Huntron Tracker Model 30 - Relay Replacement Repair

[Josh In Seattle]

Huntron Tracker Model 30 - Relay Replacement Repair
I picked up a Tracker Model 30 setup on eBay, manufactured in 2012. Unit was functional but hadn't been aligned or verified since 2013. Here's a writeup of the diagnosis and repair for anyone else dealing with similar issues on these units.

Initial Assessment
Using Huntron workstation I did do a basic live functional test with the model 30, I did notice that on lower stimulus settings the graph was jumpy and fuzzy - it also had a tendency to jump out at 30° and 45° angles, upward, which I'm told is definitely a sign of an alignment issue. The Huntron Workstation application has Tracker 30 diagnostics that provide alignment (calibration) and verification functions. After first power-up I ran a verify against the ancient 2013 alignment data and got 305 failures across both channels, every voltage level, every impedance range. No surprise after 12+ years without service.

I ran alignment to establish fresh calibration values, then immediately verified again. Failures dropped from 305 down to 34. The alignment corrected all the age-related drift on both channels, but 34 failures stubbornly remained that no amount of re-alignment could fix. That told me something in the hardware was failing, not just drifted. These are the errors that remained:

Phase X Offset Verify Channel A 0.2V 50KOhms 1.7KHz Align 2072 Val 1973 Tol 96 Dif -99 FAILED***

Phase X Offset Verify Channel A 0.2V 50KOhms 2KHz Align 1986 Val 2085 Tol 96 Dif 99 FAILED***

Resistance Delta Verify Channel A 0.2V 100KOhms 20Hz Align -158 Val 32 Tol 128 Dif 190 FAILED***

Resistance Delta Verify Channel A 0.2V 100KOhms 40Hz Align -90 Val 54 Tol 128 Dif 144 FAILED***

Resistance Delta Verify Channel A 0.2V 100KOhms 80Hz Align 73 Val -104 Tol 128 Dif -177 FAILED***

Resistance Delta Verify Channel A 0.2V 100KOhms 90Hz Align -64 Val 79 Tol 128 Dif 143 FAILED***

Phase X Offset Verify Channel A 0.2V 100KOhms 140Hz Align 2100 Val 1974 Tol 96 Dif -126 FAILED***

Phase X Offset Verify Channel A 0.2V 100KOhms 150Hz Align 2114 Val 1944 Tol 96 Dif -170 FAILED***

Phase X Offset Verify Channel A 0.2V 100KOhms 190Hz Align 2124 Val 1939 Tol 96 Dif -185 FAILED***

Phase X Offset Verify Channel A 0.2V 100KOhms 200Hz Align 1954 Val 2128 Tol 96 Dif 174 FAILED***

Phase X Offset Verify Channel A 0.2V 100KOhms 1.3KHz Align 1943 Val 2079 Tol 96 Dif 136 FAILED***

Phase X Offset Verify Channel A 0.2V 100KOhms 1.4KHz Align 1943 Val 2147 Tol 96 Dif 204 FAILED***

Phase X Offset Verify Channel A 0.2V 100KOhms 1.5KHz Align 2037 Val 1880 Tol 96 Dif -157 FAILED***

Phase X Offset Verify Channel A 0.2V 100KOhms 1.6KHz Align 2163 Val 2021 Tol 96 Dif -142 FAILED***

Phase X Offset Verify Channel A 0.2V 100KOhms 3KHz Align 1943 Val 2119 Tol 96 Dif 176 FAILED***

Phase X Offset Verify Channel A 0.4V 100KOhms 600Hz Align 2104 Val 1967 Tol 96 Dif -137 FAILED***

Phase X Offset Verify Channel A 0.4V 100KOhms 700Hz Align 2108 Val 1999 Tol 96 Dif -109 FAILED***

Verification FAILED on Sunday, March 29, 2026 at 4:38:39 PM

I did try additional alignment and verification and the errors consistently reappeared, twice, so I knew this was a hardware failure at this point.

