EEVBlog #492 - Vintage Motorola MicroTAC Mobile Phone Teardown

[EEVblog]

What was technology like inside a 1994 Motorola MicroTAC GSM mobile phone?

[Legit-Design]

I think you might be wrong about the "fake" antenna. Snap the "fake" antenna in half with cutters from several places and take pictures or video? It might be just passively coupled, as long as it has something conducting inside there is a theory for it to work.

[tnt]

They're not saw filters. The "big one" is a ceramic duplexer and the second smaller one is a ceramic filter. They split the antenna signal into the "Uplink/TX" and "Downlink/RX" band, and isolate the sensitive RX stuff (that tries to receive very faint signals) from the TX stuff (which transmits like 1W or 2W of RF power into the antenna).

In more modern phones, there is no duplexer for GSM. Simply because GSM has been designed specifically so that a phone doesn't need to be full duplex. The TX and RX slot are slightly shifted in time and so modern phone just have an antenna switch. I guess back in the days those switch weren't good enough ...

And that weird module you took apart, I would guess that it's the RF Power Amplifier.

[mikeselectricstuff]

This is a GSM phone, so no duplexer.
Analogue phones had duplexers, which were usually the biggest part by far in the phone. Amazing tech - they could keep the 100s of millwatts (on a handheld)  Tx power out of the -100dbm receive signal, which was  only ISTR something like 40MHz away - serious voodoo

[JOERGG]

Hello everybody,
this is my first post. The sliding button on the side of the phone releases the full size sim card, if i remember correctly.

[JOERGG]

And i guess that the little microswitch detects, if a sim card is insertet. Remember sim cards were full size those days, approxymately 85 mm x 54 mm.

[Slothie]

Came here to say the same as JOERGG. The sim card was the size of a credit card and slid into the slot in the bottom.

[EEVblog]

There are few too many annotations on this one, so I'll just do a re-upload.

[Pippy]

Yes that little RF board you removed is the TX RF power amplifier. The bigger multi wire bonded part is the TX PA output transistor and the other smaller gold ones with wire bonds are the driver transistors.

Showing my age and background here

[gnif]

There are few too many annotations on this one, so I'll just do a re-upload.

Damn, I was just about to watch it

[senso]

Just to say that the forum link doesn't work, the link points to this:
forum: https://www.eevblog.com/forum/blog/eevblog-492-vintage-motorola-microtac-mobile-phone-teardown/

And there are more dead links..

[gnif]

Just to say that the forum link doesn't work, the link points to this:
forum: https://www.eevblog.com/forum/blog/eevblog-492-vintage-motorola-microtac-mobile-phone-teardown/

And there are more dead links..

Works fine for me.

[Stonent]

9:17 my time was 2 hours ago.

[Stonent]

I think I got it..

[EEVblog]

9:17 my time was 2 hours ago.

It'll take 3 hours to upload, then some time to process on Youtube.

[Stonent]

9:17 my time was 2 hours ago.

It'll take 3 hours to upload, then some time to process on Youtube.

Dayum.  I gotta be up in 4 hours to drive 6 hours. 

What was wrong with the first revision?

[EEVblog]

What was wrong with the first revision?

A coupla silly errors and oversights.
I started adding annotations, but it was just as easy to simply reupload. It had only been live a few hours.

[tnt]

This is a GSM phone, so no duplexer.

Oh but it _is_. Look at it :



You can clearly see the antenna pad in the middle and the uplink/downlink pads on the sides.

As I said, I know that GSM doesn't need a duplexer and you can do without. But looks like on this phone, they choose to use one.

[DaedalusYoung]

I think you might be wrong about the "fake" antenna. Snap the "fake" antenna in half with cutters from several places and take pictures or video? It might be just passively coupled, as long as it has something conducting inside there is a theory for it to work.

According to Wikipedia, the antenna really is fake:

On all models, and unlike the Motorola DynaTAC, the plastic antenna served no functional purpose, and was strictly for aesthetics.

[Telequipment]

I'm curious, I've seen those blob type ic's/controllers type devices on other things, I guess there a one off item or can they be replaced. I'm referring to that black blob behind the display.
Paul

[Legit-Design]

I think you might be wrong about the "fake" antenna. Snap the "fake" antenna in half with cutters from several places and take pictures or video? It might be just passively coupled, as long as it has something conducting inside there is a theory for it to work.

According to Wikipedia, the antenna really is fake:

On all models, and unlike the Motorola DynaTAC, the plastic antenna served no functional purpose, and was strictly for aesthetics.

http://en.wikipedia.org/wiki/Motorola_MicroTAC

Dave updated his teardown with the antenna teardown, it's not just plastic.

