Tektronix TAP1500 probe repair

Feature set of this probe:

  • DC to >1.5 GHz Bandwidth
  • Risetime <267 ps
  • ± 8 Volts Dynamic Range with ±10 V offset capability
  • 1 MΩ Input Resistance
  • <1 pF Input Capacitance
  • 10x Attenuation
  • TekVPI Interface

I’ve bought this probe as broken/for parts. MSRP for the new Tek TAP1500 is around $3490 USD.

Diagnostics

Probe had no physical damage from outside, did not have any accessory bundled with sale. After connecting to Tektronix DPO7104 scope probe was correctly recognized and detected, however did not show any signal.

Teardown

Probe has all auxilary electronics in connector head, that plugs into TekVPI oscilloscope port. There are two 4-layer PCBAs, mounted with two mu-metal shields. Shields on photos below are already removed for clarity.

High-frequency analog signal directly passed to probe’s output BNC male port, without any connection on the PCBA. PCBA have “smarts” for probe detection/control and power supplies for active amplifier in the probe head.

Typical to Tektronix probes, there is little ATMEL ATmega8 8-bit microcontroller to select various probe functions, provide digital identification for scope, store serial number, etc.

Board have local power regulators to convert input +12V Bulk from scope into auxilary rails used by probe electronics. These are LM317MG in DPAK and Linear LT1616 switch-mode supply for +/-15V. There is also TI OPA237 op-amp in SOT23-5 package.

Onboard hardware handle programmable DC offset vernier function. It is implemented around BB DAC7612U which is dual-channel 12-bit fast voltage DAC. There are two dual ultra-low bias current high gain TI LMC6022 amplifiers

Common issue with this construction probe is damage of the probe tip. There is spring-loaded contact between alumina high-frequency active probe hybrid assembly and tip metal nose. If plastic cracked or damaged, precisely aligned contact will be lost and probe will cease to operate. Proper small spring contact installed in place will restore probe operation to normal.

Author: Illya Tsemenko
Published: April 13, 2020, 4:26 a.m.
Modified: April 13, 2020, 4:41 a.m.

References

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