The Failure Pattern
Every single persistent failure shared the same fingerprint:

-   Channel A only. Channel B was clean across the board.
-   Concentrated at 0.2V with 50K and 100K ohm resistance ranges.
-   A handful at 0.4V / 100K ohms.
-   Almost all were "Phase X Offset" failures -- meaning the timing relationship between the drive signal and the measurement was shifting, not the amplitude.
-   The "difference values" alternated randomly between positive and negative, which rules out a steady drift and points to something intermittently unstable.

The severity scaled with signal level. At 200mV, 50K through 100K ohms, you're down around 2 microamps of test current -- the absolute minimum the instrument produces. At those levels, any parasitic resistance in the path gets amplified into a measurable error.

Root Cause: Relay Contact Degradation
Looking at the PCB, the resistance ranges are selected by a bank of signal relays. Each relay switches in a precision resistor that sets the current limiting for that range. You can see the resistor stencil labels right in front of each relay on the board:

-   **K39** selects the 50K ohm range via **R21** (49.9K)
-   **K40** selects the 100K ohm range via **R22** (100K)

These are the exact two ranges that were failing. The resistors themselves were fine -- the same resistors pass at higher voltages where there's more signal current to mask small contact resistance variations.

The problem was the relay contacts. After 12+ years and countless actuation cycles, the contacts likely developed micro-pitting and oxide film. This creates variable contact resistance. At high signal levels you'd never notice it. But at 0.2V through 100K ohms, a few ohms of variable series resistance interacts with the capacitances already present in the signal path to form an RC network with a constantly shifting time constant. That shows up as random phase jitter in the measurement -- exactly what the diagnostic was reporting.

Using some guessing and contact measurement, I additionally figured relays K44 through K47 also deserved attention. I believe one or more of these relays is involved in the self-test (loopback) or some kind of safety (cut-in/cut-out) behavior and likely their contacts are worn, so they're prime candidates for wear.

The Repair
Replaced all six relays with brand new, same-manufacturer, same-model (MS05-1A87-75D) parts, from Digikey.

I used polyimide (Kapton) tape around each relay site to protect the surrounding SMD components during desoldering. The old relays to be replaced are marked with silver Sharpie so they're easy to identify on the board. I used a generic, low melt, desoldering compound to flood all four contact pins of each relay. I used a 300W desoldering gun to keep the desoldering compound molten until the heat penetrated enough where the relay basically fell right out of the bottom of the board then I immediately vacuumed up the molten compound with the desoldering gun. Rinse and repeat for every relay. It's a little pricey but I tried to use as little of the low melt desoldering compound as I could. I believe it paid off.

The Cold Start Oddity
Here's where it gets interesting. After installing the new relays, I ran alignment and then verified 25 minutes later -- and got 33 failures (very similar , mostly all about Phase X Offset errors). Almost identical to the pre-repair count. Not exactly confidence-inspiring after a relay swap.

But then I ran alignment a second time and clicked verify immediately and got zero failures. Verified again 10 minutes later -- zero failures. Again 48 minutes later -- zero failures. Again at an hour and a half, zero failures.  A week later...zero failures.  So new alignment values were accepted by the diagnostic.

The pre-repair data showed the same pattern: first (ever) logged alignment produced 34 failures, second produced 18, then 0. But with the old worn contacts, it could never get to zero no matter how many times you cycled it. With new contacts, the second cycle clears completely and stays clean.

Bottom line: After any relay replacement, always run alignment twice or more before condemning anything. The first pass may act as a conditioning cycle.

Final Confirmation
After the repair, I left the unit powered off on the workbench for a full week. Came back April 18, powered it up, let it idle for an hour, and ran verification without re-aligning -- just checking whether the April 12 alignment data was still valid after a week of storage.

****Verification Successfully Complete. - Zero failures.****

The unit now passes 100% across all voltages, all resistance ranges, all frequencies, both channels. So I found that, signal relay contacts wear out, even while still functional and phase offset failures (as opposed to amplitude/resistance delta failures) point to variable impedance in the signal path. A worn relay contact can create exactly this -- variable series resistance that interacts with circuit capacitance to shift phase unpredictably.

I hope this helps anyone else working on a Model 30. These are excellent instruments and very much worth repairing!