Symptom:? I have a Textronix TDS 460A Digital O Scope that worked fine at last use.? Unit was unused for about 4 ¨C 6 months.? Upon power up the CRT screen lights up and the ¡°clock¡± emoji is present on the screen.? The front panel lights flash and you can hear the relays cycling.? The fan runs.? After about 10 seconds the unit goes into a cycling state, cycling on and off every two or three seconds.? Each time it powers the fan runs and the panel lights flash.? You can hear a ticking sound that seems to decrease in volume as time passes.
Question:? The troubleshooting procedures decision points ask, ¡°Does the oscilloscope power up.¡±? Does the fact the unit powers up for 2 seconds repeatedly constitute ¡°power up¡±.? If it does You move beyond the Backplane board.? If it does not, you are looking at either a LVPS A25, Front Panel A06, Backplane A01, or Aux Power Board A07 failure/replacement.
Troubleshooting:
1.????? Checked the voltage of the two 3V batteries.
a.????? Battery to A03 CPU Assy. Read 2.04V
b.????? Battery to A09 DSP Assy. Read 3.0V
c.????? Reversed batteries on reinstallation.? No change in symptoms.
2.????? Verified 115V AC at pins 1 & 3 of J! on LVPS.? (Aux Pwr board to LVPS)
3.????? Performed the LVPS troubling shooting procedure (Fig 6-31 pp 6-78)
a.????? Checked voltages (Table 6-11, pp 6-79)
b.????? All well below spec. in millivolts..
c.????? Coming down left side all answers are ¡°yes¡± except last question (Are secondary voltages within Spec (Table 6-11, pp 6-79).
d.????? Procedure would indicate that the issue is not with the A25 LVPS.
4.????? Disconnected white wire between Aux. Pwr. Board and LVPS Board.
a.????? No change in performance or symptoms. Remade connection.
5.????? Disconnected plug from J2 (22 pin connector on A25 LVPS board).
a.????? No change in performance or symptoms.? Remade connection.
6.????? Pulled the LVPS board from scope.
a.????? No obvious problem.? No corrosion, no swollen E caps, no burn sites.
b.????? Checked E caps in circuit with a MESR meter.? Seemed ok.
c.????? Read something about R410 (1M).? Read it while in circuit and it appeared to be open.? Planning on removing one side from circuit and read again.
7.????? Performed the Backplane trouble shooting procedure (Fig. 6-46 pp 6-92)
a.????? Again, the question goes to what constitutes ¡°power up.¡±
????????????????????????????????????????????????????????????? i.????? If ¡°yes¡± could be issue is elsewhere.
???????????????????????????????????????????????????????????? ii.????? If ¡°no¡± could be problem with A25 LVPS, A06 Front Panel, A01 Backplane, or A07 Aux. Pwr. Board.
8.????? Pulled A03 CPU, A02 Display Assy., and A09 DSP Assy.
a.????? No obvious problem.? No corrosion, no swollen E caps, no burn sites.
b.????? Reinstalled all three.
9.????? Visually inspected A01 Backplane board while Ao3, A02 and A07 out
a.????? No obvious problem.? No corrosion, no swollen E caps, no burn sites.
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I'd appreciate any advice, insight, and ideas on where to go from here.? For info, you are talking to a mechanical guy.? If it had oil or water leaking out or made a grinding noise I could figure it out.
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Thanks, 73 Harrison N1FAM
Cubdriver