Marantz 2500 Refurb

[rBuckner]

My neighbor just around the corner, and a good friend, told me he had a Marantz with a scope in it down in his workshop. Turns out it was a 2500! I finally have time to start refurbing it for him. Here it is:

I brought it up slowly via my DBT and using a variac to bring up the AC slowly. All seemed well and I got the "click" of the relay. After going diect (no DBT), it came up okay and draws about 0.75Amp AC, about right for a beast at idle. A quick check of the speaker terminals revealed DC noffsets of 5 and 10 mV so I connected speakers and after some fiddling with controls got some sound. It's in dire need of DeOxit for sure!

Next I played with the scope's front panel controls until I got a display. It was very dim and later I found the rear panel brightness pot and cranked it up all the way, as will be seen in the last photo below. It seems the "audio" mode display is a bit overblown and the front panel Level control doesn't do much - again likely dirty... well I hope so!

So The scope of the job is a cleaning, total recap, convert dial to LED along with the dial pointer and all adjustments. I also have to locate a pushbutton cap, a regular knob and deal with the broken off balance control. The one bummer is the damage on the upper edge of the raised bezel. I have had some sucess before repairing these so will give it a shot.

This will be my first 2500 so come along and learn with me while I go!

 

[bktheking]

Love the vintage knob lol. Ill be watching.

 

[rBuckner]

Yeah, it imparts a tube like sound to the output!

 

[Jailtime]

Tons of pictures, please! I've always wanted to see how these things come apart. I looked inside a 2385 once, didn't look like all that much fun.

 

[jblmar]

Should be a fun project.
I'm sure you know to be careful working around the CRT circuits.

 

[rBuckner]

Yes, pictures galore! Any tricky / necessary breakdown actions will be noted. Don't wait for a part list though, I tally them up for costing but don't track them specifically to the reference designator.

Yeah, thanks for the warning jblmar, I used to work on color TV's and also on XY tubes in a waveform anaylzer back in the 80's. I've been bit by 10kV which hurts more than a little bit!

 

[mr.jones]

Wow...that should a real beauty when it is done !

rBuckner is a Marantz wizzard and a heck of a nice guy too...:thmbsp:

I have a 2245 that Randy did a complete rerurb on.

Picked it up DOA on Craigslist. Randy worked his magic on it and it and boy does it sound good.

 

[rBuckner]

Didn't get too much done last night, just covers off and an initial look-see.

Top cover off

Right side. Note the lower left corner, it looks like the rear panel can hinge down. There's nothing in the SM about that.

Left side

Bottom view

Front left view with knobs pulled off

Front right view with knobs pulled off

I store knobs in plastic ice cube trays as it keeps them safe and in the order they were on the front panel.

With the two brass nuts removed, the faceplate was pulled off. One of the LEDs was sticking and I noticed that they all looked like they had been glued on.

Turns out there are two wiring bundles that are connectorized and can be undone. Now we know!

The scope bezel was removed. One screw is longer than the other but it doesn't seem there's a reason why. I know someone has been in this unit, perhaps they switched a screw from somewhere else.

Front "nudie" view

 

[SchweinHaus]

Wait. Are you just refurbishing that for a neighbor... for fun? What a neighbor.

 

[rBuckner]

Not quite. There's a fee and he's paying for parts too. I'll be selling it for him too.

 

[Allegroconbrio]

Not quite. There's a fee and he's paying for parts too. I'll be selling it for him too.

Nothing beats having some fun and making some money at the same time. Will be following your restoration closely Best of luck!

Rich W

 

[rBuckner]

I wanted to remove the scope tube for the chassis cleaning so here goes. First I removed a bracket at the rear of the tube which keeps the socket from falling off the tube.

Then there's a bracket just behind the rubber gasket at the faceplate end, held on by 3 screws. It's not in the picture below but as can be seen the tube is out after just a little gentle prying.

