Help! Marantz SR-8500 that is clicking

[sjdemark]

Hi,
I have a Marantz SR8500 receiver that seems to be stuck in protection but I cannot figure out why. I'm hoping that there is a tech or someone who has experienced this that can point me in the right direction to fix it. I have repaired several receivers and many power amps, so I generally know my way around audio equipment, but this one has me stumped. I also have the service manual and have studied it for days...

The symptoms: When powered on, the receiver just clicks on and off, about every second or so. There is no display when the receiver is clicking. The clicking is coming from the relay on the standby board. The interesting thing is that if I push the multi-room button, the clicking will stop and the display will light up and allow changes to the multi-room setup. Also, in no case am I able to get the receiver to go into service mode.

The measurements: I measured all of the voltages coming out of the power supply board and they look correct. I also measured the test points for amp failure, heat, and power line failure which go back to the CPU and they all read 4.9v which I think is good. All of the output transistors measured good, and the reciever does not draw much current (approx 50 watts) when on. It looks like the CPU is bringing the unit into standby because the standby lead alternates between 0 and 4.9v as measured at the power supply and alternates at the same time as the clicking.

So basically, I'm running out of ideas for where to look. Any help would be greatly appreciated.

[sjdemark]

Anyone??? I'm hoping someone has run across this problem in the past...

[mhinke]

I can take a look if you sent me the service manual,

Maybe there is an impedance sense?

Good luck, Mike

[Enzo]

Find the output bus for each channel. Not the line running to the speaker connections, but the actual output side of the powr amp - inboard of the relay. I don't know that unit, but it either has discrete transistor outputs or a power amp module. usually there is a coil of wire inductor in series with the output. Usually it is inboard of the relay, though not always. Probe that is a voltmeter and see if there is any DC offset.

If it has a power module, look up the pinout and see if its output pin has DC on it. If it has discrete transistors, a good common point to pink up what the output is doing is one of those fractional ohm power resistors used as ballasts. Typically half an ohm or less.

If there is DC sitting on any of the outputs, the protect circuit will time out, come on long enough to detect the DC then cycle off agin. Obviously there are many other possibilities. But in my limited experience, that is th most common reason for protect.

Outputs can go to DC without any of the transistors being shorted. A little open resistor somewhere can do it easily.

[sakis]

the specific amplifier has a very powerfull cpu with a sophisticated software ....beyond others has a sevice manual and service mode function with wonderfull diagnostics tolls

keep in mind that this a 15MB manual with 192 pdf pages and will requier quiet a lot of reading to start communicating with

you are welcome to have it so please email me

kind regards sakis

[ghg]

Well, have the service manual, too.
Any idea where to get the software for firmware update/verification ?

BR

Gary

[sjdemark]

Thanks for the suggestions everyone. This was a VERY difficult unit to troubleshoot with this failure mode, but I think I got it. Long story short, the problem was a bad solder connection on a logic gate chip on the CPU board. I stumbled on the problem by using a spray IC cooler on the various ICs. When I sprayed that logic gate chip, the receiver fired right up. All has been well ever since I reflowed the solder connections.

After doing a search on the web, I've seen that others with the Marantz SR8500 have had the same problem. Hopefully this info will help someone...