MDO4000 RF “Reverse Engineering”

After Dave’s Tektronix MDO 4000 teardown I decided to try to reverse-engineer its spectrum analyzer PCB. I used Dave’s high resolution photos (from his Flickr), my general RF knowledge and one of Dave’s post comment, by “Carlos” (helpful, thanks!).
My last work consisted of RF maintenance and design, with a large range of frequencies, so the block diagram I made shouldn’t be too off from the reality.
MDO4000 RF section

I think I got the most of the PCB. A lot of parts are from Hittite (RF switches, amps, VCOs and Log detector). I omitted some minor parts (DC and AC blocking for example). Unfortunately, I wasn’t able to find the I/Q analog-to-digital converter. Maybe it’s under one of the shielded cans or on an other PCB. As it’s a 10GSpS, it must have direct access to a memory of any sort, so it could be close to the main processor/FPGA.

Schematics (pdf):

MDO4000 RF Block Diagram

Photo with the numbers matching the schematics (pdf, 6Mb):

MDO4000 Photo with numbers for the Block Schematics

Block schematics with PCB components thumbnails (pdf, 9Mb):

MDO4000 RF Block Diagram with Thumbnails

If you find any error or want to add comments to the schematics I made, don’t hesitate to comment!!


Modding a Vintage Marantz 4240 Amplifier / Receiver to add a Remote Control

I already posted this mod on various forums and had Hackaday article written about it, but I thought it would be cool to write a few words about it here.

Marantz 4240 Quadriaradial Receiver

I got it broken, so cheap and repaired it (power amp transistors dead). Then, I decided to add a remote control by motorizing the knobs.

And how it’s made inside:

You can download a pdf document describing the electronics and mechanics here:

PDF Document (8Mb)

The next step of this project will be to make a standalone remote control. I already have some ideas (RF link, controls on a touch sensitive surface, LED feedback), but I have to find a solution for the casing. Maybe something 3D-printed.

Altium DRC settings for iTeadStudio PCB service

Just a quick informative note with my Design Rules settings for the iTead Studio PCB service, with Altium.

Altium Design Rules For iTeadStudio

Electrical Minimum Clearance: 0.2mm

Routing Width: 0.2mm

Routing Corners: 2,54, 45° (not really relevant)

Routing Vias: Minimum Diameter: 0.5mm; Minimum Via Hole Size: 0.3mm Preferred: 0.35mm

Solder Mask Expansion: 0.1mm

Power Plane Connect: Conductor Width: 0.3mm Air-Gap:0.3mm Expansion: 0.5mm

Power Plane Clearance: 0.5mm

Polygon Connect: Conductor Width: 0.3mm

Manufacturing Hole Size: Minimum: 0.3mm

Hole to Hole Clearance: 0.2mm

Minimum Solder Mask Sliver: 0.1mm

Silkscreen over Component Pads: 0.15mm (actually, should be rather 0, as the silkscreen isn’t (or shouldn’t be) printed on pads)

Silk To Silk Clearance: 0.1mm

Also, don’t forget the minimum Soldermask line width is 0.1mm (for text and drawings)


Sorry for the metrical system impaired people. As you can see, these settings are a little bit tighter than the ones specified by iTeadStudio, to go along with their “6mil (recommended >8mil)” funny sentence. Well, not really, as 0.2mm are equivalent to 7.87mils but it worked for me. Maybe the 0.35mm/0.5mm vias are borderline. If you want to be sure about the results (and not get the Fab people angry), you should make it more 0.35mm/0.6mm or 0.3mm/0.7mm, as there’s a 0.09mm tolerance in the hole registration and diameter.

For Gerber generation, I use the default settings, with the 2:3 and inches option. Don’t forget to select only the layers you use (top/bottom, Silk top/Silk bottom, Solder top/Solder bottom) and the RS274X format.

If my second batch of boards have a problem, I’ll update this post.

As last advice, I’d say to not rely on your power plane connections (if you poor a power plane on your board), but to make connections with tracks first and only then poor the power plane, so you’re sure that you’re within the minimum width/spacing specs.

Vintage headphones mod

Two years ago at work, I saved those French brand LEM DR80CR headphones form the bin (I work at an airport).

LEM DR 80 CR Headphones Senheiser modded

After opening them up and checking the available space in the earcups, I decided to upgrade them for Hi-Fi. The original earcups contained crappy 8 ohm speakers, like the ones in cheap alarm clocks, impedance-balanced with a small transformer. (The primary purpose of the headphones was to listen to air traffic radio, not music).

