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HK Projector HF Limit light on constantly


TheSoundGuy43

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Hi Guys

 

This is the first time I've ever posted to a forum and I joined specifically to see if any of you sound genius' could help me work out what's wrong with my speaker. I have a HK Projector active Mid/Top that has the HF limiter light on constantly. I am up for trying to fix it myself but I was hoping someone here could help me diagnose what may have gone wrong and where I might get the parts to fix it. Im pretty clued up with all things sound but have never gone inside one of these speakers. Any help or advice would be greatly appreciated. Thanks.

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Presumably the other top works OK?

 

What colour does the HF limit light show? (Green = signal present, yellow = soft limit, red = full limit - from the manual) I'm guessing red?

 

This info just might help someone make more sense of what could be any number of failure options.

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I have fired up the whole system and this speaker seemed very tinny and missing Mids more than anything.

As you mentioned an HF limiter light I assumed your problem was with the top end, possibly caused by high-frequencies "nasties" getting in from the power-supply, the amp or your source. If the problem is missing Mids it could be a faulty driver, but that wouldn't explain the light (unless the driver has gone short-circuit).

Edited by sandall
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Hi Alec. Yeah all the other mid/tops and subs work perfectly. The light is on constant red, as soon as it is powered, even when there is no signal being sent to the speaker. I was wondering if it was the driver that was faulty but I was just trying to isolate the problem before I go spending money on something that doesn't fix it. Its a pretty old system and from what I gather has been all over the world and worked pretty hard. Judging by some of the other gear I bought from the same guy it could well have been been pushed too hard, he seemed like the kind of guy that had all the gear and no idea. Do you know if there is a way of manually deactivating the HF limiter or is it just something that kicks in automatically?
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Hi Alec. Yeah all the other mid/tops and subs work perfectly. The light is on constant red, as soon as it is powered, even when there is no signal being sent to the speaker. I was wondering if it was the driver that was faulty but I was just trying to isolate the problem before I go spending money on something that doesn't fix it. Its a pretty old system and from what I gather has been all over the world and worked pretty hard. Judging by some of the other gear I bought from the same guy it could well have been been pushed too hard, he seemed like the kind of guy that had all the gear and no idea. Do you know if there is a way of manually deactivating the HF limiter or is it just something that kicks in automatically?

I'm no technician.

I would, however, check that the two drivers in the cabinet are functional - if you're competent to do that, I'd suggest you do.

After that, I'd be seeking the services of someone more capable than me - the indicator light could be a symptom of any number of root cause faults.

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Thanks Alec. Im starting to air more to the driver side of things. I have checked the user manual for the correct part details and it says the original driver is as follows.

 

 

B&C DE85 8OHM 2" DRIVER

 

Link here

 

And I've seen them on another site for half the price:

 

Link here

 

 

Can anyone help me confirm that these are the same parts before I waste my money?

 

Cheers Guys!

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Before you spend that sort of money you really need to check the drivers out.

 

Do you have a multimeter? If not, go and buy one.

All of this!

 

The other simple check I'd be doing is to disconnect both speakers and pass a low level signal through them. That should tell you very quickly if there's a problem with each. If you're looking at driver replacements, you should be capable of doing this?

 

And definitely, don't go replacing drivers until/unless you've identified that you have a failed driver. For goodness sake, you never know, your problem could be as simple as a connector that's become loose (unlikely, but could be).

Edited by Alec
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I took your advice and ran a signal through the speaker and it seemed to be missing the mid frequencies and was really tinny. I opened the speaker up to see if there was anything obviously wrong and I immediately found that a fuse on one of the PCB boards had blown. Im guessing this is the PCB for the mid range speaker and would explain the tinny sound. Ive ordered some 4 amp slow blow fuses that should arrive in the next couple of days and If that's all the problem is then im a very happy man. Just wanted to say thank you for pointing me in certain directions and ill let you know if this solves the problem. Cheers Guys!
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Sometimes the fuse blows due to "volume up to 11" moments, sometimes it blows when something else has also failed. It would be fortunate if a fuse blew before any semiconductor it was/maybe protecting.

 

It's very fortunate if the first check reveals the only fault. If the repair really is just changing the fuse then change it for the proper one, (FF to T matters).

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When you fit a new fuse disconnect the speaker BEFORE you turn the amplifier back on.

 

Turn it on and see what happens. If the fuse stays OK then I'd be inclined to put a multimeter, set to DC volts, across where the speaker would be connected. You should only see a very small DC voltage if anything. Anything over 0.5V would indicate a knackered amplifier.

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  • 2 weeks later...

Hey Guys

 

Ive taken things a few steps further as per your advice. Firstly I changed the fuse that had blown which fixed the continuous red light on the HF limiter however it hasn't fixed the problem. When I put a signal through the speaker all I get is the HF coming from the horn but absolutely no MF at all. I then took your advice and tested the Driver resistance with a multimeter which was coming in at around 6.8 ohms and from what I've read this indicates that the driver is not the problem.I moved on to testing the the PCB for the MF and when I connected the probes of the multimeter I got some fluctuating numbers that were all over the place. I also noticed that a previous owner had drawn silver crosses on two of what look like heatsinks. Im starting to think that the problem was already identified and I was sold a duff speaker. My bad, I took my eye off the ball there but im still dedicated to fixing it. Has anyone ever changed one of these pcb's? Theres a large ribbon cable soldered to it so it doesn't look like an easy job. Any advice or tips before I go pulling things apart?

 

Thanks

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First thing you need to do is identify which amp module is which. Each driver is driven by its own amp module and these operate in bridge mode. That is each one of those modules has two amps on it, one amp driving one end of the speaker and the other amp driving the other end. At opposite ends of each module are the speaker connections (on right angled Fast-On spades). By tracing the speaker wires you will be able to identify which module is which.

 

EDIT:- I just might be wrong about this. If there is only one module then the speakers are driven in normal single ended mode. Let us know whether there is a single or pair of modules as the advice will change.

 

The modules are almost completely independent of each other and it sounds as though your HF amp is functioning fine but the MF amp is dead. Concentrate on that one.

 

On each module there are two fuses, one for the + supply and one for the - supply. Check continuity of these but if either of them is blown DON'T replace them yet. Next disconnect both wires to the MF driver and if possible pass a signal through the driver to check that it really is OK. You can use any old small amplifier for this but if you haven't got one then briefly connect a small 9V battery across the wires and listen for a thud from the driver.

 

If you did find a blown fuse then there is likely to be a shorted output transistor or two in one of the amplifiers on this board. This is easy to check - with the meter on continuity, put one probe on the nut which secures the heat sink and the other probe on the speaker connection at that end of the board. Repeat for the other transistor and then check the transistors at the other end of the board in the same way (using the other speaker connection). If you haven't seen any readings below a few kilohms then the transistors are probably OK.

 

NOW you can replace the fuse! By the way, T4A is the correct one as identified on the PCB.

 

Next power up the amp with the speaker still disconnected and with no input connection and with the gain control turned right down. With your meter on DC volts check across the spade terminals at each end of the amp. You should see less than 0.5V as Brian said above. Actually on these amps it is likely to be a lot less than 0.5V. Then check with the meter on AC volts and again there should be just about zero volts between the spade terminals. Now check between signal ground and the outputs. Again there should be less than 0.5V on either D.C. or A.C.

 

Feed a signal in and turn the gain up and you should see the signal present (green) LED come on.

 

Report back and we can all enjoy the next instalment!

 

Dave

Edited by DrV
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