I've seen things with same idea for usb 3G modems. http://cdn.entelectonline.co.za/wm-43814-cmsimages/A-ADPT-026%20Datasheet.pdf claims -4 dB coupling loss. Ofcourse with usb dongle you are going to have a high gain antenna on the other end of the coupler to defeat losses.

http://www.poyntingcommercial.com/directorylisting/displaycommercial.aspx?dirid=55#prodlist=1  (horrible website, have to scroll around to middle of the product slider)



Additional Information

This device couples to the modem internal antenna signal and diverts it to a booster antenna thereby ensuring better signal reception and ultimately better data throughput. The coupler is slid over the modem (see photos). You then connect the other end of coupler to one of our booster antennas via the SMA (female) connector. The booster antenna can be mounted on the outside of the building and pointed toward your closest cellular base station to ensure good reception. Features: Works with most USB and express card Modems Lightweight Robust Application: Connecting any 3G/HSDPA modem to a high gain antenna for improved range and data throughput.


same principle with rfid inductive coupling: http://rfid-handbook.de/about-rfid.html?showall=&start=1

Original wikipedia source of the fake claim: http://web.archive.org/web/20121001035225/http://www.retrobrick.com/motomicro.html
Thats for Analogue MicroTAC

Another puzzling design feature was the retractable aerial. In fact, the aerial does absolutely nothing as it is purely for show. The unit features an internal antenna, however, the pull up plastic was added after focus groups in the US felt that any phone should have a visible aerial. But for the country who put big big heavy metal fins on their cars in the 1950's to make them seem faster, this is not really surprising.

Clearly this GSM version has a functional antenna. Becareful with wikipedia quotes

[Telequipment]

I'm curious, I've seen those blob type ic's/controllers type devices on other things, I guess there a one off item or can they be replaced. I'm referring to that black blob behind the display.
Paul

It's normally just where the board manufacturer puts the chip die directly onto the board rather than use the normal pinned/smd package. If they blow then that's it, new board required.

I see, I've noticed them before on cheap watches, and a lot of my children's toys, that have broken they all seem to have the black blob of different sizes. Thanks for replying .

[G7PSK]

I had one of those motorola phones in late 1994. It was so deaf that I could stand underneath the cell phone mast and get no signal if I did get a signal someone with a car phone could drive by and take the signal from me as they had more transmit power.

i kept it until early 96 when while doing the accounts I found that the phone company had been double charging me with two direct debits so I cancelled both of them where upon the threatened to take me to court so I told them if they wanted too I would also take them to court for duplicating the direct debit last I heard from them they asked for the phone back so I sent it to them but first I played with some high voltage and the phone, never heard from them again and I did not get another mobile until 2000 by which time there was more masts and better phones. When I got that first phone I was assured that over 90% of the country was covered by the masts but when I research that claim I found that was by population and not area so places like Norfolk were hardly covered at all and we still have black holes for phones even now.

[mikeselectricstuff]

This is a GSM phone, so no duplexer.

Oh but it _is_. Look at it :



You can clearly see the antenna pad in the middle and the uplink/downlink pads on the sides.

As I said, I know that GSM doesn't need a duplexer and you can do without. But looks like on this phone, they choose to use one.

I suspect that's for bandpass filtering, but maybe based on an old diplexer design. Analogue diplexers were at least twice this size.

[JOERGG]

If there is no need for a duplexer for GSM as mentioned before, could the showed part have the function to secure the correct impedance when two antennas are plugged in and split the RF path to the second antenna? I am sure there is an extra antenna input beside the charger plugin, used for installation in cars for example, where an antenna on the roof was possible.

[nitro2k01]

The AT28C64 is actually an 8 kiB EEPROM, probably for storing settings. The other two memories are indeed OTPROMs.

[sonic]

Here is a scan of the PCB of my first mobile, datecode on the flash chip 1994. I lent it to a friend, and unfortunately he locked it accidentially. I guess if I'd tinker with the Microchip 24LC04B in the lower right corner...

[SeanB]

The filter is to keep the 2W of RF from blowing up the receive circuitry, even with a TX switch you need the directional cxoupler to reduce the power fed into the receive port to a low enough level so that the phone can receive data as soon as the TX pulse ends without the receiver being desensitised or overloaded. I had onre that was in an accident with our bike driver. He skidded along the road on it in hia pants p[ocket and aside from needing a new battery ( and new pants) it worked afterwards. The Panasonic phone he used later and did the same with was repaired, but the only parts reused were 4 screws in the case.

[victor]

It is fascinating how much electronics design changed. Nowadays you can have more advanced and simplistic designs due to integration.

I wonder if the charger is linear or switching was commons back then.

[brabus]

Very interesting teardown, needless to say! 

I wonder how much did that phone cost back in 1994. Anyone has an idea?

Price with and without accessories, of course!   

[mikeselectricstuff]

Very interesting teardown, needless to say! 

I wonder how much did that phone cost back in 1994. Anyone has an idea?

Well over $1000 - in the early days, phones were heavily subsidised and tied to contracts to make them appear more affordable.

[G7PSK]

I was told when I got mine that the price to bu outright was over £600-00. I do remember also that apart from the monthly rental calls were charged at £0.51p per minute outgoing and ££0.35p a minute incoming, making mobile calls very expensive, at the time I found that many of my clients would not call my mobile due to costs of the call even from a landline which was also £0.50p a minute

[Grapsus]

I have found some MicroTAC schematics over there :

http://www.hackcanada.com/blackcrawl/cell/motorola/tacschem.html

but it seems that those are for a 5000 series microTAC and Dave has a 7200 one. Some blocks are still similar, looks like a lot of integration has been done.