LEM DR 80 CR Senheiser modded

Then, I bought Sennheiser HD205 headphones. They have a good quality sound with compact and comfortable earpads. (Unfortunately, I don’t have any photo of the teardown, but the build quality is good, lots of screws and superior moulded hard plastic). They’re more than enough for music listening. Any headphones above $200 are just a rip-off (unless they have other features than just music reproduction)

Sennheiser HD_205_II

The LEM headphones have removable imitation leather earpads. Under them, I found an aluminium gird plate where the speakers were attached to. The gird was riveted to the earcups plastic.

LEM Headphones Sennheiser

First, I removed the speakers, the transformer and all the original parts, leaving only the wires running from one earcup to the other. I cut out an opening in the aluminium gird where I could fit the Sennheiser earcups. I had to cut off some plastic, but I could leave the screw wells and the leather/foam ear cushions plus the plastic assembly that is volume-matched with the speakers.

LEM Headphones Sennheiser

I made holes for screws in the aluminium gird, to be able to attach the Sennheiser speakers to. I had to make small pieces of soft plastic to link the speakers to the gird. They also act kind of springs and cancel vibrations.

LEM Headphones Sennheiser

I also left the Sennheiser wire and jack plug. I’m still looking for a nicer one, that would be spring-shaped with a fabric ext. insulation (if someone have brand names…).

Was it worth it?

Totally! The LEM headphones have a unique vintage look (I did the mod before the vintage-headphones-signed-by-famous-douchebags started to be sooo popular), combined with the great Sennheiser sound quality. Plus, they now have a greater noise isolation due to the double earpads (it’s almost dangerous to walk on the street, as I barely hear cars coming) and stay pretty comfortable to wear, even several hours in a row.

On a more electronics-focused side, there’s plenty of room in the earcups to fit batteries and circuits to make for example, a Bluetooth version.

In conclusion, except for the jack cable I still have to find, it’s a complete win!

iTeadStudio PCB test: Populating the board

After I received the PCB ordered form iTeadStudio last week, I soldered the components today.

So far, everything related to the quality of the PCB looks fine. The footprints match, the FR4 substrate handles the temperature well (1 mm thick option) and the HASL finish is ok and easy to solder on. It changes from my hand-etched PCBs.

GIF animation of an USB board soldering

I successfully programmed the PIC with Microchip’s USB device example firmware.

Unfortunately, the board wasn’t recognized once plugged. The LEDs were blinking, but nothing in the USB device list. After some investigation and noticing that the LEDs were brighter when the board was powered by USB than with the external power supply jack, I found the problem: I have dyslexia.

IteadStudio PCB Test: USB board TOP

Or rather, let’s say: “Don’t name you schematic nets with names that one could mix up” Indeed, in the schematics I inspired myself from, there were two different nets with very close names. One called “Vbus” and the other “Vusb” all written with caps / small caps. And of course, I connected the Vbus to the Vusb and when powered with USB cable, the 3,3V regulator was by-passed and the PIC was fed +5V directly to its “VUSB” pin.

IteadStudio PCB Test: USB board BOTTOM

Luckily, the PIC didn’t die, even if +5V is over its maximum voltage rating. The PCB was easy to fix by cutting a track, adding a wire and de-soldering a diode. Unfortunately now I have to be careful to not plug an external power supply when my board is plugged to a computer (no more protection preventing back feeding of current to the USB cable). Well, I should live with it.

USB dev board iTeadStudio PCB

This board is inspired form Microchip’s FS USB plug-in board. I added a Texas Instrument’s RS232 transceiver (MAX3221), three LEDs, three push buttons and connectors with the six GPIO ports from the PIC.

I’ll play with it now to see what I can do with USB and all those GPIOs.

Testing iTead Studio PCB service.

Few months ago, opened one of the cheapest PCB making service of the web. They claim a 6/6mil and 0,3mm hole size specs. Two layers with top and bottom silkscreen, soldermask for everyone, Woohoo! Their prices start at $12 for ten pieces of a 5x5cm PCB plus $4 shipping (in my case, to France). They even have a special offer right now at $9.90 for 10 pieces of 5x5cm PCB. And for $10 more, you get all the boards e-tested (“only” half of them are e-tested for free).

It seems like it’s not worth any more to bother with home made etching for small boards, for that price! (I pay something like 9 Euros for a 120×150 blank FR4 board (w/o shipping) and I have to make vias myself and of course, no silkscreen, no soldermask)

I needed to make a 120×150 PCB with features impossible to achieve without real vias, so I decided to test iTead Studio with a small 5x5cm board. For a long time, I also wanted to learn USB programming with PICs and to use Altium designer. Three good reasons to try the Chinese fab.

