Marantz SR320 Amp Repair

[derek92994]

A childhood friend of mine wants this amp fixed. Many good times and parties with this amp (not to mention the amount of drugs we did), has been in his family since the early 80's. I'd like to see it working as much as he does, got him by for many years. Symptoms were a loud buzz through the speakers then an electrical burning smell. I'm suspecting caps and have made a list of the ones around the power supply and large heatsink. Can hunt most of these caps down at the local electronics store but the 6800uf ones will have to be bought online (expensive). Looking for advice on where to start. Cheers

 

[NavLinear]

Damn D2. I think the THC residue heated up and that's why it copped a buzz - the smoke your bud smelled was the reignited oil.

 

[derek92994]

Wouldn't surprise me

 

[NavLinear]

Wouldn't surprise me

Do you have a service manual? I'm looking at the moment.

 

[NavLinear]

Are the speakers ok that were hooked up to the receiver? If the amp passed dc that could be a bad thing.

 

[derek92994]

Are the speakers ok that were hooked up to the receiver? If the amp passed dc that could be a bad thing.

Yeah speakers are fine. The amp was repaired for a humming sound many years ago, looks like it came back but much worse.

 

[derek92994]

Do you have a service manual? I'm looking at the moment.

No service manual yet.

 

[NavLinear]

You'll want to protect the STK4833 as I suspect that is difficult to replace. So far the data sheets I've found for that are written in Japanese. The schematic and other electronic drawings/tables are in Engrish. I wonder if this is a Japanese only design.

 

[derek92994]

See how things go with the cap replacement. I'm all ears for any other advice.

 

[NavLinear]

Do you know if it is a low frequency hum? If so you can start in the power supply section and go from there. I just found the Semiconductor STK4833 for sale at a great price - not sure where it comes from though.

http://www.electronix.com/shopping_cart.php

 

[derek92994]

Not sure, I can't get it to power up now. Wasn't there when it made the hum. I don't think it was a very low frequency, more like a buzz.

 

[NavLinear]

Damn - I can't find the service manual or users manual for this guy. Since you're in Oz maybe you can ask the Wizard.

 

[derek92994]

I have rarely used service manuals, but I have looked for one. The only service manuals I have used are for mechanical (like cassette decks). I usually go blind and caps are more often than not the problem.

 

[NavLinear]

Electrolytic capacitors are one of the suspect components in older electronics. Let us know how it goes - have fun with this one.

 

[derek92994]

Electrolytic capacitors are one of the suspect components in older electronics. Let us know how it goes - have fun with this one.

I need to wait for my pay later this week to see if I can afford to order the 6800uf caps online, the others should be quite affordable.

 

[laatsch55]

Without a service manual or schematic you can do more harm.than good. Like you I would get the power supply working and the next thing would be to measure DC offset at the speaker terminals and go from there. Most STK module amps I've seen are put together pretty much the same so even if you don't find the service manual for this one another component using that same module may be a big help.

 

[derek92994]

Without a service manual or schematic you can do more harm.than good. Like you I would get the power supply working and the next thing would be to measure DC offset at the speaker terminals and go from there. Most STK module amps I've seen are put together pretty much the same so even if you don't find the service manual for this one another component using that same module may be a big help.

Does that mean start replacing caps or do you want me to measure voltages from the power supply as is?

Gotta get ready for work, will be in touch.

 

[laatsch55]

Get the power supply working then check the output...