I don't really understand this discussion about the antenna "it's not electrically connected therefore it must be phony". Come on ! the vast majority of antennas have EM coupled parts, try to cut the metal rods on a Yaggi antenna and see if it works I bet the wire in the movable part is 16 cm which is half wave for GSM.

[amyk]

It is fascinating how much electronics design changed. Nowadays you can have more advanced and simplistic designs due to integration.

I wonder if the charger is linear or switching was commons back then.

For comparison here's what's inside a very basic GSM phone (yet still more featured), 19 years later: http://www.bunniestudios.com/blog/?p=3040

Linear was definitely more common back then.

[RupertGo]

It's not so much the extra integration that's the real stunner, it's the number of functional analogue and digital blocks that have been subsumed into DSP - leaving Moto's advantage of making all the chips as useful as Mullard's expertise in vavles.

The only reason I've got a Rigol scope and a Rigol spectrum analyser is that it would be commercial madness for Rigol to put both in one box. The engineering to do it and come in well under the combined cost of the two units isn't the problem. (That FFT function on the scope hasn't got a lot better, has it? Wonder why...)

At some point, your 500 MHz quad-input scope-cum-SA will be just another app you download over your millimetric-wave pervasive infrastructure wireless broadband - as an exercise in nostalgia...

[Ed.Kloonk]

That antenna did indeed provide an ounce of extra signal once extended. You could notice the call quality if you were in a fringe area and had the antenna down. Also if you had the antenna extended on the table the phone would have more chance of receiving a call rather than diverting to message bank.

After many uses, eventually the grip that holds the antenna up starts to fail and anyone who owned this phone will remember how you had to hold the phone in such a way to press at the bottom of the antenna to make it stay up.

Annoying.

The bottom connector is for the feature kits you could buy. Toward the end of it's life, my one got so expensive to replace batteries and since it was only used (and would only work) in the car, I bought what was called a battery eliminator. Plugged straight into the cig lighter.

[SeanB]

I modified one to use as an alarm dialler. Just powered it from a car charger without the battery and left the flip open and simply connected the signal via a relay and a pulse generator ( one capacitor in series with the coil) to press the call button, with the last dialled number being mine. Would check once a week or so ( on the way out) that the display just showed the usual and not a missed call ( either another person misdialled or a robocaller going through the database) so that it was ready. Tested every so often and it worked. PAYG sim lasted about 6 months between recharging with minimum ( gotta love cell networks charging you to give them money) amount. Never had the thing go off for actual alarms, just testing.

[Shred]

Classic. I have a scan of a sales brochure for the 7200 with the price hand written on it: AU$999.

Based on the awesome performance of the Motorola analogue phones and the fact that the batteries and chargers were interchangeable, I bought a Motorola 6200 as my first GSM mobile phone (the 6200 was the next model down from the 7200).  It was a huge mistake.  As an earlier poster said: the early Motorola GSM phones were as deaf as a post.  The voice quality was appalling and the battery life was about eight hours - provided I didn't make or receive any calls.  The damn thing basically lived in its charger and had to be repaired under warranty several times.

I replaced it with a fantastic Nokia and have never bought another Motorola phone.

[PChi]

Thanks for the tear down. It's amazing how far the technology has evolved.
The 'ring tones' from the buzzer are probably limited to a few different frequencies that could be programmed from a micro controller digital output. Some attempt may have been made to tune the buzzer resonance and the acoustic volume / case plastics to maximise volume. It will sound horrible, though possibly less annoying that some of the tunes sometimes chosen.

[Baliszoft]

I had the BOSCH version of this phone back then in 94 (cartel sc 2g2). It was a slightly cheaper model (without the folding flap), though these (including motorola) weren't *that* expensive in europe as far as i remember.

[sonic]

Here is a scan of the PCB of my first mobile, datecode on the chips 1994.

I pried off the metal cans and scanned the back side, too.

[Tepe]

Classic. I have a scan of a sales brochure for the 7200 with the price hand written on it: AU$999.

A Danish price list from the summer of '91 lists the Micro TAC at DKK 16990 + 25% VAT. Must be the NMT version and not GSM.


The Storno Personal was DKK 24900 + VAT in an ad from April 4, 1990.

[Spectreman]

Hi.  I am a newcomer to this forum, it' s great !
I have one of these Microtac 7200 phones myself, sadly is not working at all, does not power up
even with a good battery.  Not a very well made unit I must say.
I collect old mobile phones, mostly Motorola analogue mobiles.
Cheers, Chris.

[GregRexUzelac]

Very interesting teardown. Loved the bond wire RF work! Thanks, Dave.
At 26:15 where we see the charger PIC, I think C24 (near baby-blue colored rectangular part) is installing incorrectly, no? I guess C24 isn't that important.

[woo]

I had this same phone in the 90s (it followed the even clunkier Tac3000 bone/handlebar model), and when I finally tore it down, I didn't have any clue about RF/HF technology. Thanks for explaining that stuff 20 years later :3