Anyone up for a challenge? Definitive Technology BP2000 amp repair

[DEFTECHY]

Tried searching for this subject and dont really see anything pertaining to repairing failed amps on these older BP2000tl series speakers, just wondering if anyone on here has attempted to repair these amps or know of an audio repair shop/tech that can work on them. I have repaired the humming issue on the later 7002/7004/7006 amps with success but those amps are a different design than the older 2000tl amps.

I have pulled the bad amp and found a few burnt traces and resistors, Im sure some failed output drivers too but havent got that far for removing/checking the output drivers or diagnosing other parts to find why the amp died. The other amp is working OK so I will probably use it to compare to the dead amp to see if I can find the problem. Probably a long shot for anyone on here thats worked on these amps but just wanted to start a thread for any info on repairing these amps. I may try to diagnose/repair it myself if I cant find anyone that can work on them for a reasonable price.

So far I have found some burnt or completely fried resistors and some of the very small & delicate traces are burnt too, I think I can repair the traces with jumpers and replace the resistors but will need to test the output drivers to see if they are bad too. Not sure what caused the amp to blow since the other speakers amp is working fine, probably a power surge or lightning strike or someone shorted the speaker wires? I will try to post pics later when I get the amp disassembled more to show the burnt resistors, until then, anyone familiar with these amps or up for a challenge to work on them or help me with what Im sure will be lots of questions? Im an amateur but have done basic diagnostics and repair of some older vintage amps like sansui & marantz, just successfully completed a full recap of a vintage AU sansui integrated amp, hoping I can get this one working again.

 

[drumbum]

You are ahead of the game with the other amp still functioning.
Should make it easier.

 

[robgmn]

What type of amp is that? I ask b/c I just replaced an amp on an older sub. Trying to chase a nasty turn-on "thunk", so I fully recapped it. The "thunk" stayed and shortly after, a new hum appeared. I gave up and simply dumped the amp in favor of a new one for about $98.
I figured no sense in putting any more money or time if it was going to reward me with cascading failures.

 

[DEFTECHY]

What type of amp is that? I ask b/c I just replaced an amp on an older sub. Trying to chase a nasty turn-on "thunk", so I fully recapped it. The "thunk" stayed and shortly after, a new hum appeared. I gave up and simply dumped the amp in favor of a new one for about $98.
I figured no sense in putting any more money or time if it was going to reward me with cascading failures.

Not sure what you mean by what type of amp, but its a 2 part amp/pre amp with mostly traditional parts, the amp powers the sub/woofer and the upper section of 6.5" mid woofers & tweeter are powered by the receiver or amp like normal speakers. I will post a pic of the amp section to show its design & the damage.

A new amp for a low price like $98 would be awesome... unfortunately thats not an option for these 20 year old speakers with proprietary amplifiers that are no longer made & no support from the company. As with lots of powered subs/speaker brands that use these internal amps, they were mass produced with lower quality parts on the amps so their life is on borrowed time before they have issues or just fail. Def Tech used to stand behind the speakers even years out of warranty by sending customers free replacement amps, but since they have been sold to one of those big mother companies that buy up multiple audio brands that used to have good service & quality, that is all but gone.

Hoping someone on here has worked on these amps or know who can... or if I try to work on it myself, some experienced members/techs can hold my hand to help with any questions or issues I run into.

Edit- added a few pics of the amp, it connects to the pre amp (not shown) via the ribbon cables, the heat sink sides come off pretty easy leaving just the PCB. The burnt resistors & traces are only on the top half of the amp with the big caps, there are 4 output drivers per half, the bottom half or section doesnt show any signs of heat or damage, this is a 1 channel amp powering a single 15" woofer.

 

[tarior]

Parts Express plate amp to the rescue! IMO/IME, without schematics/service info, properly repairing that amp might be a pretty tall order.

 

[robgmn]

Not sure what you mean by what type of amp, but its a 2 part amp/pre amp with mostly traditional parts, the amp powers the sub/woofer and the upper section of 6.5" mid woofers & tweeter are powered by the receiver or amp like normal speakers. I will post a pic of the amp section to show its design & the damage.

A new amp for a low price like $98 would be awesome... unfortunately thats not an option for these 20 year old speakers with proprietary amplifiers that are no longer made & no support from the company. As with lots of powered subs/speaker brands that use these internal amps, they were mass produced with lower quality parts on the amps so their life is on borrowed time before they have issues or just fail. Def Tech used to stand behind the speakers even years out of warranty by sending customers free replacement amps, but since they have been sold to one of those big mother companies that buy up multiple audio brands that used to have good service & quality, that is all but gone.

