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Marantz PM-KI Pearl Lite repair

xaviescacs

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This thread is the follow up of a discussion started by myself in a thread about different speaker cables lengths because I wanted to know if that could be the case, in my ignorance. I don't want to keep polluting that thread so I start this one.

The last intervention by @restorer-john, which seems to have some consensus it points to the right diagnosis, is this one. I paste it here:

You have most likely, an oxidised/pitted set of speaker relay contacts. Very, common.

The 'burst' of volume is required to 'cut through' the oxide and then all is well until next time or a period down the track.

Prior to turning it up, one speaker is lower in level and/or distorted.

To confirm it is the relay, take the cover off the amp, turn it on and play at the level where the issue occurs. Tap the speaker relay firmly with a wooden chopstick (safety first) and see if it instantly solves the issue. All you need do is either replace (preferable) the relay or alternately, remove it, pop the cover and clean the contacts with some 2000+ grit wet and dry cut into a thin streamer-like strip, folded over and pulled through the NO contacts.

This is the audio of what happens. It's a 440 Hz tone. As described above, the audio is distorted and unstable before it's solved by turning up the volume. This happens only in the B channel, which I believe I hasn't been used since I bought the amp, 10 years ago. This relay has been waiting for 10 years... Does that make sense? Lack of use can be a triggering factor?

I'm not completely sure about which is the suspicious relay. I've taken some pictures.

marantz_relays_1.jpg


marantz_relays_2.jpg


I think the one (this is a relay, right? :rolleyes:) I'm pointing with the wood is the one that controls the B channel, the lower one, the only that has the problem. Does that make sense? There are another pair of white relays in the main board, but I think they control other things. I'm reluctant to disassemble more pieces so I don't have access to the rear of this vertical PCB where the speaker terminals are attached to be sure the current arrives just at this point to verify this is the correct relay.

I've tried hitting it with the wood (I've hit all the relays nearby in fact :p) but the results are not conclusive. Sometimes, with a hit, the sound changes abruptly, apparently as a result of the hit, but it doesn't get solved.

I can keep trying. I'm on the right track?

Thanks a lot!!
 
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xaviescacs

xaviescacs

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The only measuring tool I have is a simple multimeter. I've checked it's enough to verify the presence of a potential difference between two points.
 
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xaviescacs

xaviescacs

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And yes, there is a missing speaker terminal, which I've ordered because it was broken, but it's on the working channel. I don't think there is any correlation between the two facts, as the issue was purely mechanical on the outer side of the amp.
 

restorer-john

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If the problem only occurs on speakers B, not A, then it is virtually 100% sure the B relay is at fault for the reasons described.

The other thing you can do of course, is swap the missing terminal from speakers B to the speakers A hole and then test. You will then be using the speakers A relay.

Bear in mind, dirty/pitted speaker relays are one of the most common issues with amplifiers. It's possible both relays need cleaning/replacing.

1642284947685.png


This is the schematic of the PCB pictured above:
1642285699803.png


The green and the orange are the left and right 'hots' (+) for each channel. Each channel goes through each relay- A, B and Headphone relay. Plug your headphones in and listen- my bet is it will be fine. The headphone signal is merely the power amplifier outputs dropped via 330R 2W resistors in series. (R751/752)

You can also unplug J709 (pointed out above in your pic) and probe the direct amplifier outputs (with a speaker) with respect to ground. That will bypass the relays.
 
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xaviescacs

xaviescacs

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Thanks for the scheme, that helps a lot, also because the numbers in my board are the same, so I can be sure which components is which. And yes, the one in the right it's the headphone relay, the L753.

The headphones indeed sound fine, it's the first thing I tried, forgot to say that before.

Channel A works because it was working just before the terminal broke, and I've tried combining Channel A Left and Channel B Right and the Left speaker works perfectly and the right was the issue.

I may try to bypass the relays as you suggest, but I think all point out to that relay, as you suggested.

Now, assuming it's the relay, I assume I have to take off the PCB board in order to access the rear part to be able to remove the relays for servicing or replacing, right?

And, looking for the same component, it seems discontinued, or at least there is long wait time, about 3 or 4 months. It's a Fujitsu FTR-F4AK024T. Should I use the exact same component? Or could I look for an alternative with same specs? That time delay also makes me think that perhaps servicing is the best option.

But my major problem is that I'm not sure I have the tools nor the skills to remove the relay if its soldered. I have a toy tin welder, but I doubt it's enough. I see some kits at amazon with precision welder and a sucker for 25 €, perhaps I buy one and try out. I'm watching some youtube videos and it doesn't seem that hard. I've done electronics project in the past but at a very entry amateur level, nothing remotely serious.

