately suggested new amps and said the manual was available which I already had a copy. Now when looking through the manual it dies refer to removing the modules. But I was trying to avoid taking it apart so that part really wasn't pertaining to an amp that was together and was not taken apart. The problem comes in, since you were able to find that blurb in the manual why didn't a tech suggest that exact thing to me knowing all the time that it's most likely the issue?

I did mention that while moving it by the handles it did cut out and comeback on a few times, but that could have been the power cord moving in my power strip since it's right behind it. That's happened before so I didn't think much of it.

The thing I found unusual was that the front plates didn't have that protrusion molded right into the casting? Why a screw or in my case a small bolt with a nut behind it. It looked so out of place and when I checked behind it, all I could figure was there must be something missing. There is nothing to screw into, the switches are hidden behind a shield an inch away from the front cover at the bottom edge of the frame. There did not seem to be any purpose for the bolts and I even replaced the boots with a shorter one that threaded into the hole before I decided to rip them apart and take a closer look.

One more issue I had was while trouble shooting it, I first studied the schematic and if you do the same you will not find that switch shown! That's the thing that really pissed me off. I only found it while physically tracing the wires, plus it's so hard to see and the metal is welded together around the switch which is mounted to the bottom plate with just a hole in the cover plate which also holds the LEDs and power switches.

Finding it was very unexpected even though I read the entire manual, there is no drawing or depiction that readies you for a switch in that location or of that type. It looks like no other switch I've ever seen and I have a box full of them from stuff I've torn apart and salvaged parts from, knowing that switches are a main source or failure. Both power switches tested good. That's when I finally bent the plate out of the way thinking there was some hidden circuit breaker. That's then only reason I found it was due to anger.

So when a company makes a drawing showing the circuits but leaves out the main power switch it makes it difficult to understand why s tech wouldn't tell me especially when I told him I felt that there is something very simple that I'm not seeing and that's the only thing I wanted to know. Am I missing something it feels like there's a simple reason both amps stopped, what do I need to know about these amps that would do this?

That's why I think he was being a dick, all he had to say is there's a normally open safety switch hidden inside the case that requires that bolt to touch it and hold it closed, make sure the bolt is long enough to press on the switches. That's a typical problem that happens when the front covers come loose or bent. It's not shown in the schematic buts it's mentioned briefly in the manual under removing amp modules.

That would have been the correct non dick answer.

Both amps work great, I'm not knocking the company just one guy!

 

[zinda]

When I emailed back that I had found the issue and both amps work fine, I asked why he didn't tell me what to look for especially when I was asking him if it was something very simple that I was overlooking?

He did not reply back! That's when I drew my own conclusion. If anyone thinks he did the right thing I would have to say that you were the guy I was asking, because he did not help me in the least in fact those amps sat for weeks while I shopped for replacements I spent money on another amp that I eventually used to power my tweeters but I have a pile of amps that are both working and need repair. I was looking for another good amp which I really didn't need to do.

I really should sell my broken stuff to someone that has interest in fixing them. I have a LabGruppen C80 200Wx8 had 2 channels with faults, replaced 2 fuses then it wouldn't power up at all. Peavey CS400 no power up. One day turned on then off, never played it loud worked fine for 6 months till now. Sonus 60Wx2 one quiet channel.

 

[whoaru99]

Frankly, your continued assertion the tech knew all along it was the interlocks but withheld the information is way out there. If he was intent on witholding information he wouldn't have provided the manual.

One might possibly argue he should have known but, remember again, the amps are nearly 40 years old. And, based on the symptom both failed at the same time, it's not really logical to suspect "failure" of the same part at the same time in two separate amps. I would not have thought to suggest the interlocks straight away based on two simultaneous failures.

But, you are convinced QSC was trying to rip you off so nothing I say is likely to change your mind from that. I don't believe that for a second and never will.

Might it be a case of less than stellar support on a ~40 year old amp? Maybe... but he did give you the best documentation available, lacking as it is (schematic starts at transformer primaries, not the power cord, therefore interlock is not shown on schematic).

 

[whoaru99]

For anyone more curious (or perhaps for posterity sake) about the infamous interlock switch, it's circled in the first photo below. It resides behind the front panel of the amp. The hot lead of the mains cord leads directly to it.

The screw that operates the switch (on the later models like mine) is shown in the 2nd photo below.

The reason for the interlock switch is the modular nature of the amp. With removal of just a relatively few screws the front panel comes off to faciliate sliding out the entire left channel or right channel amplifier module for quick replacement. The AC mains power switches and circuit breakers are right behind the front panel so the interlock cuts the supply to all that when the front panel is removed. (additional info: it's a dual mono amp with separate power switch and breaker for each channel).

 

[eiraved]

I really should sell my broken stuff to someone that has interest in fixing them. I have a LabGruppen C80 200Wx8 had 2 channels with faults, replaced 2 fuses then it wouldn't power up at all. Peavey CS400 no power up. One day turned on then off, never played it loud worked fine for 6 months till now. Sonus 60Wx2 one quiet channel.

You should become a Subscriber so you can sell these items on BarterTown.

 

[zinda]

You should become a Subscriber so you can sell these items on BarterTown.

I wouldn't even consider shipping anything as heavy as those amps. I'm going to post them locally and also on 2 other used gear platforms that get a large enough number of views that I might be able to sell them or trade them.

