Marantz 2500 Receiver Repair And Restoration

This Marantz 2500 needs some repairs along with restoration both cosmetically and electrically.

A lot of different issues made this unit a challenge to repair but this Marantz 2500 solid state receiver is worth the effort.

The balance control knob of this Marantz 2500 is missing but the shaft is still there. This will make finding a replacement knob easier.  

 I ended up using the balance control knob from a Marantz 2265. This looked fine and the knob fit the shaft correctly. 

The oscilloscopes vertical centering knob has lost it's chrome cover. I'll have to find a solution for that.

From left to right shows what was left of the original oscilloscopes vertical center knob, the knob I used to make a new knob, then the completed knob.

I removed the black plastic from the replacement knob which made the knob more closely match the Marantz 2500 chrome knobs.

As the new knob was slightly larger then the other scope knobs I moved the level knob to the vertical position.

I then installed the newly created knob on the scopes level control shaft. This makes this Marantz 2500 look more complete.

The level knob is just slightly larger then the other two but this Marantz 2500 solid state receiver looks so much better now.

This vintage receiver came with a wood cabinet that is a little beat up but I think it will clean up well.

I have removed the Marantz 2500 chassis from it's wood case. It's time to start checking out this vintage receiver a little closer.

I have removed the top cover from this Marantz 2500. It's always a good idea to take a casual look before powering up vintage equipment.

I have also removed the bottom cover to make sure I wouldn't have any unpleasant surprises after powering up the unit.

The first thing that I see from the top is that the soft start relay is missing it's plastic cover. In addition the relay socket is loose in it's housing.

These covers don't just fall off relays. It appears this Marantz 2500 receiver has been worked on at some point.

There is a lot of dirt inside the relay where the plastic case would normally protect it so it was many years ago when this happened.

There is no case on the relay so there is no identification number. The service manual along with the pin configuration should help me figure it out.

Just to the left of the relay there is a power resistor. Notice the red wire that is stuck to the power resistor.

Power resistors can get very hot. The insulation from the wire melted to the resistor. Were these wires restrained with a tie wrap at one time? 

This is the only Marantz 2500 I've worked on but I don't think the way this wiring is routed it would leave the factory.

It's time to remove the faceplate of this Marantz 2500. I have removed the knobs and there is always plenty to clean.

You will find that any vintage audio restoration and repair will require a lot of time spent with water, rags, cleaners etc. to remove years of grime.

The dirt and grime has even found it's way into the protected radio dial area of this Marantz 2500 solid state receiver. 

I have now removed the faceplate of this Marantz 2500 receiver.

Behind the faceplate of this vintage receiver I found plenty of dirt and dust. Not a surprise after 40 years.

More "Stuff" to clean out from this Marantz 2500's tuning wheel.

The faceplate itself is a mess but it should clean up fine.

It takes some time and some patience but most stains can be removed from faceplates without damaging them.

Cleaning the faceplate will be at the end of this project. I will wrap the faceplate in bubble wrap for now. This way damage to it is less likely.

After powering up this Marantz 2500 receiver I noticed that none of function indicator LED's were functioning.

I measured and there was no 8 volts AC on the indicator board that it requires to work properly.

I found a broken connection that jumpers 8V AC from the dial lamp board to the function indicator via a cable.

During this Marantz repair and restoration I jumped the 8V AC and thought that would fix it. It gave me the 8 volts but it still didn't work.

After troubleshooting I found a shorted diode on the function indicator board.

After replacing the defective diode the indicator LED's were now working in this vintage Marantz 2500 solid state receiver.

Now I'm going to start removing boards in this Marantz 2500 for further repair and restoration. Always take pictures before removing connectors.

Taking pictures allows you get the unit back together correctly. Some connectors are keyed, some are not.  

Serious damage can occur if you install a cable incorrectly. This is not trauma surgery. Take your time!

I have removed the tone amp board for servicing. Having the board out of the chassis makes component replacement easier.

Having the board out of the chassis also makes the cleaning of pots easier. The cleaning of the pots is a must for any vintage restoration or repair.

Taking this Marantz 2500 apart for repair and restoration is not that difficult but keep the screws, washers etc. in a way that makes sense to you.

The push button switches also need to be cleaned. With the board removed you can clean the switches properly.

Any board that has plugin pins I use Deoxit  D100 along with a Q-tip to clean them.

When you have any assembly out of the Marantz 2500 receiver it's a good time to look at the solder points to make sure that everything looks okay.

Once that you have restored or repaired a section of the Marantz 2500 it's a good idea to check your work before moving on.

Usually I wait until the end of a repair or restoration to clean the faceplate. There is no one order that's correct. Do it in the order that's right for you.

I feel the best approach to cleaning this Marantz 2500 faceplate is to use warm water and a little dish soap first.

Get as much of the grime as you can before using a more powerful cleaner. There is less of a chance to damage the faceplate that way.

 I have used Mother's mag polish successfully on many aluminum faceplates but test a small area to make sure you do not have an issue.

