Welcome to the restoration tutorials from the "classic" irebuildmarantz.com website. These how-to guides have encouraged and enabled countless newbies to rebuild their own Marantz stereos, myself included. Some of the methods shown would not be considered best practices today, but the guides are still useful after all these years. Thanks to Robert D. Bowdish for creating them. 
irebuildmarantz.com is a terrific place to find parts for your 2235B
All LED Kits for your 2235B Reproduction feet for Marantz 2235B Replacement power switch for Marantz 2235B
All LED Kits Reproduction feet Power switch

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Model: 2235B

This page will get you started on rebuilding/restoring your Marantz receiver!

The intention of this site is to show how to replace the old electrolytic capacitors in Marantz receivers that have likely dried up over the years to restore proper functionality. This site will also show the proper steps to perform bias and DC idle current adjustments on the Marantz 2235B receiver.

I will be repairing my 2235B model in the following photos but you should be able to do virtually any Marantz receiver by generally following this guide, however the bias settings we will be performing and the parts we will be replacing are tailored to the 2235B.

Just to let you know, I am an electronic technician and engineer and have been working in the broadcast equipment manufacturing sector for over 20 years, so you can rest assured that I know what I am doing. I have restored and/or repaired hundreds of electronics devices over the years. I've worked on and personally aligned audio equipment for places like Skywalker Sound in Marin County, CA, Paul Allen's offices in Seattle, WA, Bill Gate's residence in Redmond, WA, just to name a few. You are in good hands here :-)

I will be assuming that you know how to solder and desolder on printed circuit boards, have basic understanding of electronics and electronic components and the tools shown below, and have a decent amount of common sense. I hope I haven't assumed too much. If you have questions or get stuck somewhere, just email me here info@irebuildmarantz.com Use the word "marantz " somewhere in your subject line so the spam blocker doesn't eat your message, and I will do my best to help you.

PLEASE PLEASE PLEASE, if you are headed out the door right now to buy your first soldering iron and solder with the idea that you are going to learn how to solder and repair your Marantz from this website, STOP RIGHT THERE!! Do not attemp any of the repairs on any page in this website if you have not previously had extensive soldering experience. Now, you do not have to be a full fledged engineer to work on your receiver, you do have to know how to produce very solid solder connections, however, and that only comes with plenty of soldering experience. You can very easily destroy your receiver or at least make it worse than it was by simply not knowing how to solder properly, not knowing how to use soldering tools effectively, not using the correct type of solder, the correct type of iron, the correct temperature, etc. If you still think you can do this project as a first time electronics experience, email me first and let's talk about it, BUT BY NO MEANS REMOVE ANY COVER OF THE RECEIVER, OK?

Moving on....

Ok , some things you will need before we get started:

A service manual PDF scan for most models (complete with schematics and parts list) are available for download for free at HiFiEngine.com. High quality paid scans are available for a modest cost from vintage-electronics.net.

Dried up capacitor

(a note about bad caps)





Your Tools:
Soldering Iron
Multimeter (DVM)

Solder Remover
Solder Wick
This is ok, too
But this is NOT ok
Here are the parts you will need: (35 caps, low leakage electrolytic. Available here at a resonable price.)

1 uf/50v (4) 1 uf/25v (4) .22 uf/50v (2) .22 uf/35v (2) 3.3 uf/25v (2) 4.7 uf/25v (2) 4.7 uf/50v ( 1) 22 uf/35v (1)

33 uf/50v (2) 47 uf/16v (3) 47 uf/50v (2) 100 uf/50v (1) 220 uf/10v (1) 220 uf/35v (1) 220 uf/50v (2) 220 uf/63v (1)

330 uf/50v (1) 470 uf/16v (1) 10000uf/50 (2)

Ok, before we get started a few words: First and foremost, DO NOT ATTEMPT TO REPAIR YOUR RECEIVER WHILE IT IS PLUGGED INTO THE WALL. You would be surprised at how easy it is to forget to unplug the unit and how many people get zapped these days. Next, don't fool yourself. If you don't have the tools or know-how to unsolder and resolder new parts into a printed circuit board, you are best to leave these repairs to someone who does. You could easily make scrap out of your Marantz by not knowing what you are doing. Make sure your solder is NOT acid core. Take that roll and put it with your plumbing stuff and go get some good rosin core solder (or mildly active, organic flux solder is best). Not sure? ask me: info@irebuildmarantz.com use the subject "Marantz questions". Personally, I use a quality eutectic solder (63/37) with rosin flux (yes, it IS important!). Eutectic solder has the narrowest plastic range which yields the best connections with hand repair work. You however might like to use silver solder in your work. Nice call you HIFI tweak! ;-)
Once you have your tools ready, prep your receiver by first unplugging it from the wall (Have I made my point yet?). Prepare a work area by laying down some cardboard on your kitchen table, or use your shop work area that is well lighted. Remove both top and bottom covers from the receiver and set aside. I use an old film canister to hold the screws so they don't get lost. You may want to blow the unit out with compressed air at this point (or use a vacuum cleaner) to remove accumulated dust.

