Author Topic: EEVblog #433 - Mailbag  (Read 5069 times)

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Offline EEVblog

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Offline PbFoot

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Re: EEVblog #433 - Mailbag
« Reply #1 on: March 02, 2013, 12:10:54 am »
On those old Motorola phones, you can access the service mode in the following way:

Take off the battery, and look at the contacts. There are three. Compare them to the matching contacts on the phone. You will see that the two outside ones have protruding contacts, while the middle one is flush on both the battery and the phone. Under normal conditions, the center contacts are never made. Take a tiny bit of conductive material, such a aluminium foil, and make a little "cigar" out of it so it sits in the groove where the center contact is on the phone. Then carefully reinstall the battery so as not to knock the little cigar out of place. This way, all three contacts are made. When the phone is powered up, it will be in service mode. Older versions of the phone firmware would actually allow manual tuning of the receiver, so you could listen in too phone calls (on the old analog AMPS version.) You can also see the hexadecimal identifier of the cell you are on, precise signal strength, display test, keypad test etc.

The way the contacts were originally intended to be used, a service tech would have a special "dummy" battery that had all three contacts in place, and a lead that could go to a bench power supply.

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Offline T4P

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Re: EEVblog #433 - Mailbag
« Reply #2 on: March 02, 2013, 06:30:58 am »
I bought the same weighing scale as Dave  :P
Seller says up to 3kg but it goes up to 10kg  :o
 

Offline Ed.Kloonk

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Re: EEVblog #433 - Mailbag
« Reply #3 on: March 02, 2013, 09:52:45 am »
That very same microtac 7200 was my first phone also. It was a GSM (digital) phone when the previous models here in AUS were the analogue and were far superior. I bought mine from tricky dicks in May '95 and got suckered into the whole Digital system when it was in fact hopeless compared to my colleagues who had analogue microtacs.

The only other difference is this model had a LCD screen where as the analog ones had a single line led display. The 7200 was a POS! (imo). Promised by telstra that the GSM coverage would improve. it didn't. Persevered for about four years with it until Nokia came around. The Nokia I replaced it with was smaller and worked much better signal and battery wise.

The term "Mobile phone". I remember first being used on the radio by Telstra. They were appealing to the trades and suggesting that those who could be called by customers anytime were more likely to get work. I found it to be a god-damn leash.

The batteries for it. They were a nicad initially but had nasty memory effect if you didn't run them all the way down. There were a few sizes. The one you've got in the mailbag is the 'slim' type and I found it only lasted five hours because the phone was constantly hunting for towers. A battery twice the size, capacity and weight became available and made the phone awfully big and heavy.

The NiMH batteries came on the market shortly after and were slightly lighter than the nicads. At last no memory effect and you could re-charge if, for example, going to work in the morning, come home for an hour or so and top-up the battery and go out in the evening. Then do a full charge of both batteries that night.

The antenna used to 'slip' after a while and you'd be on a call and have to hold the antenna up with your pinky. The Nokia I got after this phone had no antenna and worked better. Nar that phone was a expensive pile of crap. Motorola went backwards with that model. The one before it was owned by one of my colleagues from 1994 right up until 2000 when they canned the analog system. I couldn't wait to be rid of mine.


 :)


 
« Last Edit: March 02, 2013, 09:55:11 am by Ed.Kloonk »
 

Offline robrenz

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Re: EEVblog #433 - Mailbag
« Reply #4 on: March 02, 2013, 03:34:04 pm »
I bought the same weighing scale as Dave  :P
Seller says up to 3kg but it goes up to 10kg  :o

Does the zero shift after the 10kg?  If so the 10 kg is exceeding the elastic limit of the load cell. That would seriously affect the accuracy, Just trying to help  ;D

Offline SeanB

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Re: EEVblog #433 - Mailbag
« Reply #5 on: March 02, 2013, 03:40:04 pm »
I have no problems with massmeters, I can go from 1milligram to 150 kilograms, and they are both accurate and calibrated.  If it is rated 3kg and you put 10 on it it will be non linear for definite, and probably will have a permanent strain as well after the overload is removed. I took one out of service as it developed a non linear spot at the point where it was most often used. Fine at zero ( compensated for long term drift automatically) and was fine at 5kg, 15kg as well. 10kg was around 60g underreading, which put it out of the spec of 50g, and also out of the long term checks of it being within 5g of the nominal.
 

Offline T4P

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Re: EEVblog #433 - Mailbag
« Reply #6 on: April 27, 2013, 04:58:17 pm »
I bought the same weighing scale as Dave  :P
Seller says up to 3kg but it goes up to 10kg  :o

Does the zero shift after the 10kg?  If so the 10 kg is exceeding the elastic limit of the load cell. That would seriously affect the accuracy, Just trying to help  ;D
Hmm. I don't know what that means, lol
 

Offline robrenz

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Re: EEVblog #433 - Mailbag
« Reply #7 on: April 28, 2013, 01:44:30 am »
Hmm. I don't know what that means, lol

zero the scale
put 10kg on
remove the 10 kg
scale now reads something other than zero (several least significant digits or more)

This scenario would mean that the 10kg was enough to put a permanent set in the measurement flexure. (exceded the elastic limit of the flexure material) that is why it did not return to zero. 

Offline T4P

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Re: EEVblog #433 - Mailbag
« Reply #8 on: April 28, 2013, 10:06:19 am »
Hmm. I don't know what that means, lol

zero the scale
put 10kg on
remove the 10 kg
scale now reads something other than zero (several least significant digits or more)

This scenario would mean that the 10kg was enough to put a permanent set in the measurement flexure. (exceded the elastic limit of the flexure material) that is why it did not return to zero.
Ah, it doesn't do that.  ;D Just to be sure i put my entire rig on it and it went right back to zero kg
 


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