547/Repairs

Power supply Electrolytic Capacitors

Depending on the age of the instrument, the main electrolytic capacitors may be dry or leaky. You may want to test and replace or reform them (if you believe in doing so).

There is no slow power up option here as the plate voltage for all the tubes are controlled by a time delay relay

You can remove the time delay tube and power up the instrument with just heater supply to tubes.

2N2207 Tin Whisker

2N2207 used in various sections can fail due to Tin whisker. Easy way to identify is by tracking the AC signal as per schematic and spot the offending transistor, where the signal will disappear.

Tunnel Diode

547 uses tunnel diodes in the Timebase for generating trigger and delayed trigger. They can also fail. Tunnel diodes are sensitive, be careful while soldering them and use proper heat sinking to avoid damage to the Tunnel diodes. A failed tunnel in the trigger will result in sweep free running in auto mode and unable to lock. Normal mode sweep will not trigger.

HV Transformer

Refer to 547 Main page for details.

General Troubleshooting

Refer to service manual first for the overview of the equipment and general troubleshooting procedure with specific component level troubleshooting chart.

If you are new to the instrument, ensure that the scope is in the right settings. For example, trigger (in Auto), V and H positions, focus/intensity at the at correct levels and Time base selector switch is selected for right time base.

At a high level the process is to start with power supplies, and are ensure all power supply voltages are within the specified tolerance. There are a dedicated power supply test point ceramic strip on the chassis. Refer service manual.

1. Isolate the problem to a specific section first, for example Power supply, HV, Vertical, Horizontal, Trigger.
2. There are DC voltages marked in every section of the schematic. Set the oscilloscope to the specific settings as mentioned in the service manual and verify all DC bias voltages at the schematic section in question are matching service manual. Once again remember to keep the scope in the specific settings as specified in the service manual. The failing section of the schematic can be easily spotted by a missing or incorrect DC bias value, mostly due to shorted or open components.
3. There are AC waveforms shown in the schematic for every block of the schematic. Verify and confirm the same with another scope to isolate the failing component/section.
4. Service manual explains the schematic in detail, refer it for a detailed understanding of the section you are troubleshooting.
5. You can inject external H-signal to isolate sweep generator and H- AMP section. Set the scope to external H input and apply external H signal to verify the H-Amp is working. This will help you narrow down the problem between H-Amp and Sweep/Time Base.