1502: Difference between revisions

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The first version used a CRT and is almost completely analog along with some descrete digital
The first version used a CRT and is almost completely analog along with some descrete digital
logic used to prefire and fire the tunnel diode pulser.  The later models (1502B/C) used an
logic used to prefire and fire the  
[[tunnel diodes|tunnel diode]] pulser.  The later models (1502B/C) used an
LCD display and a microprocessor.  The other major difference is the line charging method.
LCD display and a microprocessor.  The other major difference is the line charging method.
The 1502 uses a fast (36ps) tunnel diode pulser, the later models used a half sine wave to
The 1502 uses a fast (36ps) tunnel diode pulser, the later models used a half sine wave to
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sensitivity although it is much easier to destroy.
sensitivity although it is much easier to destroy.


There are four key parts in the 1502 that make repair difficult.  The origional sampling gate
There are four key parts in the 1502 that make repair difficult.  The origional sampling gate (CR1732, Tek 152-0631-00)  
(CR1732, tek 152-0631-00) is NLA, but Avago RF Schottky barrier diodes in the SOT series pair package
is no longer available,  
(Avago HSMS-2822, HSMS-282C) are a close substitute.  There is a snap-off diode (CR1632, tek 152-0335-01)
but Avago RF Schottky barrier diodes in the SOT series pair package
in the samping gate pulse shaper that is also NLA but it usually doesn't fail.  The first pulse shaping TD
(Avago HSMS-2822, HSMS-282C) are a close substitute.   
(CR1609, tek 152-0140-01, 10mA, 8pF) was a fairly common TD and there are Russian substitutes
There is a snap-off diode (CR1632, Tek 152-0335-01)
available.  The primary fast pulse TD (CR1703, tek 152-0489-00, 21mA, 1.5pF) is simply NLA.  Good Luck!
in the samping gate pulse shaper that is also  
no longer available but it usually doesn't fail.   
The first pulse shaping TD (CR1609, tek 152-0140-01, 10mA, 8pF) was a fairly common TD and there are Russian substitutes
available.  The primary fast pulse TD  
(CR1703, Tek [[152-0489-00]], 21mA, 1.5pF) is simply  
no longer available.  Good Luck!


If you want to design a replacement, I suggest looking at Analog Devices ADCMP580, and Starecki and Misiaszek's
If you want to design a replacement, I suggest looking at Analog Devices ADCMP580, and Starecki and Misiaszek's
paper "Low cost programmable pulse generator with very short rise/fall time".
paper "Low cost programmable pulse generator with very short rise/fall time".


There appears to have been an optional "static supressor" available, tek 011-0132-00, in a BNC M-F package used
There appears to have been an optional "static supressor" available, Tek 011-0132-00, in a BNC M-F package used
to protect the sampler and TD.  It's pretty obscure.
to protect the sampler and TD.  It's pretty obscure.


Revision as of 20:50, 19 February 2012

The Tektronix 1502 is a series of Time Domain Reflectometers commonly used to test coaxial cables athough they have many other uses. The US military was a major purchaser; most of the first series (the 1502, no letter) will be found surplus with some sort of US military property ID tag and an NSN sticker.

The first version used a CRT and is almost completely analog along with some descrete digital logic used to prefire and fire the tunnel diode pulser. The later models (1502B/C) used an LCD display and a microprocessor. The other major difference is the line charging method. The 1502 uses a fast (36ps) tunnel diode pulser, the later models used a half sine wave to charge the line. The TD pulser, with it's Dirac delta edge gives much better short range sensitivity although it is much easier to destroy.

There are four key parts in the 1502 that make repair difficult. The origional sampling gate (CR1732, Tek 152-0631-00) is no longer available, but Avago RF Schottky barrier diodes in the SOT series pair package (Avago HSMS-2822, HSMS-282C) are a close substitute. There is a snap-off diode (CR1632, Tek 152-0335-01) in the samping gate pulse shaper that is also no longer available but it usually doesn't fail. The first pulse shaping TD (CR1609, tek 152-0140-01, 10mA, 8pF) was a fairly common TD and there are Russian substitutes available. The primary fast pulse TD (CR1703, Tek 152-0489-00, 21mA, 1.5pF) is simply no longer available. Good Luck!

If you want to design a replacement, I suggest looking at Analog Devices ADCMP580, and Starecki and Misiaszek's paper "Low cost programmable pulse generator with very short rise/fall time".

There appears to have been an optional "static supressor" available, Tek 011-0132-00, in a BNC M-F package used to protect the sampler and TD. It's pretty obscure.

The other common failure is the battery. The power supply was designed to protect both the instrument and the battery from abuse, so any failure will cause the power supply to latch up (via Q6547/Q6549) and the unit will appear dead. The pack is rebuildable with NiCd battery cells. To operate without a battery in place use a 200 to 270 ohm 10W power resistor in parallel with a 2200uF cap (>25V); this will fool the power supply protection circuit into thinking that it's charging a valid battery.

Service Manuals:

Note that the manuals for the 1502B and 1503C are still available from Tektronix.

  • Top boards of the 1502

    Top boards of the 1502

  • Underside of 1502 with stripline sampler and pulser exposed

    Underside of 1502 with stripline sampler and pulser exposed

  • Sampling gate near the BNC end of stripline

    Sampling gate near the BNC end of stripline

  • Pulser end of the stripline

    Pulser end of the stripline

  • Pulser TD removed from stripline

    Pulser TD removed from stripline

  • Pulser TD curve traced with a 576

    Pulser TD curve traced with a 576

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