Marantz 170DC static noise (both channels)

[paul_peraic]

Hello

I have a Marantz 170DC that has a static crackly noise in both channels (this is not effected when the gain is increased or if I have RCA input )I have replaced all electrolytic capacitors and re-soldered a few suspect joints but I still get this noise could anyone please help ?

[Mooly]

Not familiar with the amp (do you have a circuit ?) but other than dry joints I would perhaps suspect something like a transistor common to both channels... regulator maybe, or a component in a regulator.

Any that run normally hot might be favorites.

Can you alter the fault by tapping the PCB etc. Does it only appear when hot ?

[paul_peraic]

Hello

Here is the service manual

Marantz Model 170DC | Owners Manual, Service Manual, Schematics, Free Download | HiFi Engine

[paul_peraic]

Sorry forgot to mention the noise is there when either hot or cold

[sakis]

there is absolutelly no chance that inside this machines exists even one propely working electrolytic ....

the spscific model uses dual costum made capacitors that fail l get leacky or all shorts of corosion down under ...

now even if the big caps are still working up to some point there is going to be a million other small problems like bad soldering, and small electrolytics in the protection area, amplifier boards, secondary psu, and vu meter board

this is an amplifier worth fixing and really deserves to be fixed ...

yet again this is not an easy job to do it is time consuming but at least it will not cost a fortune ...

if you can follow procedure ....here is some instruction vintage amplifier repair/upgrade manual

[Mooly]

Hi Paul,
I've had a really good look at the circuit and can't really see anything that's common... apart from the obvious of course.

Be absolutely sure that with RCA inputs disconnected and the gain turned down that the noise is present on both channels... I know you said it was... 100% sure yes
Make sure you have just the amp and speakers connected.

If so that only really leaves the PSU as a common item.
Don't discount the obvious... is the mains plug/fuse/wires OK... not loose. Same for the internal fuse in the amp. Also the mains switch. Voltage selector intermitent ?

Does it respond to physical movement ? Tapping the PCB etc.

[sakis]

oppps ....for some reason it seems that i missed the point that said all electrolytics are replaced

ok then that is very good ....the paricular amplifier features a small plastic conector for the input RCA if you for any reason replaced those are the new onew isolated froma the box ???

then gain did you add or remove or replacced any grounds ??? cause this may as well be ground loop

regards sakis

[paul_peraic]

Originally Posted by Mooly

Hi Paul,
I've had a really good look at the circuit and can't really see anything that's common... apart from the obvious of course.

Be absolutely sure that with RCA inputs disconnected and the gain turned down that the noise is present on both channels... I know you said it was... 100% sure yes
Make sure you have just the amp and speakers connected.

If so that only really leaves the PSU as a common item.
Don't discount the obvious... is the mains plug/fuse/wires OK... not loose. Same for the internal fuse in the amp. Also the mains switch. Voltage selector intermitent ?

Does it respond to physical movement ? Tapping the PCB etc.

Hello Mooly

I have put in shorting plugs in the RCA inputs and it is now coming from the right channel only .

[Mooly]

This could be hard to fix quickly.

Is the noise very loud ?

If you measure the DC voltage at the speaker output (the offset voltage) does it seem to alter randomly a little ?

Is the offset normal, ie zero volts. Might be worth giving the offset adjust pot a good turn and seeing if it's gone "noisy". Reset it afterward for zero DC volts at the output.

Does it respond at all to "tapping" the PCB ?

If it's a component, then favourites would be any small disc ceramic type caps or old "suflex" caps (like polystyrene ones). It's unlikely to be a small resistor etc.
It could be a semiconductor, but that wouldn't be a first choice though for this fault perhaps. Semiconductors if faulty often respond to freezer spray... don't blast the parts, just "drip" a little on to the device. Should have no effect on a good part.

See how you get on with that for starters... good luck

[paul_peraic]

Hello Mooly

The noise is not very loud it is a quiet CB radio static type sound audible from the listening position it is there even when the volume gain is down and there is no input .

Yes the DC will not stay at zero and does alter randomly a little especially in the right channel , and it does seem to respond to tapping of the PCB tough I am not 100% on this .

I have tried adjusting the DC through the adjuster pots but as you mentioned the DC alters randomly I have also cleaned it with contact cleaner .

Thanks Mooly