Marantz 2500 Refurb

[rBuckner]

Outside of a fruitless balance slider search, I got the parts order in and swapped out the old film caps for the new polypropylene ones in the tone control and filter boards.

Cleaned the caked on flux off the back of the boards too. Several rounds of picking, alcohol scrubbing with a toothbrush and compressed air. All pots and switches got a little DeOxit sprayed back in them to be sure they're going to work well.

 

[rBuckner]

TA7316 replacement / upgrade

I'm also considering modding the tone control board to replace the archaic TA7136P op-amps. I layed out a small pc board to take a modern SMD SO-8 package having the OPA604 or LME49870 in mind although other single op-amp chips would probably work. I also put pads on for a "nuissance" cap should it be needed. That's the small value one that goes from the output back to the non-inverting input to stop oscillation.

It would use a right angle IDC connector with .025" square pins so possibly the original holes for the TA7136 SIP package may be too small and have to be drilled out. The connector could be omitted if so and bus wire or resistor leads could be used. I'll be hoping for a prototype pc board order to be needed at work so I can sneak the little bugger in! Stay tuned for updates.

 

[rBuckner]

I have been messing with what to do to fix the broken off end of the balance control. Here's the story in pictures.

The balance control as it was.

I was contemplating what to do when my eyes alighted upon a Sansui 9090 sub chassis that I had bought to harvest the driver board. There were some toggle switches with the correct tab on them! Here I have drilled out the Marantz control's arm. I actually drilled the Sansui's arm out first then one hole of the Marantz control first, then bolted it together in order to have the secon hole align when drilled.

The control has to be mounted lower so I used a round file to enlarge the holes in the front chassis plate to the lower side as the add-on tab was to go on the top side of the arm. It looks close but it doesn't scrape.

The add-on tab is now screwed in place with 2-56 hardware.

I did a test fit of the front panel and found that the white plastic piece on the back side was too thick and hit the screws so I took it out.

Here's the white piece. I've done a test notching and have since sanded the back side flat. I have yet to test fit it but will edit this post once I do.

 

[rBuckner]

Here's a long overdue update. It's time to dig into the output amp assembly! I figured that the rear panel hinges down for a reason so I took that approach to disassembly. First I tookout the four black screws holding the fan and grille to the back panel, then removed the 6 screws holding the chassis rear panel to the inner chassis and hinged it down. Poing! I popped off a small bit of glued on sponge with a slot in it to hold an orange wire coming from the AM antenna so I recommend taking the wire out first. It will go right back on with a dab of RTV silicone.

Here's the start of the hinging down, the orange wire is already popped off as can be seen to the right of the power transformer.

This is about as far as it goes.

Here's something that's a bummer, the fan's power wiring is done at the bottom and there's no way to unsolder it given the limited access. Wires were cut and will be spliced when reassembled.

There are 10 screws to be removed from the bottom and wiring plugs that were diagrammed then unplugged and voila, out she came!

As Halloween is coming I thought I'd post a scary shot!

The gaping void where the amp module was. Got some cleanup to do here.

This is the end view with all of the heatsink fingers sticking up on the inside of the "tunnel". The tunnel itself is two "U" shaped aluminum extrusions that have a tongue and groove fit and are held together with a top plate.

The outer boards are held on by 6 screws although this one had only 5! There was a nicely repaired trace inside and so this side has been worked on. It appears that the transistors are all the originals and one had been removed to be checked. I'll have to check all of the emitter resistors and anything else in the path of the repaired trace just to be sure even though the channel works fine.

Should have mentioned these two caps from the amp module's top board in the last post. I had replaced one of them and when the other was pulled out I did a double take at the values. Beware if anyone ever recaps one of these!! Look closely and you'll see that they are two very different values.

Onwards to recapping the two boards and servicing the fan and then reassembly!

 

[crouse]

I am in awe of your skills. And Sarge looks like a hell of a dog.

 

[rBuckner]

Thanks for the compliment. That's 34 years of making mistakes and remembering what NOT to do! :thmbsp:

Sarge is the best dog we've ever had. Found as a stray down in Phoenix I think he has a profound sense of gratitude about having a stable home. Come by for a visit if you can, he'll roll over for a belly rub for ya.

 

[catrafter]

Great thread, I'm watching with much interest!

Tom

 

[Tube Sound]

Sarge is the best dog we've ever had. Found as a stray down in Phoenix I think he has a profound sense of gratitude about having a stable home. Come by for a visit if you can, he'll roll over for a belly rub for ya.

