I have a SUB-TS2 from Harman Kardon. The sub emits very low level sound when receiver sub configuration setting is +10db and the sub volume level is set to max. The speaker cone and surround are in good condition and the electrical resistance is about 3 ohms across the coil so I don't think it is a physical problem with the speaker itself. I suspect something in the circuitry leading up to the speaker. The fuse and transformer inside the unit are good - so the board is getting power. The DC voltages at a several points on the board also seem to be correct (per HK's diagrams). None of the components on the board are visibly damaged. I have tried connecting the sub to another sound source and tried different cables with the same problem. Can you provide any suggestions on troubleshooting the board components (assuming my hunch that the problem has to do with the board components)? I do have the schematics from HK that I can provide. Thanks in advance.
Thanks for responding to my post so quickly! I am getting some sound when I connect through the sub input and the speaker level inputs. It is just very low sound output. I have to be up next to the sub to hear it. The pot measures 1.8 ohms at min setting to 30k ohms at max setting. When I measure the voltage from my amp, I get a fluctuating signal between .1 and .001. When I measure the voltage from the terminals going to the speaker itself, the range isn't much different. FYI, I am using a digital multimeter for these tests. Any other suggestions?
I don't know what happened to this post from last night but I'll try it again.
There is a website you can access which provides technical support for many brands, HK included. It always comes up on my browser/search engine whenever I do a search for any brand specific item. If you can't find it, let me know and I'll repost the address. It is a small fee based service though.
I can find no information on this sub. Is it a sub that came with a rack or mini-system?
If it is new, it is under warranty. Send it in for repair.
If it is out of warranty, there is no point in repairing a plate amp. Replace the entire unit and move on to listening to music.
Have you read the owner's manual's "Troubleshooting" section?
I tried sending in a steady sub signal from an mp3 that I downloaded from the web. I am measuring .064vac from the amp, .2vac at the sweep of the pot at max volume, and .042vac at the speaker terminals. Looks to me like something between the pot and the speaker terminals.
Need to know the voltage applied to the pot to determine if the sweep is putting out over 50% of input at max. What is the capacitence labelled on the pot? Beyond replacing the pt if output is low, partsexpress sells new plate amps for cheap...
What are you trying to find? The chances of a potentiometer failing completely are extremely - and I mean extreeeemely - rare compared to any other component in a plate amp. If the pot made noise, clean it or replace it. That doesn't seem to be the case here.
I have no idea if the op knows how to take proper measurements but doesn't, "I am measuring .064vac from the amp", say anything to you? If that's a correct measurement - which I'm not at all certain it is since the op has never mentioned how he's driving a signal through this system, just that he's getting these measurements - that's way less than one tenth of a volt output. I would expect a powered subwoofer to play at low volume with about 1/20 V "max" coming into it. Wouldn't you?
Then there's this, ".2vac at the sweep of the pot at max volume". Amps can certainly be configured in different ways but normally you wouldn't expect a gain stage in front of the pot. Without an intial gain stage in front of the pot there would be no gain obtained from the pot itself. At full rotation a potentiometer is essentially out of the line and the voltage coming into the pot should in most cases be the same as the voltage measured at the pot's "+" output terminal. IOW what is being presented to the input of the potentiometer is the full output of the driving amplifier (in this case 0.064 volts as measured and reported) and the pot can only reduce that voltage. If there are no gain stages in front of the pot, then the output voltage of the amplifier (0.064 volts) should be the voltage at the output of the pot at full rotation. It is not. So what's going on here?
Tell me what you're trying to determine by knowing the value stamped on the pot and maybe I can comment but, as is, I don't see your point for wanting to know. It doesn't seem germaine to the dicussion.
"Just play a source that should have a subsignal and turn off the main speakers to save yur ears."
"What is the voltage being applied to the pot within the sub amp and what is the voltage coming out of the pot sweep?"
You're going to have to make up your mind whether you want him to "just play a source" or to have a fixed reference voltage. If you go for a fixed voltage, you'll need to know what that voltage is - 0.064volts won't do.
"The pot measures 1.8 ohms at min setting to 30k ohms at max setting"
A 30,000 Ohm pot? Could be I guess but that would be unusual.
"When I measure the voltage from my amp, I get a fluctuating signal between .1 and .001."
"I am measuring .064vac from the amp"
Well, I suppose that first range would be correct if you weren't using a fixed level in. Still, less than 0.10 volts out from the source is suspicious if the op is feeding a voltage from an amplifier. The amp needs to see at least 1 full Volt in and probably more like 2 Volts.