Hoping someone on here has worked on these amps or know who can... or if I try to work on it myself, some experienced members/techs can hold my hand to help with any questions or issues I run into.

Edit- added a few pics of the amp, it connects to the pre amp (not shown) via the ribbon cables, the heat sink sides come off pretty easy leaving just the PCB. The burnt resistors & traces are only on the top half of the amp with the big caps, there are 4 output drivers per half, the bottom half or section doesnt show any signs of heat or damage, this is a 1 channel amp powering a single 15" woofer.

Since the amp only powers to built-in sub, my $98 suggestion is still viable, or may be a $199 suggestion. depending on your receiver.
Post your receiver model and I'll share an idea if it could work.

 

[drumbum]

Not sure what you mean by what type of amp, but its a 2 part amp/pre amp with mostly traditional parts, the amp powers the sub/woofer and the upper section of 6.5" mid woofers & tweeter are powered by the receiver or amp like normal speakers. I will post a pic of the amp section to show its design & the damage.

A new amp for a low price like $98 would be awesome... unfortunately thats not an option for these 20 year old speakers with proprietary amplifiers that are no longer made & no support from the company. As with lots of powered subs/speaker brands that use these internal amps, they were mass produced with lower quality parts on the amps so their life is on borrowed time before they have issues or just fail. Def Tech used to stand behind the speakers even years out of warranty by sending customers free replacement amps, but since they have been sold to one of those big mother companies that buy up multiple audio brands that used to have good service & quality, that is all but gone.

Hoping someone on here has worked on these amps or know who can... or if I try to work on it myself, some experienced members/techs can hold my hand to help with any questions or issues I run into.

Edit- added a few pics of the amp, it connects to the pre amp (not shown) via the ribbon cables, the heat sink sides come off pretty easy leaving just the PCB. The burnt resistors & traces are only on the top half of the amp with the big caps, there are 4 output drivers per half, the bottom half or section doesnt show any signs of heat or damage, this is a 1 channel amp powering a single 15" woofer.

Have you ever dealt with surface mount components? It will be a chore if you have to remove a smd to check and replace if good. Got any old broken gear to salvage from?
You know how to check transistors, correct?

With a working amp it will be easy to identify burned resistors (as you can see the bands on the good and measure) and such. Traces are easily repaired with some wire,.....like telephone wire.

I would think the hard part is scrolling through pages at Mouser or Digikey to find the replacement parts or equivalents.

 

[DEFTECHY]

Parts Express plate amp to the rescue! IMO/IME, without schematics/service info, properly repairing that amp might be a pretty tall order.

PE plate amps are not an option for these speakers... #1 they wont fit the cabinet or the amp section if trying to replace the PCB from an aftermarket amp... plus the woofer in these older Def Techs are usually weird ohms, this is 75ohm... cant use any traditional amps that are 4-8ohms. But thanks for the suggestion.

I have a good working amp from the other speaker to use for parts identification & testing, only real concern is the small delicate traces that need repaired.

Since the amp only powers to built-in sub, my $98 suggestion is still viable, or may be a $199 suggestion. depending on your receiver.
Post your receiver model and I'll share an idea if it could work.

See above comment regarding other amp options... cant use any available aftermarket amps, especially cheap $100 ones for a 75 ohm woofer. But thanks.

I have a few different receivers from vintage to modern digital, but even with modern digital receivers with good bass management settings, no aftermarket amps will fit the cabinet or drive the 75 ohm woofer correctly. need to repair or replace with an OEM amp to do it right.

 

[tarior]

With any change in amp, you'll have to make an adaptor panel of some sort. As for driving a 75 ohm load, well, rotsa ruck!

 

[DEFTECHY]

Have you ever dealt with surface mount components? It will be a chore if you have to remove a smd to check and replace if good. Got any old broken gear to salvage from?
You know how to check transistors, correct?

With a working amp it will be easy to identify burned resistors (as you can see the bands on the good and measure) and such. Traces are easily repaired with some wire,.....like telephone wire.

I would think the hard part is scrolling through pages at Mouser or Digikey to find the replacement parts or equivalents.

Yes I have dealt with surface mount parts on another model of Def Tech amps that use them, not fun... but this board doesnt have any surface mount parts, or at least none that show damage, its just the burnt resistors, maybe some diodes and likely some of the out put transistors. Yes, I know how to test transistors, just recently repaired a vintage sansui integrated amp that had bad output transistors on 1 channel, replaced them & the other side to match, then did a full recap/restore & its working/sounding great! Learned a lot from that one & some other members on here in the sansui sub section.