More pics of Sarge!! If I still lived in beautiful Prescott ('98 to '06) I would be on your doorstep pleading, with my 2500. Fortunately, a great tech is a bit closer here on the rock. Really enjoy watching this. :thmbsp:

 

[rBuckner]

I had to order more parts for the amp boards and had hoped they would get here in the usual two days from Mouser. FedEx, in their wisdom, decided to fly the box to Memphis and then truck them to Phoenix, the on up to here. These were shipped ground mind you. So that's taking a day longer. The package will be here tomorrow but I'm going out of town until Monday evening. Argh!

Time to play with the fan. First I scraped the old foam off of the gasket.

Then I installed new foam around the edge using household type weatherstripping.

Here's the cleaned up fan.

First the bearing cover / product label is removed.

Then you have to pick the glue off of the center plastic cap. I found it easiest to work from the inside.

The cover is off and is sitting upside down to the left.

The fan blade/rotor assembly is held in with a main e-ring and then a really small second one. I suppose this is to remove any slack. I had to relocate to my model building workbench to use a stereo microscope to get the mini e-ring off.

It bent a bit but it's off! I used some fine point tweezers and a small screwdriver to do the removal.

The main e-ring is a booger to get off but using some round tipped needlenose pliers to spread the ends and the tweezers to pop the other end off, I finally got it. I tried various tips on some automotive e-ring pliers and nothing worked.

Now the two major parts can be separated. Turns out this fan was really very clean inside. Visible on the rotor to the right are some thrust washers that pulled up when it was disassembled. There was definitely some fine oil on the washers. I cleaned out the bronze sleeve on the other side with a dry pipe cleaner and left the rotor side alone as there was nothing discolored or dirty looking about it. I blew the bronze bushing out with some canned air and using a toothpick dipped in fine oil just put a little bit back into the bushing.

I left the rotor on the table to keep the thrust washers in place and placed the other side back on. Then the main e-ring went back on then the mini ring which I had to flatten (did that in place) then squeezed it closed with the needlenose pliers. The plastic dust cap was set back on and some 12 minute epoxy was mixed and lightly applied around the perimeter. This was done with the cap in place.

Then the sticker was put back on, with a bit of the epoxy put on the back of it on the end away from the pull tab. Some epoxy oozed out but it was wiped away with a bit of paper towel. The green tape is just to hold it down while curing

BONUS SHOT!
I pulled the top plate off of the tunnel and separated the halves. Here's all the output transistors. Lo and behold, one was replaced with a NEC part. It is the same part number as the Marantz branded parts, 2SD555, so that's cool.

See y'all in a few days!

 

[pbda]

Marvelous photo essay...keep up the good work.

 

[rBuckner]

Alrightee, I got the parts in and now that I'm back in town, got the amp boards done. Along with the handful of electrolytics, I replaced the film caps with Panasonic stacked films. I also matched up a couple of sets of KSC1845's and replaced both channels' diff pairs. May as well as the amp section is a bit of work to get in and out.

Sorry, no pictures of it back together yet but it's working!

That concludes the board recapping. The main filters still need redone. I have the caps to restuff them which will retain the original look and provide a sturdy mounting. Still quite a bit to do but we'll get there.

 

[catrafter]

Nice!
Please post pictures of the cap restuffing for viewing while munching popcorn.

Tom

 

[rBuckner]

Will do. Make it caramel corn and I'll join ya!!

BTW, an observation on the 2500: None of the silkscreened cap polarities on the boards was wrong.

 

[rBuckner]

Decided to have a cleanup night tonight. Washed the face plate and the knobs with Windex and a toothbrush first. The did a power cord clean and inspection for any insulation issues and none were found. I polished the prongs with Flitz Polish. Also checked the main power fuse for correct value and it was fine. Here's some cleaning tips.

Stuff to clean and detail the rear panel.

The drill is used to polish the RCA jack shells. You cut a Q-Tip in half and chuck it up close to the bud. Then dab a touch of Flitz on it. Then just motor polish the shells. Add more Flitz after every other jack. The Q-Tips bust off after a bit, you'll go through some. After all are done use a clean Q-Tip (in the drill) to do the initial removal of powder then hand detail the area.

There, that's better!

I like to rust treat any of the black screws that need it. This unit doesn't have too much except for the fan mounting screws.

Dab it on with a toothpick.

All dry. It will have a flat finish. Some Armorall or the like will bring back some finish.

Rear panel completed. Gotta get that bit of paper towel off the lower left fan screw!

I use pipe cleaners and DeOxit to treat the RCA jacks' center contacts.