"I tried sending in a steady sub signal from an mp3 that I downloaded from the web."
Fine, but we still don't know what voltage is supposed to be coming from the MP3 signal. What's feeding this signal to the sub? A MP3 player or is it being fed through the amplifier? Until we have a fixed reference Voltage that meets the plate amp's needs, none of these measurements mean very much. If the amp can only output one tenth of a Volt, then we have other problems. However, the op stated he had run the sub with another amplifier and had the same problem. That makes me very suspicious of what's being done here.
".2vac at the sweep of the pot at max volume, and .042vac at the speaker terminals."
According to this there is actually less voltage at the speaker outs than at the plate amp in? That would make the amplifier one large resistor?
Did I mention you don't generally repair plate amps?
All - thanks for the info. Jan, I am playing an mp3 (85Hz_sinewave.mp3) from my cd player that is running through my Sony amp. The subwoofer (sub input) is connected to the Sony amp via the RCA sub connector on the back of the amp. I'm playing the mp3 at a constant volume sufficient to hear the sound from my front speakers. When i measure the voltage coming from the amp going into the sub, it measures .064 vac. On the other side of the pot (which is also the output of an operational amplifier), i meaure .2vac at max volume (on the sub). I'm using a digital multimeter to measure the voltages on the board. Should i be using another method to measure accurately? Can you recommend another testing procedure to isolate the problem component on the board(s)? I'm interested in attempting to fix the subwoofer because IMHO this is a good subwoofer and seems to be ok except for a board component that costs a few pennies. The trick is (obviously) determining the faulty component. Thanks again for all your help.
Do you know how to read a schematic well enough to track signal flow through the various circuits of the plate amp and with sufficient skills to troubleshoot your amplifier without replacing lots of parts that cost pennies which were not defective? Do you have a schematic for this amplifier?
Do you have any other diagnostic tools other than a DVOM? A scope or a signal generator? A load resistor?
Do you understand why using 85Hz as a test signal for a sub might not be your best choice? Do you know why 0.064 Volts out from your amplifier is suspicious? Do you have the facility not to play a MP3 input loud enough for you to hear it through your front speakers but to remove your amplifier and speakers from the set up and to directly drive the subwoofer amp to full power while monitoring its Voltage and current draw? How the amp draws its power and how much of either component is being consumed will generally tell you where to begin your troubleshooting.
Do you have access to buying small lot parts should you need to replace an ic? Do you understand "equivalent" parts should that ic not be available? Do you know how to read resistor color codes to establish the correct value for a burned component?
Do you have a soldering station and the necessary skills and tools to actually perform a repair on a 32 pin ic? Do you know how to safely handle ic's? Do you know how to identify, say, pin 1 on an ic?
Do you know how to read a schematic well enough to track signal flow through the various circuits of the plate amp and with sufficient skills to troubleshoot your amplifier without replacing lots of parts that cost pennies which were not defective? Do you have a schematic for this amplifier? I do know how to read a schematic and have one for this sub. i can make it available to you. Let me know.
Do you have any other diagnostic tools other than a DVOM? A scope or a signal generator? A load resistor? I do not have these - only have a DVOM.
Do you understand why using 85Hz as a test signal for a sub might not be your best choice? Do you know why 0.064 Volts out from your amplifier is suspicious? Do you have the facility not to play a MP3 input loud enough for you to hear it through your front speakers but to remove your amplifier and speakers from the set up and to directly drive the subwoofer amp to full power while monitoring its Voltage and current draw? How the amp draws its power and how much of either component is being consumed will generally tell you where to begin your troubleshooting. Without a signal generator, i'm assuming i'd have to drive the sub with my existing Sony amp - are you saying i need to increase the volume on my Sony amp so the voltage hitting the sub is higher? I can do this if needed. What voltage level at the sub is sufficient for testing?
Do you have access to buying small lot parts should you need to replace an ic? Do you understand "equivalent" parts should that ic not be available? Do you know how to read resistor color codes to establish the correct value for a burned component? I can obtain the board components needed and can read resistor codes.
Do you have a soldering station and the necessary skills and tools to actually perform a repair on a 32 pin ic? Do you know how to safely handle ic's? Do you know how to identify, say, pin 1 on an ic? I do have the skills and tools necessary to replace component parts.
Then other than not being able to monitor voltage and current draw and test individual components, I see no reason why you shouldn't have been able to track down the problem by now.
