Marantz 140 Amp - bad VU meters and ???

[02County]

I recently acquired a Marantz 140 amp which I am very excited about. The seller gave me a good deal on it with some other items of equipment but said the amp had problems - namely it develops a hum after it gets warmed up. That said, he hadn't played it in years.

I've just played it for an hour with no noticeable buzz - seems to work great. The only issue I've found is the VU meters don't appear to work.

Is that a simple enough fix and are there any other things I should be doing to get the most out of this amp? Thanks AK - Jake

Oh and dumb question - does this thing have a power switch? Or does one simply leave it "on" all the time?

 

[Lavane]

Its meant to be plugged into a "switched" outlet on the back of a preamplifier. Turn the preamp on and the amp comes on. Is there a switched outlet on the back of whatever the amp is connected to? If the amp has been stored away for some time, try giving the meters a little tap.

 

[02County]

Thanks, Lavane. Yeah, I'm learning about preamps now - a childhood of receivers-only has not prepared me for this moment but it's pretty awesome anyway. I picked up the amp with two kenwood receivers, one of which (KR5600) I'm going to try to use as a preamp/tuner running through the 140.

My plan on the VU meter was to let the thing warm up and then play something at moderate loudness, maybe give the needles a bit of a tap, and see if I can get them bouncing again. Other than that, based on what I've found, the options are either very expensive or just learning to live with dead needles.

 

[Lavane]

Hopefully someone chimes in about the meters. I remember a post telling how to possibly fixing them but couldn't find it.

 

[bktheking]

First thing is to put an ohm meter on the + and - of the meter terminals to confirm they aren't stuck- if you meter doesn't have the juice try the diode function. If they do move- try cleaning the connectors going to the meter driver board and confirm you have a good ground going to the boards.

 

[wlhd1610]

I have a 140 in the shop right now.
The resistance across the meter disconnected is 1.9 k ohms.
Interestingly enough the needle deflects over to -2db as I tested it with my dvm.
There is a section in the service manual that describes how to calibrate the meters.


Bob

 

[WillVT]

I've been running a 140 for a few years now. I find with mine that the meters barely move unless I really crank it. I'm not sure if this has to do with the output level of my preamp or what.
On another note, it's really easy to put LED replacement lamps in this thing. I found them on ebay for just a few bucks. It really brings it to life visually.

 

[Lavane]

The meters not moving or very little unless you crank it up a bit is normal. If I remember, I had to use a scope to adjust the meter boards.

 

[02County]

I was wondering about that and am now feeling a little sheepish - okay, I guess I shouldn't jump to the conclusion that the VU meters don't work when I've only tested the amp on fairly efficient speakers (4-ohm norman labs) at low volumes (i.e. 5:30 am when the kids are still asleep). Stand down, everyone. My apologies. I'll run some hendrix through the amp later tonight, when everyone is awake and partying, and we'll see if I can get the needles to move.

 

[02County]

yeah, I was totally out of it on that one. Meters work fine. Apologies again. Thanks Lavane for bearing with me.

 

[catrafter]

IIRC, the meters aren't actually measuring power, just voltage. You don't have to have speakers or a load connected to see if they work.

If you calibrate them as per the service manual all you need is a 1kHz signal source connected to the input and a voltmeter capable of AC RMS measurement connected across the speaker terminals, no speaker or dummy load required.

Tom

 

[Lavane]

Ya, the meters on these are mostly for show. Nice little amps though. Easy to work on too.

 

[organiclawn]

Ya, the meters on these are mostly for show. Nice little amps though. Easy to work on too.

Aren't they all for show.... Just picked one up off craigslist today... same issue not loud enough... but for real the left is below the negative 20 to start out... can you tweak it to start out at 0

 

[Lavane]

Aren't they all for show.... Just picked one up off craigslist today... same issue not loud enough... but for real the left is below the negative 20 to start out... can you tweak it to start out at 0

I didn't play with the adjustments other than to adjust them per the manual. I guess you could adjust one to read more at lower volumes, if that's the issue, but something isn't right. Is the volume the same in both speakers with the level controls set the same? That would be a different issue from the meters.
Look at the meter trimmers. They should be set around the same for both.
Maybe someone messed with one or both of the trimmers? I had two of these amplifiers and still have one. I had an issue with one of them where one channel's output was lower than the other. I found a leaky cap on one of the amp boards. It would make buzzing noises also intermittently. A dirty gain control pot can cause volume drop also. These really are easy amplifiers to work on. They are very modular. Remove a few screws and the amp boards just unplug. When I recapped them I think I only had to unsolder one wire other than when I replaced the main caps.

 

[thxdave]

I have one (started a thread on it) that had a buzzing transformer. I stuffed more cardstock into the gap between the core laminations and the outer copper band that surrounds the xformer and that seemed to tame it. Haven't been able to get back to finishing the rebuild with too many other projects getting in the way but I'm anxious to get it fired up. BTW, what is the wattage output of the 140....70 per channel?

 

[FOH Engineer]

Tread lightly on the meters. I did a deep dive to find someone that can actualy work on them and in general, it's a lost art.

 

[Lavane]

I have one (started a thread on it) that had a buzzing transformer. I stuffed more cardstock into the gap between the core laminations and the outer copper band that surrounds the xformer and that seemed to tame it. Haven't been able to get back to finishing the rebuild with too many other projects getting in the way but I'm anxious to get it fired up. BTW, what is the wattage output of the 140....70 per channel?

With fresh caps you can get 90+ wpc out of these. I got 93wpc out of one of the two I had. The other was over 90wpc also I just don't remember exactly. They are factory rated conservatively at 70wpc. I've done the same thing with transformers myself along with using rubber washers under mounting tabs of the transformer.

 

[thxdave]

I tried the rubber washers first but it did nothing to quiet the xformer. So, I took it apart and was going to have it re-dipped by a local company that rebuilds electric motors in case the laminations were coming loose. Before I went that far, I added the extra cardstock into the outer casing and it seemed to work.