Seeking advice on fixing an old amplifier which is working but not entirely.

[David_]

Hello.

Me and my friend is trying to fix his old amplifier(which has a great sentimental value) which is acting up, but I have no experience with these sort of things and was thinking that I would try and see if any of you might know what the symptoms might stem from. This post may become a little longer than most posts but I'll try and describe the situation as well as I can.

It's an Marantz Model 1515 AM/FM Stereo receiver, I will try to the best of my abilities to describe what is wrong.

The controls are working but from time to time the audio of one of the speakers cuts out, my friend says he has at times fixed it by giving the amp a smack with his hand... No need to point out the positive effects of slapping you amp around

He has also at times fixed it by switching from mono to stereo and the speaker is more often cut out in stereo mode than it does in mono mode, also he has some times fixed it my fiddling with the volume control.

He is playing music through he's PC with a AUX cable and he has noticed that the speaker cut's out less frequently while he has the PC volume setting at max, and the speaker cut out may also be fixed by pulling the AUX cable out and re-inserting it on the PC end of things.

That's about it.

Since this amp has such a great sentimental value I/we have thought to replace any component which seems to be tired or nearing the end of its life.
It's and old amp, he got it from his father who bought it with he's very first salary ever and he is now around 55 years old so an estimate would be that it is about 30-40 year old. My friend has frequently used it since he was 12 years old(he is now 27 years old).

So we are interested in any "standard" or known service procedures, from the experience I have of disembowelling old amps we are not going to find any replacements for the potentiometers at a reasonable price(just assuming) which I guess is why some of you would have tipped us about those sprays that hare used to lubricate potentiometers. We are going to get one of those since we want to restore the state of the amp as much as we can(while not spending any huge amount of money, a max amount is set some where around 116,53USD(1000SEK) or 120USD).

I have thought to de-solder the big power supply caps and examine them with my LCR-meter, would you agree that that might be of any use?

That's about it regarding how far I have thought about it, right after I have posted this post we will open it up and take a look(we have done so previously but I don't remember much from it) and we appreciate any tip or suggestions on what we can do to preserve the condition of the amp as well as what to do to fix the speaker cut out.

When I hear "speaker cut out randomly" I first think about checking the electric connections going from the speaker to the place of origin inside the amp(I no very little about amps so I don't know right away where the audio signal is coming from) but the details of how the cut out is resolved by my friend makes me think that it doesn't sound as a simple loose cable/connection.

That's pretty much it.

Regards

 

[biff44]

it might be as simple as a cold solder joint. Back in the day, they used rosin flux with the solder, and that rosin got trapped inside of the solder joints. Eventually the flux can travel and cause microcracks and beome insulative. You can just take a hot soldering iron and CAREFULLY reflow each solder joint. You might need to add a little new solder to some of the connec tions.

google cold solder joint, they have a gray appearance instead of a shinny metallic appearance. And they will bubble a lot as you heat them up....the bubbling is a good thing, just don't breath in the smoke.

the 2nd most likely problem is the electrolytic capacitors were made out of paper and an fluid insulator. they dry out over the decades, and stop being capacitors. You can buy a "capacitance tester", which looks like a small voltmeter, and test each one, and replace the bad ones with modern capacitors.

this all assumes the tubes are good!

 

[Audioguru]

The receiver is 30-40 years old. Don't you think its useful life is finished? You probably will not find replacement switches and pots for it. Then replace all its electrolytic capacitors.

Kiss it goodbye and bury it.

 

[BradtheRad]

My sister had practically the same Marantz unit. Beautiful silver and gold tones. It too developed a problem with one channel cutting out. The headphones always worked okay.

I decided the problem must be in the headphone jack. The contact to the speaker was old, tarnished, dirty, etc.... causing an intermittent. That was the most likely thing that accounted for the symptoms.

A cleaning was called for, except the contacts were not easy to get at. I think I remember spraying electrical contact cleaner into the hole where you plug in headphones. (Perhaps I removed the cover of the receiver, to look for dripping cleaner.) Anyway I tried to use enough of the stuff. Then I inserted and removed the headphone plug a few times, in hopes that would help to clean the tiny area where the contacts touched.