Yes Im hoping to match up the resistors from the good amp and be able to fix the traces... but they are very small & thin compared to most PCB's Ive seen or worked on, so hoping thats not a problem.

Ive got pretty good at using digikeys search function for parts, had to identify & source 50+ caps myself for the sansui recap, most the BOM's for that amp were outdated or they wanted to charge a fee for it or changed parts from OEM which I prefer to keep original for things like this.

Hoping to find a tech that is more skilled than me to work on it for a decent price but Im willing to give it a try myself, will dig into it soon if no luck finding someone else.

Thanks for the replies.

 

[DEFTECHY]

With any change in amp, you'll have to make an adaptor panel of some sort. As for driving a 75 ohm load, well, rotsa ruck!

Actually some of the BASH amps at PE will fit some subwoofer cabinets without adapter plates, have done that before... but thats exactly why I dont care to use an aftermarket amp, plus the weird ohm of the woofer... dont need rotsa ruck driving 75 ohm woofer if repairing the original amp.

 

[tarior]

Finding someone who can repair that amp without service information will be a tall order. Finding someone who can do that, and do it for free or next to free? LOL.

 

[DEFTECHY]

I prefer to have a more optimistic view on this... I agree not having a service manual or schematic isn't a good thing, but I mentioned I have an identical working amp from the other speaker to work from, can match the burnt resistors and caps are easy to identify as well as the outputs once I pull & test them. I want to try to work on it if its just checking/replacing some resistors/caps/outputs, but if needed I can send the working amp with the bad one to whoever can work on it. Shouldnt be a tall order.

Never suggested nor do I want someone to work on this for free... I said I would pay a decent reasonable price for someone to work on it, LOL. These speakers still hold a good value in working order & they are in excellent shape otherwise, they are worth some time or money to repair.

 

[gadget73]

One nice thing about solid state amps is that higher ohm loads really aren't an issue, at least if we're talking conventional old style AB transistor amps. It puts more stress on the parts going low. The practical concern is power output. Watts is volts squared divided by the load, so an amp that makes 100 watts into 8 ohms is making 10.7 into a 75 ohm load. Unless its very efficient thats probably not going to be very satisfying.

Not the faintest clue what a high ohm load might do on a class D amp.

if I were designing an AB amp to work with high ohm loads, it would probably actually be two amps run in bridge mode. Double the voltage swing without double the power supply rail voltage or having to deal with finding high voltage transistors to deal with that.

 

[robgmn]

PE plate amps are not an option for these speakers... #1 they wont fit the cabinet or the amp section if trying to replace the PCB from an aftermarket amp... plus the woofer in these older Def Techs are usually weird ohms, this is 75ohm... cant use any traditional amps that are 4-8ohms. But thanks for the suggestion.

I have a good working amp from the other speaker to use for parts identification & testing, only real concern is the small delicate traces that need repaired.


See above comment regarding other amp options... cant use any available aftermarket amps, especially cheap $100 ones for a 75 ohm woofer. But thanks.

I have a few different receivers from vintage to modern digital, but even with modern digital receivers with good bass management settings, no aftermarket amps will fit the cabinet or drive the 75 ohm woofer correctly. need to repair or replace with an OEM amp to do it right.

Well, THAT sure puts a different paint job on things.
But not surprising to me from DT. Not after I waited 6 months for them to rebuild an amp from a Supercube 1 sub a buddy gave to me, only to find that with a 10" driver and two 10" passive radiators the frequency response dropped like a stone below 30Hz.

Something interesting someone posted about the amp you're dealing with (not that it helps you any): "Basically the power amp is a bridge arrangement powered directly from rectified mains, and is housed on a chassis separate from the backplate with preamp and controls. The only connection with the power amp is thru an optoisolator that carries PWM signal. Seems a lot of effort to avoid the cost of a beefy power transformer."

Good luck with your quest!

 

[Boonaroo]

I just had my Definitive Technology Mythos STS Super Towers sub amps repaired. It was handles thru DT by a company that services DT products. I am glad I did even tho it cost more than I was expecting. It was a flat fee regardless of what they did, and after getting them back, I was very pleased with the work. I have some diagnostic skills but couldn't find the problem. It was on a smaller board parallel to the heat sink that I couldn't get to.

To verify prior to shipping they wanted me to check the resistance on the subwoofer and send both the "active and passive amplifier." They wanted the entire crossover section minus the transformer.

If you would like a direct contact to them, just PM me. Don't know if they serve consumers directly, but they did provide a warranty on their work.