I will be starting with the power supply and moving through the receiver and finally ending with the power amp. Because the AM and FM circuits will require realignment which is way out of the scope of this website, I will not be attempting any changes there (I also don't use the phono preamp, so I will not be working on that circuit either). You should decide if your receiver is functioning well enough in these areas before working in these circuits. And you should refer to qualified personell with the required tools to perform the alignments (you don't have them, ok?).

This site's purpose is really to restore the primary audio path through the amplifier to provide better security against a future component failure due to failed electrolytic capacitors, and as a result move toward a receiver that is closer to the original design specs.

Ok, let's get started. Take your component cleaner (make sure it is the correct cleaner for potentiometers and switches. Be aware the wrong stuff can ruin your pots! I have used Radio Shack 64-4315 safely, for instance) and soak each switch while working the switch in and out multiple times. Do each switch one at at time. When you are satisfied you have worked it enough, move to the rotary switches and soak and work them over their entire range multiple times. Then move on to each potentiomenter (bass, treble, volume) doing the same. You will likely have to use the adapter tube to get the fluid into the potentiometer. You want the cleaner to get into the canister of the pot itself to clean the inside. Don't forget the balance control. You can access it through the front of the receiver's face.
Cleaning pots and switches
Now I am going to replace the main power supply capacitors. I am going to start with the 2 large filter caps C001 and C002 (on the schematic) since they are a good place to start and they are the most easily accessible. If you are planning to go through and replace all the electrolytics following the procedure on this site, you may want to highlight each part on the schematic (8.3Mb) as you replace the part. I also highly recommend verifying the value of the new part before you install it into the receiver. Here is also an XL spreadsheet with all the caps we will be replacing.
Replacing power supply caps.
Just keep pulling the solder out of the connection until you can free up the capacitor.

Note the polarity here. Both caps' negative terminal are pointed towards the rear of the receiver.

Notice the difference in manufacturing over the last 30 years? These caps are both the same value.

Beware, you might want to install larger caps to take advantage of the additional room. This will put undue stress on the upstream power supply and could cause serious problems. Better to stay with the original design values.

Now, working on the power supply PC board:

Heat the solder at the connection to the circuit board on the solder side and using your solder sucker, remove the solder from each leg of the component to be replaced. You may want to remove any excess solder afterward using solder wick. Old solder leaches copper from the PC board which deteriorates the intermetallic bond so it is recommended that all old solder be removed when replacing parts.

Measure the new part if possible before installing it. Remove the old part and replace it with the new one, pushing it gently down against the PC board. Note the polarity of the device. Electrolytics explode like firecrackers if you install them backwards! You don't want a surprise later when you power the unit, so get this one right the first time.

Now resolder the leads, adding solder slowly and letting the solder flow. Then remove the heat and let it cool making sure not to disturb the joint until it is solid. When you are satisfied with the connection, use your cutters to remove the excess leads (don't cut into the solder!). You may want to clean your work with Alcohol and a cotton swab (or I use an old toothbrush), that is fine. The flux in your solder may or may not need to be removed. Check with the manufacturer of the solder to be sure. This is important as some fluxes are very active and can harm the metals if not removed.

Now mark that cap with your highlighter pen on the schematic and move to the next cap on the list for this board.

Moving on to the tone control board:

This board may require some mechanical disassembly to get access to the component side. You will need to remove all the control knobs (they just pull off) and the front face (a great time to clean them BTW) to remove this board. Then you will need to remove all the hardware holding the pots and the board. (sorry, no pictures) Use caution not to damage the wires or parts as you remove this board. We will be changing 11 caps on this board.

Be sure to reassemble in reverse order of removal.

Now we can do the next 2 boards:

The PH01 board, which has 2 caps and the PC01 board which has 4 caps. Remove the screws that hold the board. Only remove wires as necessary to get into the space needed to swap out the caps. (sorry, no pics here yet, either)

And lastly, the power amp capacitors. There are 8 caps that are critical in this circuit. Be extra careful to get polarity and voltage values correct here. A mistake will likely cause catastrophic damage to the amplifier. Un screw the hold downs and lift out the amp, heatsink and all. Remove the screws that hold the board to the heatsink. You might have to unwire some of the connections to get to the work area. Use masking tape to lable these if required. (sorry no pics yet)
Make a quick but thourough inspection of your work and rework any areas that you were not happy with. Once you are sure that all is perfect, reassemble all mechanical components as necessary but hold off on reinstalling the covers to the receiver.