I think it worked, for a while.

 

[c_mitra]

I call these symptoms a design feature.

Seriously, most of the old units were made much better (compared to the standards of the yesteryears) and a thorough cleaning is needed. Check all solder joints (advice #2), clean all contacts (don't ask me how) and debug in small steps. Is your headphone outputs are coming fine? That will tell that most of the stuff upto that point are fine. If a good slap works most of the time, it is very likely a bulky component and a weak solder. The motherboard also will have some signatures- some areas darker than the rest, some resistors look aged and things like that. You have listed several issues but the cause may be only one or two.

The speaker contacts: they have the press type cable connectors, just cut off 1/2 in of the speaker cable, strip a bit, tin it and reinsert again.

You always find the fault in the last place you look at. So it is wise to start looking from the last place.

 

[Audioguru]

I have an HH Scott receiver that is 52 years old and a Yamaha receiver that is about 25 years old. They both have intermittent problems caused by silver contacts on switches and the silver has corroded (tarnished). I have always used gold plated contacts in all my audio designs with never any problem. The cleaned switches work fine for a few months after using contact cleaner spray then many switch movements but fail again over and over. The HH Scott receiver recently had its main power supply filter capacitor suddenly fail open-circuit. I tried to "steal" the main filter capacitor from the Yamaha but it is permanently glued in and cannot be removed.

 

[E-design]

You can download the service manual for this on the web free. Looking briefly at the manual, I see fused outputs on the audio output channels. The fuse or fuse holders can be intermittent after this many years, and a good clean may be all that is needed. Some switch cleaning spray into the jacks can also help. A good look over with a magnifying glass may spot some suspect/cracked solder joints.

 

[David_]

Okey.
We have planned to take it apart and clean everything, one thought though.
While looking for cold solder joints, I have previously on smaller devices simply reheated every solder joint adding just a little of new flux core solder in order to be sure I don't miss anything.
When you have old solder joints like that and reheat them the solder behaves rather badly and it never ever looks good but adding just a little new solder use to restore the behaviour and result in a nice looking solder joint.

Could that be a bad idea do you think?
If I am prepared to reheat and add a little solder to each joint why wouldn't I do that... I can't think of any reason.

 

[c_mitra]

Okey.
We have planned to take it apart and clean everything, one thought though.
While looking for cold solder joints, I have previously on smaller devices simply reheated every solder joint adding just a little of new flux core solder in order to be sure I don't miss anything.
When you have old solder joints like that and reheat them the solder behaves rather badly and it never ever looks good but adding just a little new solder use to restore the behaviour and result in a nice looking solder joint.

Could that be a bad idea do you think?
If I am prepared to reheat and add a little solder to each joint why wouldn't I do that... I can't think of any reason.

I guess it is fine- in fact it is a good idea. In fact, I think a little bit of flux is essential so that the solder melts quickly.

 

[Hawk44]

I cut my teeth repairing things like this. Don't know what all the unit has one it but I would gently clean any switches it may have, if possible and the headphone jack would need it also. If the jack is wired so as to cut the speaker out when a headphone is plugged in.... Could tell you more if I could see the schematic. Let us know what you find. The soldering is a good direction to go in, but I wouldn't forget the jack and any switches.

 

[David_]

I haven't even looked for a schematic yet, but let's see what result it gives doing what has been said so far.
That is a thorough cleaning, "re-solder" all joints, clean all contacts/switches/jacks, and lubricate the potentiometers.

 

[c_mitra]

I haven't even looked for a schematic yet, but let's see what result it gives doing what has been said so far.
That is a thorough cleaning, "re-solder" all joints, clean all contacts/switches/jacks, and lubricate the potentiometers.

And that is all - there is nothing more than that.

 

[schmitt trigger]

Something else.....
I assume this is a transistorized unit, correct?

In those days, power transistors were TO3 packages. These devices were usually fitted into TO3 transistor sockets.

These sockets will develop intermittent contacts.

Make sure you check and clean those too.