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Tektronix THS7xxx Scope Hack/Teardown/Discussion - FW 1.16 found

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Zucca:
Hello,

PC SW to manage the Scope and take screenshots

Thanks to mrprecision

https://www.eevblog.com/forum/testgear/tek-ths720a-portable-scope-teardowndiscussion/msg3566625/#msg3566625

Video on how to install LED backlight

Thanks to mrprecision

In german language:
https://www.eevblog.com/forum/testgear/tek-ths720a-portable-scope-teardowndiscussion/msg3590917/#msg3590917

FW UPDATE

Thanks to superman13

https://www.eevblog.com/forum/testgear/tek-ths720a-portable-scope-teardowndiscussion/msg1480909/#msg1480909

Thanks to yaromka, here the FW1.16

FW 1.16

HACK

Thanks to TurboTom

https://www.eevblog.com/forum/testgear/tek-ths720a-portable-scope-teardowndiscussion/msg1073777/#msg1073777

SCHEMATICS

Thanks to R_G_B_

https://www.eevblog.com/forum/testgear/tektronix-ths700-tekscope-component-level-information-package-and-schematic/

ORIGINAL POST ON THS720A

I just got a Tek THS720A on Ebay. I like this device a lot, there is isolation everywhere: each scope CH and also the DMM input are isolated from each other. For a portable scope a good isolation is a must. The price range is much affordable than a Fluke scope which cost an arm and a leg.

It is a 100Mhz scope 2 CH, see some specifications here:


--- Quote ---Oscilloscope
Bandwidth    100-MHz Digital Real Time    
Sample Rate    500 MS/s each channel
Time/Division Range    5 ns to 50 s/div
Channels    Two
Sensitivity    5 mV to 50 mV/div (to 500 V/div with 10X probe)
Vertical Resolution    8 bits
Record Length    2500 points
Time Bases    Main or delayed run after
Display Modes    Vectors, dots, vector accumulate, dot accumulate, YT, XY
Triggering    Main only, edge, pulse, video lines, video fields
Acquisition Modes    Sample, envelope, average, peak detect
Autorange    Controls volts/div, time/div, trig level and acquisition mode
Waveform Maths    Ch1 + Ch2, Ch1 - Ch2, CH1 x Ch2
Cursors     H bars, V bars, paired (volts @ time)
Measurements    Pk-Pk, mean, min, max, rms, +width, -width, frequency, period, +duty, -duty, rise, fall

Multimeter
Resolution    4000 counts, 3.75 digits
DC Volts    400 mV-880 V True RMS
AC Volts    400 mV-640 V True RMS
Resistance    400-40 MW (with continuity beeper)
Diode Test    Up to 2 V
Other DMM Features    Autorange, true rms, average meas., hold, statistics, Min/Max Alarm

General Features
NV Storage    10 waveforms, 10 setups, 100 DMM saved screens
User Interface    Simplified TDS 320 with pop-up menus
I/O    RS-232 (to 38.4K baud)
Chassis    Battery Operated, hand-held
Reliability    Calculated MTBF 20,000 hours @ 25 degrees Celsius

--- End quote ---

The device needs 502mA (400mA when the LCD back light is off) from the 12VDC jack with no battery connected. In standby the current goes down to 8.45mA. With 5.5VDC on the 12VDC Jack the device was still on, but I did not went below that limit because I heard some funky noises (surely some switching DC/DC converter was screaming on me).

Regarding the battery, it is a 4.8V Ni-Cd (4xSize C) 2.8Ah. At 4.8V Battery voltage the device is asking 1.2A (1A when the back light LCD is off) to stay on. "Low Battery" warning appears at 4.6V. The power cuts off at 4.2V. In standby the current is about 176µA.
I performed a full discharge and then I charged it for 16 hours at C/10 280mA. Afterwards I did discharge test @1.2A CC:


 
not bad, 2.71 Ah Capacity and simulated 2:14 Lifetime to reach 4.2V (power cuts off).

The battery charger works like this (according to my reverse engineering):

VBatt <3.5V: CC charge at 110mA
VBatt >3.8V: charge current [mA]= -187.27*VBatt[V]+1283.63
3.5V<VBatt <3.8V: Previous state

Unfortunately It has a problem, see here for details
https://www.eevblog.com/forum/repair/tek-ths720a-thinks-there-are-110v-on-the-input-but-there-is-just-a-50-ohm-r/msg490731/
so I decided to tear it down. I hope I can fix it.