 

[DEFTECHY]

Well, THAT sure puts a different paint job on things.
But not surprising to me from DT. Not after I waited 6 months for them to rebuild an amp from a Supercube 1 sub a buddy gave to me, only to find that with a 10" driver and two 10" passive radiators the frequency response dropped like a stone below 30Hz.

Something interesting someone posted about the amp you're dealing with (not that it helps you any): "Basically the power amp is a bridge arrangement powered directly from rectified mains, and is housed on a chassis separate from the backplate with preamp and controls. The only connection with the power amp is thru an optoisolator that carries PWM signal. Seems a lot of effort to avoid the cost of a beefy power transformer."

Good luck with your quest!

Ive talked with Def Tech about repairing this amp, the rep I talked to barely spoke english but said they dont offer repair on this model, might try back again but their customer "service" is rather pathetic these days.

I have read that comment about the amp design before, seems DT bounces back & forth on their amp designs, the later 7002/704/7006 models use an amp with the beefy power transformers but they are all class D with the stupid SMD components, not fun to work on at all. Not sure if the 2000tl with separate amp section is class D, but at least it has mostly normal parts that are easier to work on.. besides the delicate traces on the PCB.

I also own a supercube1 for many years, its actually one of my favorite subs & definitely goes below 30hz without dropping much until the 20's based on freq sweeps Ive done and seen posted. But, DT is well known for exaggerating their specs or more so just using a different measurement to make them look better on paper, they use a +/- 6db or something like that instead of the normal +/- 3bd.... have seen some other companies use a 6 ohm power output spec on amps/receivers too vs the normal 8ohm. But in my experience the supercube1 is a very good sub with a lot more output than many others ive owned or currently own like SVS SB2000.

Thanks for the wished luck!

I just had my Definitive Technology Mythos STS Super Towers sub amps repaired. It was handles thru DT by a company that services DT products. I am glad I did even tho it cost more than I was expecting. It was a flat fee regardless of what they did, and after getting them back, I was very pleased with the work. I have some diagnostic skills but couldn't find the problem. It was on a smaller board parallel to the heat sink that I couldn't get to.

To verify prior to shipping they wanted me to check the resistance on the subwoofer and send both the "active and passive amplifier." They wanted the entire crossover section minus the transformer.

If you would like a direct contact to them, just PM me. Don't know if they serve consumers directly, but they did provide a warranty on their work.

I mentioned above Ive talked to DT, the rep said they dont work on this model anymore but worth asking again. I have since found a company in Il that says they can work on it but didnt sound to sure they could fix the problem even when explaining the visula issues and that I have another working amp, sounds like they just set themselves up to charge people even if they cant fix it, expected a little more reassurance than that. I know of 1 or 2 other private techs that say they can fix it for very reasonable cost with a $50 diagnosis fee that applies to the bill if they fix it. So Im debating on doing that or just trying my luck/skill first.

Thanks for the contact offer, I will PM you for details, I used to have a great contact there, the head of customer service that used to send free amps & parts when needed on some later models I own/owned.. but he & many others are gone after DT was sold to sound united.

 

[DEFTECHY]

@drumbum thanks for the trace repair tip of using telephone wire, that would be perfect for this since its shielded, Ive always used pieces of capacitor leads to repair short runs of traces when they arent close to other solder points.

 

[gadget73]

"Basically the power amp is a bridge arrangement powered directly from rectified mains, and is housed on a chassis separate from the backplate with preamp and controls. The only connection with the power amp is thru an optoisolator that carries PWM signal. Seems a lot of effort to avoid the cost of a beefy power transformer."

sounds like they had the same basic thought I did for getting the voltage swing, but I hadn't really paid attention to the lack of a power transformer. I was assuming a switch mode supply somewhere. Rectified mains directly feeding the amp is certainly a choice. I thought that sort of garbage had largely gone away when the All American 5 radios vanished into history.

at least its got an optoisolator. Better than the capacitors they relied on in the 50s for that sort of thing.


anyway a warning to OP if this is indeed rectified mains, you need an isolation transformer to work on this thing safely.

 

[Boonaroo]

Thanks for the contact offer, I will PM you for details, I used to have a great contact there, the head of customer service that used to send free amps & parts when needed on some later models I own/owned.. but he & many others are gone after DT was sold to sound united.

I have had great results with DTs customer service. My 1st pair of their speakers were BP8s that I found at a thrift. They needed new socks and they sent them to me free of charge. That won me as a customer. I still have the BP8s, The Mythos towers, Super Monitor 350s and a number of ProMonitors.

DT is not my preferred brand, but their built quality, sound quality and styling fits me.