I was handed a Genesis P51 V2.2

[Dr Zeus]

Supposedly this amp is very rare, very sought after, and exceptionally good at SQ performance. This is a 6 channel low power amplifier. It has channel 1 through 4, a center channel, and lastly a subwoofer channel. i dont expect this amplifier to be all that rediculous by the looks of the 30A fuse, but none-the-less I am told this amp is hand built in England and is one of the 'best' according to a long-time installer.

This amp accepts power and powers up, only after about ~30 seconds the two long-thin resistors next to the fan get proportionally hotter than I would like. On the PCB it says these resistors should be 100R5W but are measuring 170Ohms. I'm likely going to pull them off and test them on the bench.

 

[Perry Babin]

Was the fan running?

If not, did the fan have 12v on it?

They are large resistors and likely dissipating a lot of heat (when the amp is operating normally).

 

[Dr Zeus]

They are both measuring 175 ohms off the board. I think they are supposed to be 100 ohm resistors.

The fan did not run; but it did move just a tick as soon as the amp was powered. I think thats normal.

 

[Perry Babin]

Did you measure the voltage across the fan terminals to see if it had 12v?

 

[Dr Zeus]

The connector at the board for the fan has 12vDC across it, but as soon as I plug in the fan it drops to .4vDC. Spinning the fan while connected only to the volt meter generates voltage. I think the fan is OK. I hooked the fan up to 12vDC battery and it runs.

 

[Dr Zeus]

[EDIT] Nevermind. My frequency generator must need some cleaning. After rotating the frequency knob back and forth its now sending a clean signal to the amp, which reproduces just about fine.

 

[Dr Zeus]

Should I replace the two 5w Resistors with 100 ohm units? These are measuring 175 ohms, and after they get hot they measure 225+ ohms untill cool.

 

[Perry Babin]

You need to apply 12v to the fan to confirm that it's working. I'm assuming that this is a 12v fan.

If you can clearly read the 100R5W, they are out of tolerance and probably should be replaced.

 

[Dr Zeus]

The fan works on a 12v battery. The resistors say nothing on themselves, but on the board its clear they are 100R5W. Can I use square wire-wound resistors in place of these?

 

[Perry Babin]

Sometimes revisions are made and the boards have already been printed. This means that the silkscreen may not be accurate.

It's possible that overheating could make them drift and since they're essentially identical, they may change in value in a similar way but it's unlikely that they would both be the same value.

I think I'd leave them as they are.

 

[Dr Zeus]

The top one in the photo hit 320 degrees F after about 5 minutes of playing time. I unfortunately do not have the top cover to this amplifier. i wonder if these resistors are supposed to be heat sync'd.

If nothing else, I think this amplifier is fine as it plays clean on all channels.

 

[Perry Babin]

I don't think their location near the fan is an accident. I think the fan is supposed to keep them cool.

If one is getting much hotter than the other, there may be a problem. If both are at the same temperature, it may be normal.

This type of resistor (from what I can tell from the photo) appears to be made to handle high temperatures. Some resistors can withstand 500°+ continuously. Although 320°is hot, it may not mean that the resistor is in danger of failing.

 

[TheBaronGroog]

Did you get this sorted? Gordon Taylor is on diyma if you ever need any advice on his amps.