Here we go:

Under the front panel, solid metal panel for EMI with on top the the flex keyboard


below we can find the inverter board for the back light and the LCD


inverter top side


inverter bottom side


Nice touch, very practical to remove the rear battery case


without the inverter and the LCD


rear panel with battery holder


Battery contacts, in this way you can´t use regular 4 Size C batteries


main board bottom side; clearly CH 1, CH 2 and DMM are isolated


CH 1 circuit bottom side


DMM input bottom side


central digital stuff, bottom side


LCD output and power supply circuit, bottom side


Main board top side, funny those two transformer for each channel


Power supply, top side


CH circuits, I don´t want to desolder the cans yet


Interesting DMM input, extra PCB piece above the main board for EMI?


Main processor stuff, top side. Debug/Service port on the top?


Todo List:

1) Fix the offset Problem in CH1
2) Upgrade FW from 1.14 to 1.16, any advice? Looks like the FW is in U1 (from Memory_Erasure_071181500.pdf):


--- Quote ---156--7404--01

U1

IC, MEMORY; CMOS, FLASH ;1MEG X 8, 5.0
VOLT--ONLY, SECTOR ERASE;
AM29F080--120EC , 40PIN TSOPT&R

Flash memory which contains instrument
firmware, current setup, saved setups, saved
waveforms, saved data, waveforms, and
calibration constants.

--- End quote ---

3) Calibration


Possible Mods:

Does anybody has the schematics?

1) Build a switch to manage the back light LCD (turn off and on the inverter board). If there is enough ambient light, there is no need to use that energy. Why Tektronix did not built a back light switch?

2) Reverse Engineering the power supply and and battery charge circuit. Upgrade to Li ion by using three of those ones:
http://www.battery-matrix.com/3-2V26650-3300mah-LIFEPO4-IFR26650-3300mah.html
which just fit perfectly in the 4xSize C battery compartment. Target is to achieve a battery life between 2x and 3x than the current one.

3) Develop a 4 leds battery gauge.

------

High resolution pictures here:

http://postimg.org/gallery/6dfgsp1i/

Sorry I did everything with an IPhone 5, a Canon 60D will be in my hands soon.

BravoV:
Congratulation on the score and nice tear down.  :-+

Glad I can see the inner gut of this scope cause all this time I was curious how it looks like inside, thank you !  :clap:

Too bad, sorry to hear it has problem, mine doesn't have that. Also does it came with the P6117 probes ? These P6117 probes are designed and built specifically for isolated probing, and its hard to find and quite expensive even its used.  :'(

Btw, I made a discussion thread when I bought my THS710A -> HERE while ago.

About the NiCd battery pack, since the original Tek's batt pack is stupidly expensive  >:(, I modded 3 pieces of AA->C adapter, and made the battery pack for it, and used Eneloop Pro 2450 mAH batteries. It performs a lot better than that shitty NiCd cells, cause these NiCd is well known to have a really high self drain, mine will be fully discharged when left unused just for less than 2 weeks.  :--

Too bad currently I don't have the modded battery pack with me, but it looks very similar to Jay's one at above pointed THS710A discussion thread, but with slightly modded with a long cut across the battery pack to allow the AA batteries to be released as the adapters have hinges. Its very handy as I can charge each of them properly in externally NiMH charger Maha MH-C9000. Also the standard slow charging method at the scope is using low current & overnight method which is not suitable for NiMh cells. Attached below photo shows my other spare AA to C adapters that I planned to build another battery pack for my THS710A soon.

Zucca:

--- Quote from: BravoV on August 11, 2014, 02:59:33 am ---Also does it came with the P6117 probes ? These P6117 probes are designed and built specifically for isolated probing, and its hard to find and quite expensive even its used.  :'(

Btw, I made a discussion thread when I bought my THS710A -> HERE while ago.

--- End quote ---

Very nice thread! Thx!

One P6117 was there, and I already got a P5102 65$, eBay auction: #111429274915, as a second probe. Yes I am stupid I should had wait to see if my unit can be fixed or not.

Regarding the Battery, your solution is very reasonable. Still I would like to investigate the possibility to fit a Li ion with a properly charge system (inside the unit or outside through the 12VDC).

marshallh:
Regarding the firmware if I still had my ths720a I would dump it for you. However it may be possible to upgrade with a PC serial port connection app. You'll have a build a cable first and run the software in a VM

Zucca:
Thank you marshallh, it would be fantastic. I would love to get my hands on the 1.16 FW (according to my investigation this is the latest released FW by Tektronix) and surely a lot of people out there will love that.


--- Quote from: marshallh on August 11, 2014, 04:21:46 am ---However it may be possible to upgrade with a PC serial port connection app. You'll have a build a cable first and run the software in a VM

--- End quote ---

I have the RJ-45 to Sub-D9 RS232 cable, I mean this one:
http://www.tek.com/support/faqs/what-pin-out-ths700-rj45-connector-rs232

What app are is the one you are talking about? I searched in the www but no hope to find anything related to your suggestion. Is a VM a Linux Virtual Machine? If yes I have a FreeBSD box which should do the job.

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