Light bulb limiter

[DjKrish]

Hey friends,

I would like to build a light bulb limiter circuit to test my amplifier to prevent the newly fitted components burning if there's still a fault in the amp section. The amp is 300watts rated. So can i use 100watts bulb as how everyone uses or i need bulbs watts higher than 300 for example 400 watts bulbs cause my place there's only 100watts bulbs. If i need higher than 300watts, how do i align them? Parallel or series?

4 bulbs (400watts) in parallel/series?

Inputs will be highly appreciated.

[joshnz]

Re: Light bulb limiter

the bulbs will be parallel to each other.
Also it may power on with 100 watts depends on the design.
Id suggest starting with a 100watt and seeing what happens.

[DjKrish]

Re: Light bulb limiter

the bulbs will be parallel to each other.
Also it may power on with 100 watts depends on the design.
Id suggest starting with a 100watt and seeing what happens.

Thanks a lot for the swift reply The power amp is a InterM PAM-360. So 100watts should be enough? I have attached the documents for your reference.

[SteveNielsen]

Re: Light bulb limiter

The worst thing I can imagine is it will trip the current protection relay. Try one and see. If it does trip the relay than add another 100w bulb in series. I think putting it in parallel will halve the load impedance, increase the current and trip the relay again.

[budm]

Re: Light bulb limiter

100W is what I use for working on the amp also, the main key is that to find out if the unit has shorted circuit or not, the lamp should come up bright then dim down as the main caps charged up, I do not use the lamp for full audio output test, just for finding out if the outputs or the power supply are shorted out or not. I have bypass switch so I can bypass the lamps, I use two lamp sockets for one of my version.
http://s807.photobucket.com/user/bud...tml?sort=3&o=0

http://s807.photobucket.com/user/bud...tml?sort=3&o=1

[DjKrish]

Re: Light bulb limiter

I tried 100watts bulb, its kinda dim when turned on. Only the transformer, power board and main board hooked, amp board is disconnected. Does this mean the transformer and power board is working fine? Or the bulb is not enough wattage?

[budm]

Re: Light bulb limiter

That is good, it is bad when lamp stays on at full brightness.

[DjKrish]

Re: Light bulb limiter

That is good, it is bad when lamp stays on at full brightness.

Ok with the amp board plugged in, the bulb is still dim, but the protection light is still on All the components on the amp pcb thats faulty has been replaced, its good as new now.

[budm]

Re: Light bulb limiter

That means the protection circuit still detects large DC offset at the output stages, so you still have more torubleshooting to do.

[DjKrish]

Re: Light bulb limiter

That means the protection circuit still detects large DC offset at the output stages, so you still have more troubleshooting to do.

Ive noticed there's 2 variable resistors on the amp circuit. Is there any adjustments need to be made? Or shall just leave it like that as how it is originally? As per the dc offset, ive checked the speaker output terminal with multimeter, it shows zero reading. Please check pictures.

[budm]

Re: Light bulb limiter

So the speaker relay RL301 still not turned on?

[DjKrish]

Re: Light bulb limiter

So the speaker relay RL301 still not turned on?

Yes still not turning on with the red protection light on. Is there anywhere else i should be checking? Please bare with me as im not a pro in repairing but i know how to do stuffs like checking components with meter, checking voltages, soldering and checking schematic diagram and replacing components. Not really a pro in in-depth repairing, that's why i turned here for help. Almost all the main parts in the amp pcb has been replaced. Still no go, luckily im still running the unit with the bulb limiter to prevent those components from burning again.

[budm]

Re: Light bulb limiter

The diagram is really poor, it does not show what is driving the PROT LED (connector AN14 pin 7), on the LED display board.

[DjKrish]

Re: Light bulb limiter

Yes i know Thats the only diagram i can find on the net. I called interm, they said same model there's a few version of schematics and service manuals. Really kinda stuck now. Really need help on this. I just dont know where else to check anymore. Any possibility on the transformer causing this? Or the power filter caps on the power board? I took out those 2 big caps and tested using ESR, its low esr and uf almost closer to rated value.

[momaka]

Re: Light bulb limiter

Check the voltage on the two main caps (the 2 big ones) and report what it is. Should be equal on both. Also check those white wire-wound resistors and see if any has or have gone open circuit. Better yet, check their resistance and compare to their printed values. Do this with the power off and amp unplugged, of course. Let us know what you find.

And to confirm what others said about the 100W light bulb - yes, it should work (as you saw). I myself have tested a Behringer EPQ-1200 that way. As long as the volume is kept down so that the speaker output is under 1W, it should work. Above that (and depending on the amp design itself), it may trip the protection due to low voltage. One trick I like to do is to measure the voltage across the mains voltage after the light bulb. If it falls below 90V, the device you are testing may fail to work normally due to too low of an input voltage. Again, it all depends on the device's design.

[lookimback]

Re: Light bulb limiter

I'm trying this and the lamp isn't lighting. I soldered the wires from the lamp to a blown fuse to make it easier. So I have a 100 watt bulb in series, replacing the fuse. I'm getting stby, and the voltage across the pfc cap is 150v off, 160v on. Do I need a lower wattage bulb?

[lookimback]

Re: Light bulb limiter

I think I figured it out. I tried a 75w bulb and it lit, real dim, very briefly. I see also that it only lights if the PFC isn't charged.