I was looking for a better active crossover recently since I outgrew my old DBX 2 way and I was having some strange issues with my JBL 3 Way. I had my eye on an old Rane 3 way that I saw posted locally fir 6 months and I sent a message that went unanswered for weeks, I replied back saying I was interested and when could I see it. No reply fir months! I sent another message with a reduced offer and they replied quickly. But never gave me any definite date. 2 more weeks and I saw their post was reposted. I asked if I could come by they agreed I went there t day and I bought it and a BBE maximizer but as I was leaving I noticed it was the 2 way model. I went back and asked where is the 3vway and they said they just sold it! Well I had no use for the 2 way and they refunded my money.

Then spotted a deal for new behringer 3 way and even more what I needed was a 3xwsy with a bunch of EQs, programmable everything with delays etc. Now I tried a miniDSP and another Brazilian made digital crossover thing and both of those were complete garbage. 1 was making a grating noise when I turned on my mid amp. Tried twice and it was still there after new cables etc? The other even when in full bypass mode was altering the sound so much it was degrading it to about a speaker inside of a lunch box. I knew I'd have to pay more to get anything that was usable. The best behringer with all the bells and unusable whistles RTA and auto tune was if course sold out and they said a month wait. I was fine with that and picked up a regular analog 3 way in the mean time.

A week ago I spotted a rare demo unit posted and quickly bought it while I had the chance. Next day I'm looking at the piece description and see it's actually an elaborate EQ auto tune UKTRACURVE PRO DEQ2496 not the DEX. So I figured I'll check it out and see if I can make it work. First attempt at auto tune required me to turn up my system higher than it's ever been to be able to even run the test? I couldn't help but think what good is this tune going to do when I'm never going to listen at this level, but I needed to do a run to make sure it worked.

2 minutes later I looked at my tweeter amp and the lights are ful red no blinking at all. I look at the RTA and switch to the next page that shows the sliders moving and I'm looking for the sliders. I see 8 or 9 at the highest side are maxed and then the next 15 are minimum! I immediately turned it off and I sends a very nice super loud pop through my entire system that made me jump. Now I could smell what I thought was burning paper! Right near the system. Convince that my tweeter amp had something super hot I took a closer look and smell but it was fine. Today I remove the behringer stuff and put my old pieces back and low and behold the right side electrostatic tweeter/mid was the part that burned up! So now I'm looking into what I need to repair the electronic part of it and will need to swap out those stats for another set I was using. Let's just say I'm not really happy with my sutotune. Sounds very unbalanced and smelt like burning paper while a jet 3ngine was running inside my living room during testing.

Good thing I was only running the test on the right side speaker. Behringer no longer will be considered to hold a place in my system. I've been using an old AZDEN 2/3 Octive eq that Has an RTA, pink noise, pure tone generator with sweep or selective tones and a mic input that can run the tests at any volume I choose and the entire process is completed in 10 to 20 minutes. I also have a dual 31 band EQ that I'll use for fine tuning and run it through a tape Mon loop so I can select it or the AZDEN or neither. I find very little nee to do much eqing at all. Just a bit to boost the 2 highest frequencies. A peak at 2k and a dip at 500 (that's near the low mid drivers are crossed. Then a small boost at the last 2 lowest frequencies make it look really steady across the RTA on the EQ and I've checked a few apps on a bunch of tablets and phones which all look very similar to what I'm seeing as well as a computer RTA which is how I found out my behringer 3 way was picking up tins of static and hum from my ac mains computer switching power supply! Removed the ecwsy and dead silent.

I learned the hard way that digital DSPs are more of a headache than anything else and I'm not caring to hear about hiow much of an improvement others have heard because I have to wonder just how awful it sounded prior to using the device? Mine sounded great and would have been shocked if it could sound any better but at the same time I needed to know if it was possible and if it was I would have been thrilled to hear it. But as I suspected none have done anything but waste my time and now my money!

Those amps can dish out the power and I knew it was bad to ever turn it up that loud. I've never burned out a tweeter in my life, I have ended the life of a few midbass that were junk to begin with but I knew they had no business acting the part and was not surprised to see them fail quickly. I have much to do now.

 

[Ziinda]

I wanted to add to this post after owning these amps for several years now and ive had an issue with 1 channel running hot and in need of a bias adjustment. The service manual runs through a bunch of tests and ends up with the bias setting at the end. This requires test equipment that is really not used now and i havent found anyone who is willing to set it for me claiming the amp probably has other issues. I have tested each component and found nothing wrong so i decided to go about setting it myself.

One channel was running hot and would occasionally show a blinking red LED while idle and once it started amplifying again it would turn green. I tried adjusting the 3 pots on the board to see exactly how they affected the voltages across the resistors connected to them and could not get much change so i removed the pots and tested them and found some inconsistency in their linearity even after deoxing. I replaced the 2 higher ohm pots with similar and the 100 ohm pot was untestable since it had a capacitor across the 2 output leads and after consulting the service manual i found the manual reproduction shows a device labeled HH 14 which there is no such device and compared it to the other schematic (there are 2 since they made an early model an a later model) that part is actually a Resistor number 14 but its a thermistor with a 50 ohm rating) and see its a thermistor with a 50 ohm rating and saw my pot has a 238picofarad cap with a 100v rating! I removed the cap and set the bias to where it now works without any issues but im getting a thermistor for it since its required for balancing. The part looked like it was a stock part and never considered checking it until now. Amp has been running for the last few days idle and never got hot, today i will check the rail crossover distortion if possible using an o scope on the outputs.