You can use soft rags, paper towels, Q-tips, a tooth brush or whatever works for you to get the decades of grime off..

I'll be replacing components on the audio muting board during this Marantz 2500 receiver repair and restoration.

A new Omron speaker relay will be installed.

Almost all of the components needed for this Marantz 2500 repair and restoration are still available or have modern equivalents.

The new speaker relay has been installed as well as new electrolytic capacitors

Nichicon high temperature rated PW series capacitors will be used during this Marantz 2500 receiver repair and restoration.

I'll now replace components on the power supply board. Always take pictures so that you can get everything back together correctly.

You can't take too many pictures. A few extra minutes can save you hours of troubleshooting and/or damage later.

You can mark the cables also. There is no one way that makes sense to everyone. Just do what you need to do to make the project a success.

The power supply is the most important part of the Marantz 2500. If something goes wrong here it may damage the unit beyond repair.

The old regulators lasted 40 years. That's long enough. They are being replaced along with the insulators.

Don't forget to clean up the old thermal compound and add a thin layer of new. 

Now that the new MJE15032 transistors have been installed it's time for the remaining components.

I'll use some modern test equipment to help me with this vintage Marantz 2500 solid state receiver.

I'm using Nichicon PW series high temperature rated capacitors. Notice the 250V-350V rated capacitors for the oscilloscope.

I'm about ready to install the upgraded power supply. This Marantz 2500's power supply is ready to start it's next 40 years.

While the power supply board is out I'll inspect the artwork side for any obvious problems.

I've got the power supply mounted back in the Marantz 2500 receiver. Next I'll hook the cables back up.

During any vintage audio repair or restoration it's best to check your work as you go. After the power supply rebuild the 2500 powered up fine.

I'll now change out components from the tone board and the filter amp board.

The pots are now in a position that makes it easy to get the deoxit in on the tome amp board.

The push button switches are also easy to reach now on the filter amp board.

There are more 40 year old electrolytic capacitors to replace with new Nichicon high temperature PW capacitors here.

This Marantz 2500 repair and restoration will include changing old electrolytic capacitors that have long gone past their life cycles.

This vintage Marantz 2500 solid state receiver requires audio grade capacitors in certain sections.

High grade and high temperature rated Nichicon audio grade capacitors were used for replacement.

I found during this Marantz 2500 repair and restoration that many of the wire wrap connector pins had been touched up in the past by someone.

Where needed, all of the new transistors that were replaced were gain matched.

I have started to remove the phono amp and selector switch board for component replacement.

On the internet you will see people skipping the restoration of this board or tearing the unit down for access. This is not necessary

Tearing the Marantz 2500 apart is not necessary but patience is. You will need to cut many tie wraps and unhook many cables.

Mark the cables in a manner that makes sense to you. You will need to be able to get everything back together correctly.

One of the steps to gain access to the phono board is to loosen the dial lamp board and move it back a few inches into the chassis.

The steps above gave me plenty of access to the phono board for service as seen below. It was a better choice for me then to tear the unit apart.

Marantz could have done a better job with serviceability on the 2500 but it was hand built at the factory so it will come apart.

All of the transistors and electrolytic capacitors will be replaced on the phono board during this Marantz 2500 repair and restoration.

The transistors on the phone board require that they be gain matched. Modern test equipment is a big help in restoring vintage equipment.

New Nichicon PW series and audio grade capacitors have been installed into the phono board as well as new low noise modern transistors.

Probably the most important question when you purchase a restored Marantz 2500 is "Was the phono board restored?" Most are not!

The filter amp board is next. Cleaning this Marantz 2500 receivers push buttons are as important as replacing components.

There was only one electrolytic capacitor that needed to be changed on the filter amp but it was changed. It's 40 years old like the rest of them.

Even the dubbing board had it's pins and jacks cleaned with deoxit during this Marantz 2500 restoration and repair.

The phono section of this Marantz 2500 had a hum when selecting the phono input. 31 Volts from the power supply measured 39 volts.

The issue was caused by two bad transistors on the power supply board of this Marantz 2500 solid state receiver.

After replacing the two defective transistors on the power supply board the proper 31V was now supplied to the Phono board and the hum was gone.

Now the peak indicator and soft start board will be upgraded with new transistors, diodes and capacitors.

Some of the diodes in this Marantz 2500 receiver have a history of failing and should be replaced.

The data that the peak atlas DCA Pro analyzer provides allows me to assemble a modern and reliable equivalent diode.

By combining two modern diodes I am able to make an equivalent component that should operate reliability for many decades.

I have reinstalled the upgraded soft start board into this Marantz 2500. As always give your work a test run before moving on.

Now it's time to move on to the main amp board during this Marantz 2500 repair and restoration.

Once again take pictures before removing any connectors! Write it down on paper! Whatever works for you. It may save you later if you run into trouble.

You can't have too many pictures or too many written notes. Ask me how I know. LOL

I have removed the assembly that contains the power amp boards for both the left and right channels.