Well, I go to bed and I'll think about it while cooking tomorrow.

Thanks a lot.
 
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xaviescacs

xaviescacs

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I've ordered the relays, I'm going to change both. The official channel was too expensive so I've order few of them from AliExpress at very low price. I'll post about again when I start repairing the thing, just for the record.
 
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xaviescacs

xaviescacs

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My relays have arrived. Had to buy 7 of them in AliExpress to get 2 in good conditions, but way cheaper than the official service. I'll see if a have a way to test them standalone and then I'll plan the intervention for the next days. A also bougth a soldering kit for 30 € at amazon. Looks solid though.
 

JayGilb

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Thanks for the scheme, that helps a lot, also because the numbers in my board are the same, so I can be sure which components is which. And yes, the one in the right it's the headphone relay, the L753.

The headphones indeed sound fine, it's the first thing I tried, forgot to say that before.

Channel A works because it was working just before the terminal broke, and I've tried combining Channel A Left and Channel B Right and the Left speaker works perfectly and the right was the issue.

I may try to bypass the relays as you suggest, but I think all point out to that relay, as you suggested.

Now, assuming it's the relay, I assume I have to take off the PCB board in order to access the rear part to be able to remove the relays for servicing or replacing, right?

And, looking for the same component, it seems discontinued, or at least there is long wait time, about 3 or 4 months. It's a Fujitsu FTR-F4AK024T. Should I use the exact same component? Or could I look for an alternative with same specs? That time delay also makes me think that perhaps servicing is the best option.

But my major problem is that I'm not sure I have the tools nor the skills to remove the relay if its soldered. I have a toy tin welder, but I doubt it's enough. I see some kits at amazon with precision welder and a sucker for 25 €, perhaps I buy one and try out. I'm watching some youtube videos and it doesn't seem that hard. I've done electronics project in the past but at a very entry amateur level, nothing remotely serious.

Well, I go to bed and I'll think about it while cooking tomorrow.

Thanks a lot.
Relay contacts will sink a lot of heat. I would make sure the soldering iron is at least 50-60 watts and comes with multiple tips.
You might also look into soldering wick as well as a sucker. Consider it as an investment and you'll have some tools available for future projects.
 
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xaviescacs

xaviescacs

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Relay contacts will sink a lot of heat. I would make sure the soldering iron is at least 50-60 watts and comes with multiple tips.
You might also look into soldering wick as well as a sucker. Consider it as an investment and you'll have some tools available for future projects.
Thanks! I have the sucker as I thought it was indispensable. I'll buy some soldering wick as well.
 
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xaviescacs

xaviescacs

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The original part has been discontinued. The replacement is the FTR-F1AA024T.
Newbie question about relays. The 24 DC V indicates the voltage required to operate? I mean, the voltage it needs to be "closed"? How precise is this? I ask to see if a can test them standalone with some wall power supply.
 

JayGilb

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Newbie question about relays. The 24 DC V indicates the voltage required to operate? I mean, the voltage it needs to be "closed"? How precise is this? I ask to see if a can test them standalone with some wall power supply.
This is the coil specs for the replacement FTR-F1AA024T.
Coil voltage min. 16.8V DC
Coil voltage max. 39.6V AC

A 12vdc wall power supply can put out between 13-17 vdc unloaded and may well be enough to close the contacts.
 
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xaviescacs

xaviescacs

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This is the coil specs for the replacement FTR-F1AA024T.
Coil voltage min. 16.8V DC
Coil voltage max. 39.6V AC

A 12vdc wall power supply can put out between 13-17 vdc unloaded and may well be enough to close the contacts.
It seems the older ones, which are allegedly what I've received from aliexpress, have a wider sensitivity: from 5 to 48 VDC.
 

JayGilb

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It seems the older ones, which are allegedly what I've received from aliexpress, have a wider sensitivity: from 5 to 48 VDC.
I think you misread the data. The 5 to 48vdc range you are seeing is the nominal coil voltage for their 5vdc to 48vdc line of relays.
The "must operate" coil voltage for the 24vdc coils you ordered is 18vdc.
 
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xaviescacs

xaviescacs

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I think you misread the data. The 5 to 48vdc range you are seeing is the nominal coil voltage for their 5vdc to 48vdc line of relays.
The "must operate" coil voltage for the 24vdc coils you ordered is 18vdc.
I see, "Coil Data" table. Thanks.
 
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