Marantz Repairs

This is not a repair manual. Laypersons should never carry out work on electrical devices themselves. There is a DANGER OF LIFE due to electric shock!

Smoking will damage your equipment! It is best not to start.

I am also (still) a smoker and therefore do not want to lecture anyone about their health. But who puts expensive high-end electronics in his stereo room and then blows his cigarette smoke on the devices for years should be clear what he does to his poor helpless “darlings”. By the way, in my rooms there is an absolute and strict smoking ban. Therefore, here now the smoking cessation picture series for HiFi lovers.

Pictures of the repair

The mighty device without lid. On the top left is a matchbox for size comparison (a cigarette would have been more appropriate). At the back right you can see the power amplifier, equipped with a tunnel heat sink, which fortunately works perfectly. By the way, Marantz calls the traditional construction of tunnel heat sink and fan “Exclusive Turbo-Flo Forced Air Cooling System”. In contrast, the designation “Thermal Core” introduced by Apple for the new Mac Pro is still really reserved for their tunnel heat sink. The stereo display still works perfectly, the displayed circle comes about when both channels are fed a sine tone of the same frequency, whereby the sine is shifted by 90 degrees on one channel. It should be noted that the oscilloscope tube is not installed rotated by 45 degrees as one might expect from a goniometer. This results in a 45 degree rotated line instead of a vertical one for a mono channel.

The Marantz 2500 receiver shown here works electronically perfectly, but the nicotine has left its traces: On the one hand, the silver optics are gone due to the yellowish tint, on the other hand, the Marantz 2500 has a fan. Thus, the smoke also gets to places that are normally spared. All kinds of contacts are affected here. The switch contacts at the chinch sockets of the power amplifier, all pots, switches, even the power switch doesn’t work as it should anymore. There is nothing easy about this unit at all, except removing the front panel. Two hex screws accessible from the front on both sides and two nuts on the middle potentiometers in the lower section and that’s it. On the picture furthermore the cover for the tube as well as the wheel for the tuner are already removed.
The front panels. The dirty cloth in the background (from another repair …) fortunately softens the shock effect a bit. The two glasses (made of plexiglass) look like smoked glass, but originally they are not. The stereo viewer is of course not so beautiful blue by nature. For this purpose, a blue foil is glued to the back of the dial. The circle that can be seen here on the foil is also dirt. Soapy water has failed here, but fortunately 70% alcohol dissolves the dirt and does not attack the blue foil. The flattened edge on the top right is intentional. This is where the incandescent lamp sits which illuminates the disk and thus the printed scale when the oscilloscope is turned on.
Much better! I thought that the plates are not yellow but silver. The exploded view of the front unit (and ONLY the front unit! Taken from the Marantz service manual). To get to the potentiometers and switches, almost everything has to be disassembled.

Board mikado and cable tangle

And this is how the beautiful unit looks without its front. Many cables are plugged in, but unfortunately not all. You could almost think that they soldered some cables to each module on purpose to make the repair not too easy. The connectors have no coding and can therefore be plugged in the wrong way. All components that could not be unplugged (most of them) are on top of the unit. The circuit board with the input selector switch (bottom left) cannot be removed with reasonable effort. In the background on the left is the tuner, in the middle is the power supply and on the right is the power amplifier. In front of the power amplifier is the relay + resistors for the soft start of the mains transformer. I would call the whole thing “board mikado”. No matter which component you want to access, you have to remove another one first, then another one and so on. Even if it is still so beautiful from the outside, the Marantz 2500 is definitely NOT service-friendly (when I think of the Telefunken TRX 2000/3000, for example. There are hinges to open the boards and the cables are partly laid in tubes, hachhhhh).

View from the side to the circuit board with the channel selector switch. The unit is not tinkered or similar. The photo shows the original state. Also the connector in the lower part, which sits crooked, has probably left the factory like this. A cable harness is something else, let’s call it a “cable tangle”. Once removed, the circuit board with the equalizer and the volume pot (at the front) makes a clear impression. The switches for the filters can be cleaned without disassembling (the PCB can be removed), the potentiometers can be desoldered easily, but they are pressed inside, so they can’t be removed.
This is how the selector switches (here for the input) look in the Marantz 2500. The construction comes from Alps. Since this switch has many dropouts, I would normally desolder it for cleaning and take it apart if possible, but… … this way the single boards with the contacts are soldered on. If it was only one layer, you would still have a chance, but with 4 layers it becomes unsightly, especially since you can’t easily get the circuit board with this switch out of the device.
The scale from inside. The rubber on the lower left holds the lamp for the stereo display. The bulb can be pulled out after loosening the glue. To clean the inside of the rubber housing, you have to detach it from the scale (also glued, of course) and then glue it again.The before photo of the reflector (above) I fortunately forgot, it was not pretty. And almost completely reassembled. The scale cable and the front panel are still missing.

The Marantz 2500 in new splendor

The scale bulbs

The backlight of the radio scale consists in the original of 8 pilot bulbs with 8 V / 200 mA. Unfortunately, this value is no longer regularly available. However, there are still the values 150 mA and 250 mA. On the internet (ebay) almost always 250 mA are offered. For this device I used 150 mA which is still available in regular catalogs (e.g. B├╝rklin). This ensures that no too high temperature damages the scale reflector or a too high current shortens the life of the power supply. I find the lighting effect absolutely satisfactory. The stereo light as well as the scale light of the oscilloscope are of the type 8V / 60 mA, diameter rnd. 4,5 mm, conditioned. Unfortunately, this value is also very difficult to get. Alternatively the value 40 mA with diameter 4,2 is still available. These bulbs are available, for example, in this very nicely sorted ebay-shop. << back to the gallery Marantz Repairs.

Leave a comment

Your email address will not be published. Required fields are marked *