I adapted Microchip’s USB demo board schematics, the one with a 18f87J50 microcontroller and threw the components on the board (after some nights spent with Altium tutorials. Argh, libraries.)

I used the following design rules: track width: 0,2mm. Vias diam:0,5mm. Vias holes: 0,35mm. Solder mask extension:0,1mm. Minimum soldermask sliver: 0,1mm. Silk/Silk: 0,1mm. iTeadStudio advises to not go as low as 6/6mil, but try to use 8/8mil rules. Some people (like Dave Jones from had a bad experience with the fab changing his gerbers, but it was before they updated their fab rules.

After checking and double checking my gerbers (it was the first time I sent something to a fab), I ordered and paid for the 5x5x10 PCB service the 24/08/2011 @1:50pm (local times). My order was confirmed ten minutes later, with the address to send my gerbers to, what I did @ 2pm ; the two copper layers, two silk layers, two soldermask layers and the drill file, all zipped and labelled as instructed on the website. I received an answer the 25/08 @4am, saying they submitted my files to the fab and that they’ll keep me updated if there’s a problem. Apparently, my files were all right, because the next iTeadStudio mail was on the 30/08/2011 @3:30pm with a tracking number for my PCBs (I took the air mail shipping, for $4).

The tracking number worked two days later:

iTeadStudio Shipping Tracking

Actually, you only get the tracking inside China (at least in my case with France as for destination)

The package was delivered to me on the 09/09/2011. That’s one week shipping, which is really fast! As the value was small, I apparently didn’t have any trouble with French customs.

Cute Package From iTeadStudio

I got twelve PCB. Six of them have a mark on the side meaning they passed the e-test:

iTeadStudio 5x5cm PCBs

After a quick visual inspection, I noticed a suspicious track on one of the e-tested boards but I checked it myself and it’s ok. An other e-tested board has its silkscreen erased on a 1cm wide band.

e-tested board (top):

iTeadStudio PCB e-tested

(I didn’t take the time to tidy my routing as I usually do. I also forgot to configure the GND poor to integrate all the GND tracks). The board edges could be better, but maybe the rounded corners I defined were too small. I tried tenting on some vias (to see if they would make it). It worked, they’re on the extreme right side and one under the S1 switch. I didn’t try NPTH, I’ll do it next time (but I don’t see why it wouldn’t work, they’re offering to drill slots)

Here, the board with superposed picture from Altium:

iTeadStudio PCB with Altium image superposed

As you can see, there’s a tiny offset in the silk printing and the soldermask is a bit strange (it overlaps on the vias). Apart from that, it’s perfect.

Gif animation (click to open):

View of a non e-tested PCB:

iTeadStudio PCB NON e-tested

You’ll notice the shorts on the upper left corner and under S1. If it’s the only errors, it will be easy to fix.  An other non e-tested board has a line of shorts on the big chip footprint (un-fixable). Actually, it looks like a hair on the photomask 🙂

Except these two PCBs, the other non-tested ones look quite OK. I’ll check them if I have time.


Is it worth it?

I’d say YES! Even if you need only one or two boards, it’s still less pain than to etch them yourself. And you’ll have a real silkscreen, a real soldermask and real vias! Even for larger boards, it’s still worth it, in my opinion. You should maybe consider buying the $10 100% e-test when you start to exceed the 10x10cm dimensions. If you’re a hobbyist or even an advanced hobbyist, you’ll be able to have enough-quality PCBs for very cheap. If you’re a professional, maybe you should consider a fab closer from your country, one you can directly talk with, but I’d say iTeadStudio could even be used for the first prototypes. If you have time to wait for the shipping.

All in all, the fabrication and shipping took 16 days, including two weekends. It’s really not bad, but maybe I was lucky. More expensive or bigger orders could be checked more carefully by your country’s customs.

So, where’s the catch?

Well, if I look at the boards, I don’t see any catch. You get what you pay for, even a little more. There’s also SeeedStudio offering the same PCB services and some people were saying iTeadStudio and Seeed use the same fab (makes sense, same price, same options, same DRC rules). It’s the first service for proto boards with such small prices I ever see. I suspect the fab is making those PCBs at the same time as other more legit orders and uses the available room on the boards to process the prototypes. Also, they seem to print as many boards as it takes to reach the 50% OK e-test (I got 12 boards).

But once again, I base my thoughts on the only order I passed and the first one. I’ll update this article when I order more boards. And also when I’ll solder the components on the boards I just got.


[UPDATE]: See then new post about fitting components on the board.