The cover removed easily. It is metal with some kind of vinyl coating, doesn't ring much. It is held into place with screws and washers. Most tuners don't give you the washers. Marantz wants you to feel that this is an audiophile luxury tuner. Well that's only partly true actually.
At first glance, the top circuit board did not look adequate for a supertuner. But it's not the only board, it's merely the IF and AM Radio board. The AM radio being mostly handled by a chip, most of the board is for the IF stage, which is relatively the most impressive technical aspect of the tuner, and right up there at supertuner standards. The bottom of the chassis is also covered in boards not entirely visible from the top. So consider the entire unit having roughly two layers of circuit board across the entire width and depth. You are getting a lot of circuit board and parts for the original factory list of $600. But a lot is related to the gee whiz features and the scope. With a few exceptions, the actual parts and build quality is not as good as high end supertuners such as Pioneer F-26, Kenwood 600T, and McIntosh MR 78. The latter are like tuner jewelry compared with the Marantz, which looks a bit pedestrian in comparison. But that's not surprising. In 1978, an MR78 cost about 3 times as much as a 2130. And if you add in the McIntosh MPI3 scope, it would be 4 times as much. The Kenwood 600T is much higher build quality, especially in the RF stage, but lacks scope and in my opinion doesn't sound as good. I think of the Kenwood 600T as a failed experiment, the L-02T is their ultimate tuner, and it has both the build quality and the sonics (according to reports, I haven't heard one myself).
One exception to the pedestrian build quality being the SAW filters, even few supertuners have those. The IF is very nicely done, with separate narrow and wide paths. That allows for modifying the narrow path for better selectivity, and leaving the sonically critical wide alone. Both narrow and wide have their own SAW filters, which is why there are two. That enables them to correct the phase linearity of both paths independently. It looks like Marantz put more of their tuner budget into the IF stage than comparable tuners, and less into the RF. That's similar to the Marantz 10B and 20B. I am considering the KT-8300 to be a "comparable" tuner in technology, build, and cost, though I'm sure many would be upset by that comparison, many tuner fans would regard the KT-8300 as greatly superior, though audiophiles in general might prefer the Marantz.
And FWIW there are two transformers, with a separate one for the scope. They are not large transformers, but they are both shielded transformers. That's not unsual for good tuners. The transformer for the tuner looks like the one in the Charlie.
I haven't looked at the bottom boards yet, but looking at the schematic I got from Hifi Engine, the MPX is like Kenwood KT-8300, with Hitachi 11223 MPX chip connected to two external transistors for actual switching. The MPX board uses a 4558 for output amplification, and output through a 10uF capacitor and 3k resistor. Then there is a separate buffer board, which buffers output either from FM or AM sections, applying volume control, filtering, etc. It also uses a 4558 for amplification.
The least impressive looking thing is the 8 section tuning capacitor and front end section, which has 5 sections for FM and 3 for AM. It's relatively small compared with those in the big dog supertuners. It does have a cover, unusually open toward the front. The Kenwood KT-8300 has 6 gangs for FM, a step up. FWIW Marantz does give you two Mosfets, the first being dual gate for a kind of automatic sensitivity control. Many believe the best front end design uses only one RF amplifier. Two is kind of an easy way to get high sensitivity, but at the cost of slightly higher noise and high susceptibility to distortion in the RF stage. I can't be too critical of the Marantz on this, however, as the Pioneer F-26 also has two RF amplifier sections, and the gain control of the dual gate mosfet does help avoid overload. And even if the 5 RF gangs are small, they are still air capacitors which generally have much better characteristics than the varactors that have been used in almost all digitally tuned tuners, which means almost all tuners made since 1980.
Unlike previous Marantz scope tuners, there is no attempt to cover every circuit module in a metal box. But I think this tuner may have better actual circuitry, and the functions are separated into separate boards in such a way as to not need shielding as much. I do see two interesting shields. The gyro touch flyweel has a shield. That's a good idea, protect the tuner from being injected with noise conducted through the body of the user! There's also a shield protecting the scope adjustments from the scope transformer. But in daylight, I see it is not a metal shield but a piece of plastic. Perhaps the purpose is to keep dirt out of the scope controls.
I wouldn't say Marantz was ripping you off, quite the reverse, considering the scope and everything Marantz was probably barely breaking even on the production of this tuner, let alone its design. The scope alone with its own circuit board and power supply looks like it would cost $200-$500 in today's prices, and that has to be considered a major piece of what this tuner is about.
Nor did Marantz "not have a clue." With a MPX circuit similar to Kenwood KT-8300, and other aspects of the design, it looks like these designers knew what they were doing. They were making a nice sounding good performing tuner with a scope. I imagine that the designers may have even had a KT-8300 on hand, with the orders from management to make something slightly better, and the Marantz indeed has many slightly better specs, and includes a pilot canceling circuit which the KT-8300 did not have, having been introduced the year earlier. In fact, this tuner even looks a bit more like a Kenwood tuner than an older Marantz, lacking the fancy internal boxes of earlier Marantz tuners, and instead having layers of horizontal boards not unlike the Kenwood tuners of this time. For this unit, in 1978, the tuner race was at its peak, and Marantz was struggling to not be seen as tuner laggard, lots of money were spent on parts, design, and exterior appearance, little left for internal cosmetics. Was this tuner OEM'd to Kenwood? And at that time the Japanese hifi companies were in their most intense competition ever, so I doubt it. I noticed that with the exception of the dial light boards, all the other boards in the tuner do not use the old Standard Radio phenolic that was in my 2270 receiver. They use a newer lighter material, which looks a lot what Pioneer used in tuners like the TX-9500, though not the even more advanced yellow material Pioneer used in my F-26.
You have every right to question, however, whether you want about 1/3 of your tuner budget to go into the scope, which is really more fun than essential. And even into the relatively nice cosmetics, though they may actually be trailing in this price class. This is not anywhere near as glamorous as a Kenwood 600T. Once again, the money went into the scope, though money was spent on the somewhat gimmicky panel. It's gimmicky looking, I think, like a 1970's cadillac, but the front panel is actually slightly thicker than necessary and nicely satin gold anodized. That cost a few bucks. The display is a very nice plastic, a much nicer plastic than on early generations made by Marantz Japan. It's almost invisible, could be mistaken for glass, and there's not much visible from a distance but it actually covers a great deal of the upper panel. Because it's nearly invisible, you see right through to the fully finished metal. So that was a nice refinement of what Marantz Japan had been doing with earlier tuners, which had a much cheaper looking plastic dial, though what was needed was more like leaving the past behind, as was done with the Esdotec restyling which transmuted the 2130 to the ST-8.
I dislike the gaudyness, but it's completely functional and has a nice luxury feel. The knobs turn with oiled smoothness. But the the knobs and buttons are still the same old plastic with metal covering. Well maybe that's not high end, though perhaps it offers some advantage in electrical isolation.
As an earlier user of gyro touch tuning, from 1973-1979 (I started using KT-7500 in 1979), I quickly came to despise it. It's not really as convenient as having a knob. Humans naturally grasp things, so the best ergonomics come from things that rely on that, knobs and computer mouses. But I can live with it. It's less of an impediment for small movements across the dial.
If you have specific needs that require a strong FM front end, this may not work for you, but it works fine for me, I think, we'll see. I'm moving aside a much more expensive tuner, the MR 78. I think the MR 78 could be a winner with the right MPX adapter. I do have an MPX-100, but I think that's not really the best anymore. An analog multiplier or LA3450 would be a good start.