Here's the tube socket, thankfully there's missing pins so as to ensure it can only go on correctly.

The chassis was then blown out with compressed air and then washed. It was dried out with compressed air after that. It wasn't that dirty but is even nicer all cleaned up. There will be more hand cleaning as the work goes on, for sure the transformer top will get more attention!

 

[pete_mac]

Nice! I have a 2500 in the queue which is awaiting a service and possible resto, so I shall be watching this thread closely.

 

[rBuckner]

Pardon the slow pace! I did work on it Sunday afternoon and here's the update. I didn't have those higher voltage caps "in stock" for the power supply board so have stuff on order.

The power supply board comes out by unplugging the 5 wiring connectors and removing the 3 screws at the top edge. Nice feature!

Here's the "hole" the power supply came out of.

Caps to be replaced are marked red so none are missed.

While the p/s board was out the two rectifier diode bridges were pulledup, cleaned, and got some fresh thermal transfer compound.

Another thing I do to not forget anything is to use a checkoff list of work items to be performed. I developed it for Marantz 22xx receivers but it can be used with anything.

End view of the power supply board with three power transistor pass elements.

Cleaned up and silicone insulators installed. No need for thermal compound with these.

Loosening the transistor screws caused one to pop loose from it's pc board pads. The years of heat undid the adhesive so it came loose very easily. First the traces were scraped clean for soldering.

Bus wire is crimped onto the pin and laid on the trace.

Solder makes the connection.

All done!

I put in the caps I did have on hand. That bad boy relay is 10A rated for speaker protection use. Not cheap.

I'll be back in a few days after parts arrive. In the meantime there's cleaning to do.

 

[Baron K Rool]

This is the best type of thread.

Would you mind sharing that to do list with AK? It looks quite useful!

 

[Allegroconbrio]

Loosening the transistor screws caused one to pop loose from it's pc board pads. The years of heat undid the adhesive so it came loose very easily. First the traces were scraped clean for soldering.

Bus wire is crimped onto the pin and laid on the trace.

QUOTE]

Nice bridge work on those lifted pads.

 

[rBuckner]

Baron: Sure! It's an Excel sheet IIRC. I could try doing a PDF then attaching them. If anyone wants it as the Excel file PM me an e-mail address and I'll send it along. Keep in mind it was developed specifically for Marantz 22xx models.

Allegro: Many thanks for your compliment!

 

[rBuckner]

Alrighty then, more fun.

Power supply is done. Cleaned the flux off the back, just don't like it on a board with several hundred volts.

There's a small board on top of the amp assembly which has a relay. Replaced the on electrolytic cap and found that I had the relay. The old one is on the left and the new on the right. The new one has more pins but the end ones are not used so they just get clipped off.

The new relay's pins are larger so had to drill out the pc board using a #36 drill. Of course a pad cracked off!

Here we go again with the bus wire.

All soldered up.

When reinstalling the board, put the wires into the wire guide on top first.

Then put the board in and pop the wires back into the clip on the chassis.

The scope board wiring unplugs and after two screws pulls right off a connector on the edge of the scope switching board which is mounted on the back of the faceplate. There was only one screw in this unit holding the scope board in but a spare was sourced.

There are no electrolytic caps on this board but I spotted some 1/2 watt resistors with a bit of a "tan" from years of heat. All but one measured OK, the off one was about 10% high and is the lowest one in the picture. New parts were put in all positions anyway.

After all that was done I realized when looking at the old relay that it was rated 48V and I put a 24V one in! So out it came and you guessed it, I didn't have one so now two are on the way so I have a spare. So not much progress worth reporting is going to happen until early/mid week. Have a safe and blessed long weekend all!

 

[bktheking]

48v relays are difficult to source in general.

 

[Overundr1]

2nd the comment on 48vdc relays. Have several stored away as they do seem to come and go from the usual supply houses. Waiting for the tunnel disassembly
Thanks for sharing btw.