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HP 70001A Power Supply Refresh

Posted on November 17th, by Shaun Merrigan in Electronics, Test Equipment, Troubleshooting. Comments Off on HP 70001A Power Supply Refresh

I have recently begun to restore several pieces of Hewlett Packard 70000 Series MMS (Modular Measurement System) equipment. The basic component of the system is a power and/or display frame which can house various test equipment modules. This post documents my restoration of the HP 70001A Power Supply.

The Hewlett Packard 70000 MMS is a high-performance, modular measurement system for RF, microwave, and Lightwave measurements. The MMS instruments include spectrum analyzers, signal generators, power meters, DMM, digital oscilloscope, counter, and more. The system is assembled by inserting the appropriate modules into a mainframe (which supplies power, cooling, and communication) along with a display.

Historically, the 70000 MMS system was introduced in 1986 and continued to be available through at least 2001 (based on HP/Agilent catalogs). The latest prices (1993) I could find for a couple of representative HP 70000 systems follows (all USD):

  • HP 71100C 100Hz-2.9GHz Spectrum Analyzer System $49,000 (1993)
  • HP 71200C 50KHz-22GHz Spectrum Analyzer System $55,400 (1993)

The 1993 dollars convert to 2023 dollars of $106,000 and $120,000, respectively. Read more about the HP 70000 MMS system here.

As this mainframe has a low serial number, it was one of the earliest units produced. This is confirmed by component date codes of 1985/86. Also, this mainframe power supply board used the older axial lead filter capacitors where newer boards used snap in radial capacitors.

HP 70001A Mainframe Overview
HP 70001A Mainframe Overview
70001A PS Board New Type 1999
70001A PS Board New Type 1999. Note the snap-in filter capacitors.
HP 70001A PS Board As Received Overview
HP 70001A PS Board Older Style (1986). Note the axial lead filter capacitors (blue cylinders, top center).

When I inspected the board, I found several problems that required repair:

  • 37-year-old electrolytic capacitors all rated at 85o C
  • Power switch wired to be always on
  • 11 RIFA brand safety capacitors (X and Y rated) all with visible cracks in the epoxy case
  • One missed factory solder joint which left a transformer shield unsoldered

The most alarming finding was the badly deteriorated RIFA safety capacitors. Here are several examples:

HP 70001A Power Supply Board As Received Closeup
HP 70001A Power Supply Board showing original RIFA safety capacitors
RIFA Capacitor Crack Macro
RIFA Capacitor crack macro. Read more about these RIFA capacitors here.
HP 70001A Power Supply Board As Received Closeup
HP 70001A Power Supply Board showing original RIFA safety capacitors
HP 70001A Power Supply Board As Received Closeup
HP 70001A Power Supply Board as received closeup showing unsoldered connection from manufacturing
HP 70001A Capacitors Replaced
HP 70001A Capacitors Replaced

I have documented instances and examples of deteriorated RIFA safety capacitors before (read more here). This power supply board had eleven failing RIFA safety capacitors.

Based on the visual inspection and the history of the unit (thousands of hours), I completed the following:

  • Replaced all electrolytic capacitors with 105o C, long life, low ripple Nichicon or Chemi-Con types
  • Replaced all the cracked RIFA safety capacitors with new RIFA (now Kemet), Kemet or Panasonic film safety capacitors
  • Removed the jumpers across the power switch; clean and check the switch for proper operation
  • Re-soldered the factory missed solder joint
  • Cleaned and vacuumed the pcb and chassis
  • Checked the output voltages and ripple as per the service information
HP 70001A PS Board Refurbished Overview

All output voltages were within specification at 8.061 Vdc (40 kHz sine wave adj) and 5.127 Vdc with <5mV of ripple. The PS board was put back into the mainframe, and the mainframe was tested with a couple of 70k modules. The mainframe is working properly and will last another 35 years.

Next up will be servicing a couple of 70900A Spectrum Analyzer modules. Thanks for reading.

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