Difference between revisions of "THS720"

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(pictures)
(attenuator and analog scope section)
Line 15: Line 15:
  
 
Recommended probes are the [[P5102]] and the [[P6113B]], both are 10X probes
 
Recommended probes are the [[P5102]] and the [[P6113B]], both are 10X probes
with protected grounds for isolated measurements.  
+
with protected grounds for isolated measurements.  The [[P5102]] has the best
 +
isolation, allowing 600V between reference ground and earth ground.
  
 
==Internals==
 
==Internals==
  
 
Primary microprocessor is the Motorola/Freescale MC68331CFC16.  There is also
 
Primary microprocessor is the Motorola/Freescale MC68331CFC16.  There is also
an Intel flash E28F008SA120 for setup, cal and waveform storage.
+
an Intel flash E28F008SA120 for setup, cal and waveform storage.  The switching power
 +
supply is run by a TL1451A, a TI two channel boost/buck controller.  The DMM is
 +
a 3.5 digit Maxim MAX134CQH.
 +
 
 +
The analog scope section starts with an attenuator hybrid driven by 4 channels of
 +
HP (now Avago) optoisolators and NEC relays.  The hybrid contains the AC coupling
 +
capacitor and many laser trimmed resistors along with a custom Tek [[165-2545-00]] BGA.
 +
The signal then passes through a single-ended to differential transformer and
 +
goes to a custom labeled Maxim 2 channel high speed A/D converter [[234-1503-20]].
 +
Note that the differential signal layout for channel 2 is not as good as channel 1
 +
since one side of channel 2 goes through 2 vias not found on channel 1.
  
 
==Repair Issues==
 
==Repair Issues==
Line 26: Line 37:
 
The service manual shows how to remove the calibration protection jumper.
 
The service manual shows how to remove the calibration protection jumper.
 
The DMM calibration step requires a good calibrator capable of doing 850 VDC,
 
The DMM calibration step requires a good calibrator capable of doing 850 VDC,
and 600 VAC at 500 Hz.
+
and 600 VAC at 500 Hz.  Scope calibration is much simpler requiring only a
 +
square wave pulser and a DC voltage source.  Note that after a cal fail, there
 +
is an error log in a nearby menu indexed by power on count.
 +
 
 +
The battery pack is, of course, custom.  It appears to be 4 C cell NiCd pack
 +
with the positive terminal moved to a ring around the bottom (most negative) cell.
 +
If you are not concerned with interchanging packs or using the separate charger, the
 +
cells can simply be soldered into the lower housing.
  
See [[THS700]].
+
See [[THS700]] for the manuals.
  
 
==Pictures==
 
==Pictures==
Line 37: Line 55:
 
File:ths720std-powerbnc.JPG|THS720 std main board BNC inputs and power supply
 
File:ths720std-powerbnc.JPG|THS720 std main board BNC inputs and power supply
 
File:ths720std-backpcb.jpg|THS720 std back of main PCB
 
File:ths720std-backpcb.jpg|THS720 std back of main PCB
 +
File:ths720std-attenuator.JPG|THS720 std attenuator with cover removed
 +
File:ths720std-scopeanalog.JPG|THS720 std analog scope section
 
</gallery>
 
</gallery>
  
 
[[Category:THS series scopes]]
 
[[Category:THS series scopes]]

Revision as of 23:48, 21 October 2014

Tektronix THS720 Std probe compensation

The Tektronix THS720 is a portable 100 MHz bandwidth 500 MS/s (each channel) two channel digital oscilloscope. There were two variants, the THS720 STD and the THS720A. The primary difference is that the THS720A will trigger from the DMM input.

Operation

Due to the isolated inputs, the probe ground must be connected even when compensating the probes with the "PROBE COMP" output. It can be used with any BNC probe but the scale factor pin found on many Tektronix probes is not used. The vertical menu has a scale factor entry (1X, 10X, 100X, 1000X) which can also be used for direct BNC inputs.

Recommended probes are the P5102 and the P6113B, both are 10X probes with protected grounds for isolated measurements. The P5102 has the best isolation, allowing 600V between reference ground and earth ground.

Internals

Primary microprocessor is the Motorola/Freescale MC68331CFC16. There is also an Intel flash E28F008SA120 for setup, cal and waveform storage. The switching power supply is run by a TL1451A, a TI two channel boost/buck controller. The DMM is a 3.5 digit Maxim MAX134CQH.

The analog scope section starts with an attenuator hybrid driven by 4 channels of HP (now Avago) optoisolators and NEC relays. The hybrid contains the AC coupling capacitor and many laser trimmed resistors along with a custom Tek 165-2545-00 BGA. The signal then passes through a single-ended to differential transformer and goes to a custom labeled Maxim 2 channel high speed A/D converter 234-1503-20. Note that the differential signal layout for channel 2 is not as good as channel 1 since one side of channel 2 goes through 2 vias not found on channel 1.

Repair Issues

The service manual shows how to remove the calibration protection jumper. The DMM calibration step requires a good calibrator capable of doing 850 VDC, and 600 VAC at 500 Hz. Scope calibration is much simpler requiring only a square wave pulser and a DC voltage source. Note that after a cal fail, there is an error log in a nearby menu indexed by power on count.

The battery pack is, of course, custom. It appears to be 4 C cell NiCd pack with the positive terminal moved to a ring around the bottom (most negative) cell. If you are not concerned with interchanging packs or using the separate charger, the cells can simply be soldered into the lower housing.

See THS700 for the manuals.

Pictures