This assembly is removed from the Marantz 2500 receiver by removing several screws from the bottom of the chassis.

Between rotted foam along with dirt and grime there will a lot of cleaning to do on this Marantz 2500's fan assembly.

Any vintage audio repair or restoration involves a lot of cleaning. This Marantz 2500 receiver is no exception.

I'll now remove both the left and the right amp boards for component replacement during this Marantz 2500 repair and restoration.

If you remove six screws the main amp board will pull off from three plug in connectors. This makes component replacement much easier.

With the main amp removed I will now replace several transistor, diodes, and capacitors so that this Marantz 2500 can operate as intended.

I have now replaced the 40 year old components on the main amp board. This Marantz 2500 is getting closer to being ready for it's next 40 years.

The Marantz 2500 uses a heatsink tunnel and fan to keep the output transistors cool. I will take the tunnel apart for cleaning.

Whenever you have a fan dirt has a way of collecting everywhere. I'm sure that this section of the Marantz 2500 has not been cleaned in 40 years.

You must unsolder the base and the emitter of the output transistors from the power transistor connection board to remove them.

I use a Hakko 808 desoldering tool that makes this job pretty easy. If you do not have a tool like this it can be a pain to remove the transistors.

Once the transistors are removed the heatsink area needs to be cleaned up and new thermal compound applied.

This Marantz 2500 repair and restoration requires a lot of cleaning but what do you expect after 40 years of service.

Each heatsink is cleaned in the sink with a toothbrush.

The heatsinks cleaned up fine. This Marantz 2500 receiver heatsinks haven't been this clean sense the unit left Japan in 1977.

The back side of the power transistors will be cleaned up and new insulators will be installed.

The Marantz 2500's power transistors are now cleaned up and are ready to start another 40 years of service.

There is grime and old fan foam everywhere including on the power transistor cases.

Cleaning these original Marantz 2500 output transistors will allow them to run cool.

Don't forget to clean the 600's brother the 555.

This Marantz 2500 solid state receiver repair and restoration will include new transistor insulators.

I've cleaned up the heatsink and I'm going to reinstall the power transistors. New insulators and thermal compound also.

The first power transistor has been installed. 15 more to go before this Marantz 2500 receiver can make music again.

The drivers in this vintage Marantz 2500 receiver will be replaced along with  new insulators and thermal paste.

This work takes time so if you take it on don't expect to complete it quickly but it's worth it as it needs to be done after 40 years.

I've completed half of the heatsink tunnel/output transistor work. The left tunnel is complete, the right still needs to be done.

The story on this heatsink tunnel is the same. Remove, clean and replace. This Marantz 2500 repair and restoration is getting closer to the end.

All cleaned up, reinstalled and ready for another 40 years.

I've completed the heatsink tunnel work on this Marantz 2500 receiver and it's time to get everything back together.

The heatsink tunnel is back together and is close to being ready to be installed into the Marantz 2500 chassis.

I have the chassis of the Marantz 2500 receiver cleaned up and I'll reinstall the heatsink tunnel. Then it will be time for some testing.

I'll clean up the fan and get the rotted foam off.

I've cleaned up the fan and I'll now reinstall it into the Marantz 2500 chassis.

The original Marantz 2500 fan was just too noisy even after cleaning it so I will replace it with a new fan.

The rear panel of this Marantz 2500 will tilt down so removing the old fan was not difficult.

I had to make some adjustments of the mounting hardware between the original fan and the replacement fan.

The new fan is much quieter. This Marantz 2500 repair and restoration is one step closer to completion.

This Marantz 2500 receiver powered up fine after reinstalling the heatsink tunnel. Now I will set the bias and DC offset of the amplifier.

 I was able to set the bias and DC offset to factory specifications using the Marantz 2500 service manual. 

One final look to make sure that everything looks good in the chassis before this Marantz 2500 goes to bench testing.

The back of this Marantz 2500 had the grime cleaned up. RCA jacks, speaker, and the antenna connectors were cleaned with Deoxit.

I have installed the faceplate and knobs. I have also done a basic test on the controls before bench testing.

Now it's time to show a little love to the Marantz 2500 receivers wood case. Like the rest of the unit it's a little beat up.

I will not sand the case even if that would make for a newer looking finish. I don't want to take all of the old from this 40 year old wood case.

I used the two wood products shown below during this Marantz 2500 repair and restoration.

The results were very good. This Marantz 2500 solid state receivers wood case is ready to start another 40 years.

 I will use a Sound Technology 3200A audio analyzer for the testing of this Marantz 2500.  

After a vintage repair or restoration the audio equipment should be bench tested. This Marantz 2500 receiver is no exception.

The distortion numbers were very good throughout the various frequencies tested for both the left and right channel.

The channels tracked very near each other throughout the volume control range. Here they are tracking dead even at 104 Watts continuous into 8 ohms.

This Marantz 2500 repair and restoration is complete. It's time for some music!