Bend them over on the end by about a 1/2". I will bend this over all the way in a sec.

Spray just a touch of DeOxit on the doubled up end and insert into the jack and swab it while twisting it. Add more cleaner after every 2-3 jacks.

Here's after cleaning about half of them. Snip off the end and rebend another to do the rest.

That's all for today!

 

[cbn700]

Thanks those are some very good cleaning tips to use while restoring or just cleaning up a newly purchased unit.

 

[mvandyke]

Great work - thanks for the pictures and the tips and tricks.

 

[crouse]

Thanks for the compliment. That's 34 years of making mistakes and remembering what NOT to do! :thmbsp:

Sarge is the best dog we've ever had. Found as a stray down in Phoenix I think he has a profound sense of gratitude about having a stable home. Come by for a visit if you can, he'll roll over for a belly rub for ya.

Strays are the best. I have a big black dog named Buddy who just showed up in the neighborhood when he was about 3 months old. 95 pounds of love.

 

[rBuckner]

I enjoyed doing some listening last night before starting to play with the dial LED conversion. It sounds really good to me with a very engaging sound. I cannot detect any difference when switching the tone control from "OUT" to "IN". All those new e-caps, film caps and polystyrenes have paid off I suppose.

Then I shut it off to pull the dial out and the fan rattled to a stop. Bummer! I'll have to pull that back out and play with it. I do have an ace in the hole in the form of a NOS fan still in the box. I got it when a company that I worked for was bought out in 1987 and they told us to keep anything we liked (besides test gear) from our workbenches so it was a part of the booty from that.

To start with the outer silver retainer was pulled. There's 4 screws: 3 sheet metal and one machine thread. This is correct.

The track for the dial pointer comes out next, 2 screws hold it in. I ran the pointer all the way to the right and slid the loosened track to the left to get the dial pointer into a little indentation which was just enough to get it popped off.

I "tuned" the dial pointer back to the middle more then propped it up on the top rail to get it out of the way. As you can see I already pried the plastic dial off. Use hard plastic or wooden tools as much as possible to avoid cracking or scratching it.

The old vellum doesn't look too bad in this shot. It will be replaced anyway of course.

Got the paper off and most of the adhesive scraped off. I haven't cleaned up the lamp housing yet. The housing does not have any melting or heat warpage. All but one of the bulbs were out and look original. The good one drew 200mA at 8V.

I had fooled around and did some lamp boards to use with the old lamp ends before, using the Vishay parts that can handle AC voltage but didn't like the flicker. So these boards are the next generation and have a small bridge rectifier and 220uF tantalum cap to provide DC voltage. The LEDs are Osram Duris E5's (2700K color temperature = warm white). I chose them for their larger radiating surface and fairly wide light dispersion. The resistor hanging way out is just in there to experiment with.

Here is a shot of the front with a replacement 8V/200mA bulb on the left and the new LED one on the right. It doesn't look as bright as the incandescent because it doesn't hit the lamp housing as much. The LEDs are running at about 6.5mA.

Here it is with the dial plastic and some new paper temporarily taped on the back. Digital cameras don't do blues very well and the LEDs on the right actually appear bluer in reality and the incandescent on the left more turquoise. I did use the "night landscape" mode which minimizes the attempt to brighten up the exposure as much.

Same setup but with lights out.

As fate would have it, I had enough parts to do 5 lamps but the 2500 has 6 lamps. An order to Mouser has been placed. I will be able to do around 20 I think. Having the correct resistor value I also got some 1/8 watt parts which is what I designed the board to take. I'll be sure to take a shot of the fished units when they're done.

I'm going to play around with a green and then an orange LED for the dial pointer (vs. the standard red one) for fun and see if the 2500's owner wants
a different color. The plan is to sell it but he may just change his mind after it's all done! All of the function LEDs are red too which is kind of boring. What do y'all think of some different colors in there? In that size I can get yellow and green.

In the meantime, it's back to pulling the rear chassis plate loose again and yanking the fan. Oh joy!!

 

[mech986]

Interesting LED boards you built there, Do you have a bunch of those and do they fit inside the old fuse lamp or do you attach to the fuse lamp holders directly? Looks like an elegant solution, saves a bunch of current draw as well.

 

[rBuckner]

I have some boards, maybe 20ish. The end caps come off old lamps, get cleaned out and a piece of bus wire solders first to the boards, then the end caps are installed, then the wire is bent over and soldered on the end cap. I may put these into a spare fuseholder to align the end caps and put some epoxy in to "pot" these into place. So, yes, they pop right into the existing lamp holders, either way, can't put them in wrong.