Hi there.

I'm a long-time electronics technician, but my experience is of radio, radar, data transmission, image processing, IT and automotive systems.

I've been handed a Warrior IS1000 amp to fix, but someone's been in it before me.

On the power supply PCB there are four fuse-holders, none of which have fuses in, and there are no markings to indicate the correct values.

The owner reckons all four were 20mm 8-amp quick-blow type, but while that might be correct for the input fuses, it seems unlikely for the output pair, which I think would be a higher current rating.

Can anyone tell me what values these fuses should be?

Even better, does anyone have any technical information or a schematic of this unit, or can you tell me where to get such information?

Thanks for your interest.

GadgetDC

Warrior amps are distributed by Prolight Concepts http://prolight.co.uk/contact-us. They may be able to help.

Thanks for the contact info.

I've had a reply from Prolight Concepts confirming fuse values at 8A.

Excellent!

They don't have a schematic so if anyone knows where I can get one I'd still appreciate the info.

I have one somewhere a warrior audio impact IS1000 i will take the lid off it and see what it says on the fuses tomorrow..lets hope they didnt change the spec during preduction

ok i took the lid off in MY is1000 they are all F8A250V fuses the uses are marked on the board as FU103 FU104 FU203 and FU204..as i say these are the fuses in my is1000 but if they changed spec at some point these falues may not be correct.

Thanks for checking.

All the info I have confirms the fuses are meant to be 8A, 250V, so I think I can put this issue to bed.

Now to figure out why when channel 1 has a high resistance that doesn't blow the supply, channel 2 only presents 1.2 Ohms to the incoming HT without any signs of burning or short circuit...

Very techincal oh very technical!
This is why I have a technically minded roady!

Can you explain what you are actually measuring!
A high resistance shouldn't blow the supply, depending on the circuit it may well have OC protection though.
On channel 2 when you say it only presents 1.2 ohm, are you saying the speakers measure 1.2 ohm? Don't forget that the figure quoted for speakers isn't the DC resistance, but the AC nominal impedance.

Jim

Hi Jim
Nothing external is connected.

I expect channel 1 with the high resistance is fine, but the low resistance of channel 2 would cause the 8-amp HT supply fuses to blow instantly and cannot be right.

Each channel output stage appears to be a bank of 5 push-pull pairs of complementary PNP/NPN transistors in parallel. The +/- HT supplies go via low resistance high power resistors to the top and bottom of the complementary pairs.

With the PSU disconnected I connected a multimeter on an ohms scale across the HT supply connectors to the output stages of channel 2 and got a reading of 1.2 ohms, and roughly half that to earth. When I switched the multimeter to diode test mode it read 0V so there is no semiconductor junction detected.

From this I reckon there's a dead short across the output stage of channel 2, but whether it's a transistor or ten that have given up, or something in parallel with them, I don't yet know. Like I said earlier, there is nothing connected to the speaker outputs.

I have found a small broken track on the back of the PCB in the channel 2 area, not big enough to carry much current, and wonder if this was the original problem and has caused the output stage to self-destruct.

Gadget

I agree and would put money on it being one (or more) of the transistors that has gone.
Without having a schematic or actually knowing the circuit, what I would do is compare the junctions of the transistors with the ones on the other channel, before you start though, either discharge or unsolder the large capacitors (unsolder preferably). Once you come across a suspect, disconnect it, also disconnect the equivalent one on the other channel and then continue to compare the rest of the transistors.

Jim

You really have to measure the transistors out of circuit, or at least lift the legs of any resistors on the output stage. From memory in some amplifiers there are often very low ohm resistors connected to the output stage in some manner, which often will throw up confusing readings with a DMM.

I'd check the rectifier diodes / Bridge first if they are downstream of the fuses, failing that its highly likely to be output stage or even a dodgy reservoir capacitor

After much head-scratching:

There was a solder bridge across one of the channel 2 temperature sensors, meaning the channel 2 fan never switched on.

A pair of channel 2 output transistors and their driver had died and gone total short circuit.

I'll change all 10 channel 2 output transistors anyway for reliability, in case the overheating has weakened the other ones.

There's also a couple of bulgy capacitors on the amp board so they'll be changed as well.

Many thanks to all for your help.

Gadget

More importantly than that, it would upset the bias to the output stage.