At this point I like to clean up my area and put away my soldering tools. It gives me time to go over the repairs in my head. You never know, you might have missed something and remember it now. A hasty power test can be a bad thing. I understand the excitement but go ahead and take the 10 minutes it takes to clean up to make sure in your own mind that all is done and done right.

Beware: The following tests will require the receiver to be powered up and could result in electric shock if you put your skin where it doesn't belong. Don't put your hands (or other body parts) anywhere inside the unit that doesn't require it!! Move slowly and deliberatly to the task at hand. Be aware of the over 100VDC potential that exists inside the device and where those potentials exists!

If you don't know what you are doing, YOU COULD BE KILLED! Although most of the circuits are running on 35VDC or less, you could still get a good shock and that is no fun. Just take your time and follow my instructions carefully (remember the old Operation game?) and all will go just fine!!

OK? Let's go:

Power test the unit: Without connecting anything to the receiver, power on the unit. Be very aware of strange odors, smoke, noises, dimming of the lights. If anything out of the ordinary happens, quickly kill the power and inspect. Did you put a cap in backwards somewhere? DId you squish a wire between 2 parts? These things happen.

Upon power you should hear the speaker protection relay engage the speaker circuit, the familiar "click". Did you hear it? Yes, continue on at the next Purple words. NO?, stop at "No click? STOP!!!!" below.

No Click? STOP!!!!!!! What to do? You powered it up and it is just sitting there staring at you. Well, this means that the speaker protection circuit has determined that there is sufficient DC at the output to damage your speakers and has, thus, opened the output to protect them. If this problem was not there before, it means one of 2 things. Either the bias is off enough to engage the protection circuit, or there are more serious problems like a backwards cap, solder bridge, somethinge else. Power down and reinspect your work. Email me if you need to and I will help if I can.


If all is well, we will now proceed to the bias asjustment phase of our project. (Special thanks goes out to Brandon for supplying the schematic and bias instructions. Cheers!)

If you feel everything is ok but the protection relay still doesn't engage, we can go around the relay and make the first adjustments (this will likely fix the problem). Connect the DVM (set to DC volts) to test point 809 (+) and 805 (-) on the power supply board and adjust R713 on the power amp board for 0VDC reading on the DVM.

Move the red DVM lead over to test point 810 and adjust R714 on the power amp board for 0VDC reading on the DVM. You will probably hear the familiar protection relay "click" at some point in the adjustment as you get things into spec. This is what you want. If all went well, you can make the remaining adjustments following the procedure starting with the green words below. If you still have problems, or can't make the adjustments within the range of the potentiometer, you will have to stop here and troubleshoot...

My DVM died during this repair so I had to drag out the scope for the bias settings.

Don't worry, just follow the directions using your DVM.

Connect DVM to the Left channel output terminals (speaker outputs) black on black or ground. It is of course important to turn on the speaker outputs, so engage the Main speaker switch at the front panel, and connect the DVM to the Main speaker terminals. If you heard no click of the speaker protection relay when initally powering the unit, you will be reading an open circuit which is not what you want to do. (see "no click "above)

Adjust R713, for 0 VDC.

Move the DVM leads to the Right channel Main speaker terminals and adjust R714 for 0 VDC

Connect a DVM between J713 and J717 on the power amp board.

Adjust R766, for 8mVDC.

Repeat for other channel (J 718 and J714.)

Repeat after 30 minutes (after the amp has time to warm up to normal operating temperature)

Connect a DVM between J804 and J805.

Adjust R806, for 35VDC.

That's it.. We're done!!

At this point you may want to replace burned out lamps, and do any other repairs and additional cleaning before replacing the covers.
Once you feel that the unit is ready to put back into use, replace the covers and reconnect to your speakers and inputs. Listen for any strange sounds, pops or things out of the ordinary. If she is running well, give her a good test and see how she does. You might want to recheck the adjustments in a few days for any drifting. Other than that, you are likely ready for another 30 years of great sound and enjoyment from your Marantz receiver.

Some people feel very strongly about the sound of silver mica capacitors. You might want to consider changing the remaining ceramic caps to foil caps to continue with the spirit of this website. There are many other considerations (like precision resistors and such) that are beyond this sites scope but hold equal importance in the continuing persuit of the longevity of these amplifiers. If I can be of any assitance in following this road, just email me and I will aid you in any way I can.

Good luck and thanks for keeping these HIFI legends alive!