85Hz is above where most subwoofers would have their maximum output. You should be working with a lower frequency signal on the order of about 40Hz with the crossovers bypasssed. It would be very nice to see what the signal is doing at that point by monitoring it on an oscilloscope. Is the waveform distorted or clipped or non existent? Does the amplifier draw excessive current as voltage is applied and level is raised? That would tell you where to look and most likely where not to look for problems. Any of those things should get you into the right area of the amp to track down a failed component. Without the oscilloscope, there's no way to tell what's happening and you are wasting your time.
The manufacturer should tell you how much voltage is required for proper testing. Normally a plate amp will require between 1-2 volts input before it will be driven to full power. But you'll need more than 0.064 volts to do adequate troubleshooting. Driving the amplifier from a receiver is less than desirable. A load resistor would also be nice for testing purposes. Knowing to begin with that 0.064 volts is not adequate for testing would have been nice.
".2vac at the sweep of the pot at max volume, and .042vac at the speaker terminals."
Realizing what you were measuring was not normal would have been a first clue to realizing you were measuring wrong.
A DVOM is not adequate for anything more than basic troubleshooting. The only thing you can do with the meter is to go along the circuit and test for proper voltages. If you find something that is suspect, then you can remove the component and do simple measurements for function. Beyond AC and DC voltages most DVOM's are going to limit you to testing for continuity and resistance which means you can test resistors out of circuit and not much else. Replace the component and then check for voltage again. That's about as insightful as looking at the components and the board for burn marks and far more time consuming.
You can replace suspect components one by one and test for proper function but you're likely to end up with a $500 plate amp using that approach. You need to know whether a component is functional due to its own failure or whether a component is out of spec due to a problem soemwhere else.
Supplying me a schematic is not going to change this situation. I'm not capable of tracking down the problem over a forum. I'm not familiar with the amplifier and I'm not interested in devoting my time to telling you piece by piece and part by part what should be happening when you don't have the proper monitoring equipment to tell me what is actually happening in the amplifier or whether an ic or transistor is nonfunctional when measured out of circuit.
This is why technicians charge their fees. Yes, most replacement components cost far less than the labor involved in the repair. But the tech and the shop have invested in the right test equipment to do troubleshooting and in the training on how to use and interpret the equipment. Thinking you can get the amp running for a few pennies when you don't have those facilities is extremely wishful thinking - particularly when you don't even have the facilities to test an ic which should be abundant in most plate amps. Even without an ic in the amplifier, you don't have any way to test a capacitor or a transistor for operation. If the power supply checks out for proper voltage, where do you go from there? I can't tell you because you can't tell me what is happening with the rest of the amplifier.
"Looks to me like something between the pot and the speaker terminals."
"Between the pot and the speaker terminals is the entire amplifier."
And that diagnosis is about the extent of what you can trace with your DVOM.
On top of this, you've been told plate amps don't normally get repaired, they get replaced.
Here's my advice once again; call the tech hotline I mentioned earlier. Spend the money required to have someone assist you who has the proper test gear whether that is on line or in a shop. You do not have the facilites to troubleshoot this amplifier.
Now, there may be others on other forums who have more experience with plate amps than I do - I suggest replacing anything that cheap. However, with only a DVOM at your disposal you're telling me you think you could carve Mount Rushmore with a butter knife if only I would tell you how.
Bottom line, either pay someone with the proper facilities to test and possibly repair the amp or buy another.
Audio projects or just projects? I have a 90+ year old house worth of projects, I can't finish one without finding another five that need attention. The weather last year stopped me from painting outside and finishing the repairs on the fence so those are the priorities this year. Workers are installing new cabinets in the kitchen and that will be the next inside project for me until weather permits outside work. I'll be stripping and refinishing woodwork for the next few weeks. The hifi always sounds better after a few hours of killing off braincells with stripper and inhaling lead paint fumes warmed to bubbling with a heat gun.
I don't require a schematic for any of that.
Audio projects are under control. 50 year old tube amplifiers can always be cleaned and treated with some sort of conditioner on the contacts but that won't happen until the kitchen is done. I really don't at this time have any audio projects sitting undone that would seriously impact the sound quality of the system. And I'm happy with my cables 'cause I'm just not going to spend any more money on cables. Part of that is the system just hasn't changed that much in recent years so there's nothing to tweak or to try or to trade. Filing CD's takes the most time right now.
So, other than general housekeeping I'd say I don't really have any audio projects going.
My DishNetwork receiver went on the fritz last week so I'll have a replacement to install - if that counts. That should keep me busy for at least an afternoon.
