20 Most Recent Yamaha P4500 Power Amplifier 2-Channel Questions & Answers

Sign up here, you should be able to download the service manual. http://www.hifiengine.com/manual_library/yamaha/a-s700.shtml

Hi...
It could be on a thermostat inside. I would check the connections to the fan.It might have it's own fuse.
If you have a meter ,you can check for DC volts to the fan and continuity on the thermostat (if it has one)
2 leads mounted on the heatsink ..usually black and round with slide-on terminals

Hi Joel, although we've sourced detailed schematic for this P4500 amplifier, there are no many voltage details on it for manufactures sake. Anyway, mine findings are. Secondary winding on main transformer should supply no less than 2 x 75 volts which makes after rectifying and filtration no less than 2 x 90 volts on capacitors with amplifier without input signal. Also transformer has to be very "hard" , otherwise amp will start clipping before reaching stated wattage on output.

here is a link to guide you:Where do I Find a Service Manual?

The manual says the heat sink is too hot or an unacceptable DC voltage was sensed going out.http://www.retrevo.com/support/Yamaha-P4500-Amps-manual/id/962bh144/t/2/Generally speaking, an amp attempts to protect itself from heat, shorts, overloads and operator exuberance by refusing to turn on or stay on; or it may turn on but produce no audio to the speakers. Overloads can be from excessive periods of high output or marginally low impedance loading by the speakers; and shorts would be wiring issues or a speaker blowing up. You should be able to feel if it's hot. WHY is it overheating? Make sure it has sufficient ventilation on all sides and that vent holes are not blocked by dust balls. Ensure the fan (if equipped) is running as designed (some only operate on demand). Clean dust and debris from it. If the amp comes back on after cooling, you're lucky. They only have so many self-protection cycles in their lives so continuously resetting or cycling their power without addressing the cause can do more harm than good. If it protects immediately on a cool power up you should disconnect the speaker connections and try it 'nekkid'. If it comes up then diagnose which lead(s) are shorted. If it does not come up the problem is internal and should be left to an experienced and competent hands-on tech. Check for loose speaker connections at the speaker as another possible root cause for intermittent shutdown.

'Splitting' leads is never the best way to distribute a signal. The best solution is to use the parallel inputs of the Yamahas to chain them together: mixer to amp1, amp1 to amp2, amp 2 to the Cloud. You should only need to use one input on the Cloud to drive all the channels, using the input switches at the rear.

Let me know if you need any clarification on this.

This is a service manual of your device and it can be downloaded for free and I hope it is suitable for you (included schematic diagram). Go to this web site:

http://elektrotanya.com/yamaha_p4500.pdf/download.html

When you use the link you get to a page where you have to wait some minutes to be possible the downloading so please be patient.
Good luck!
Thanks.
gylacz

Generally speaking, an amp attempts to protect itself from heat, shorts, overloads and operator exuberance by refusing to turn on or stay on.

Overloads can be from excessive periods of high output or marginally low impedance loading by the speakers; and shorts would be wiring issues or a speaker blowing up.

You should be able to feel if it's hot. WHY is it overheating? Make sure it has sufficient ventilation on all sides and that vent holes are not blocked by dust balls. Ensure the fan (if equipped) is running as designed (some only operate on demand). Clean dust and debris from it.

If the amp comes back on after cooling, you're lucky. They only have so many self-protection cycles in their lives so continuously resetting or cycling their power without addressing the cause can do more harm than good.

If it protects immediately on a cool power up you should disconnect the speaker connections and try it 'naked'. If it comes up then diagnose which lead(s) are shorted. If it does not come up the problem is internal and should be left to an experienced and competent hands-on tech.

Check here and here

Suspect an overload in the power section, or more likely the main amp. A semi-conductor device is now acting like it was a piece of wire. Easy to spot with an ohm meter, it will just like you have touch the test probes together! My guess it will be one or more of the things on the big heatsink that's gone.

There is a bad soldering joint somewhere. Take the top off and follow the speaker connections from where the left speaker connects. Keep an eye out. If you can get the bottom off, look at the PC board solder joints. If in doubt resolder them.