547/Repairs

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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.

David Wise's 547 Repair History

MY TEKTRONIX 547 OSCILLOSCOPE REPAIRS
January 2021
David Wise

S/N 4369

Acquired around 2000 from Bob in South Bend WA
Came with 1A4, 1A5, 1A7 #257

Had lossy epoxy HV transformer which failed. Rewound by Bill Schell. (Chuck Harris says Bill did layer wind on a spindle with #32 instead of universal wind with #38 like Tek, but mine looks like universal.) I still have 5642's, and the filament loops fit easily.

MODS APPLIED

Around 2000

M11722 (5680) Time Base 'A' Unblanking Circuit Resistor Added To Assure 'B' Trace Is Brighter Than 'A' Trace At Some Sweep Speeds

  • Add R377 1K, see manual page 163 'A' Sweep Generator
  • I also put a cap across it like Tek should have

M11808 (5680) Horizontal Amplifier RC Network Added To Protect CRT Phosphor From Possible 'Turn-On-Flash' Burns

  • Cap yanks beam to side during power on
  • Add D561, C562, R562

M11809 (S/N 5830) to limit 6AU5 screen voltage to +125V.

  • Add D803, D804, R804

M12258 (S/N 6380) my field version: teepee a regular diode in series with D693 to prevent forward bias.

PARTIAL M14194 (S/N 10730) Vertical Amplifier Components Changed to Improve 1-15kHz Frequency Response

  • They shortened the existing time constants and added a new long time constant
  • Part of the mod changes R1077 from 16K fixed to 30K variable.
  • I hand-selected a fixed resistor (24K) shunted across original R1077.
  • Did not do other parts:
    • Change C1077 value
    • Change R1126 value
    • Add R1091/C1091

M14860 (S/N 11270) Vertical Amplifier Diodes Added To Protect +100V Supply

  • Add D1114 in series with D1109

December 2017

SYMPTOM 201712: B Trigger: Auto works when Level is cranked one way but not the other. Effect reverses when you flip the Slope switch.
CAUSE: D45 (B Trigger tunnel diode) Ip decreased from 10mA nominal to 6mA.
I think that a turn-off transient from the Auto multivibrator was retriggering D45 which in turn retriggered the Auto multi and inhibited bright-line Auto.
ACTION: Original part is 152-0154 i.e. TD253, which is Germanium. I replaced it with a GaAs Russian surplus 3I306L.
FIXED. Seems fine even though the TD is slower(?) and has higher Vv and Vf.

SYMPTOM 2021: HV transformer runaway!
ACTION: Bake in instrument
FIXED. Moisture ingress due to long sit in cold humid basement?

SYMPTOM 20220520: Jitter in fast B sweep, triggering not as good as A
I figure it's that Russian tunnel diode and I didn't notice before
WILL NOT FIX

SYMPTOM 20220520: Poor vertical HF response: -3dB at 35MHz not 50MHz; 10ns risetime
CONTEXT: Using 8640B for f, 067-0521-01 for t
ACTIONS:

  • Re-seat transistors, no effect
  • Re-seat plugin, some effect
  • Adjust per Table 5-8, some effect

NOTE: L1157 has no effect, always slight wrinkles always in same spots
NOTE: C1029 subtle effect but canceling bump also increases risetime slightly
ACTION: Accidentally leaned on the delay line, DRASTIC EFFECT, flexed it, more effect.

  • Flexed it more, no further effect.
  • Now significant rolloff probably due to previous adjustment attempt.
  • But now able to flatten by adjusting Table 5-8 R's and C's.

FIXED. 7ns risetime, 45MHz
WHAT DID I DO?
WATCH delay line, is it sick?

SYMPTOM 20220520: Crumbling carry handle
NOTE: Crumbling handles are on a 535A rail, probably 381-0204-00 (blue leatherette)
I thought I had new ones but where are they?
ACTION: Bought complete 381-0217-00 top rail with vinyl handles 367-0037-00 from eBay seller
NOTE: 6" grip with captive square rings
NOTE: Earlier 535A rails are 381-0121-00 (black leather) and 381-0149-00 (blue leather)
NOTE: 547 handle also used on late 503

SYMPTOM 20220526: Flickering trace first few minutes after cold power-on
CANNOT REPRODUCE 20220528
HV Test Point

  • -1900V on Fluke 825A with Fluke 80K-40 (1000Meg), raster
  • -1898V on 067-0543-99 (100Meg), beam off

INTENSITY string

  • -2015V on 067-0543-99, beam off

TODO:
M14928 (S/N 12110) Swap D672A-D for stronger, 1N4004/1N5060/1N5404.
M15145 (11890) Resistor Changed To Ensure Operation Of Vertical Position Neon

  • R1187 was 330K CC now 301K 1%. I will simply select a carbon film part.

M12876 (6300) Motor Base Changed To Improve Ground Connection

  • Just make sure we have a solid equipment ground

MAYBE:
M11122 (S/N 4750) Vertical Amplifier Gain Potentiometer Range Increased
M11707 (S/N 5680) Vertical Amplifier Output Transistors Changed To Reduce Failures

  • Look for 153-0548-00

M12460 (S/N 6730) Vertical Amplifier Input Tube And DC Balance Potentiometer Replaced To Improve Vertical Amplifier Balance
M14194 (S/N 10730) Vertical Amplifier Components Changed To Improve 1-15kHz Frequency Response
M13839 (8420) 'B' Sweep Chassis Wire Modification Incorporated To Eliminate Sweep Free-Running

  • Wire strap to Q44.C relocated, and C44/C45 leads shortened

WILL NOT DO:
M12027 (6740) 040-0549-00 Trigger Circuits Rewired To Improve Stability
M14339/M15344 050-0479-01 Disconnect Diode Replacement

  • 1972
  • There's a mystery here. New Q286 is 151-0277-00. Manual says RCA 38520 and there's NO info on the web.
  • Common Design 1982 says 151-0277-00 is 2N3933 830MHz TO-72 Do Not Use.
  • NJSemi 2N3933 datasheet says 0.55pF, VHF/UHF amplifier.
  • 7L5 military manual TM11-6625-2759-14&P says 151-0230-00 is RCA 38520 but Common Design says it's 2SC1260 1GHz 0.7pF
  • New D286 152-0185-00 "replaceable by 1N4152"
  • Common Design says Do Not Use, use 151-0141-02
  • New D291 is 152-0165-00, Common Design says 1N3579, 10pA at 3V, no info on web.
  • 556 Lecture Notes says it's a selected 1N3579.
  • D291 protects D286 from excessive reverse voltage
  • D90 (same as D291) added S/N 3130 M10510 "to protect disconnect diode".
  • D86/D286 were originally Tek-made GaAs and needed protection.
  • RA1092, no info except small-signal diode
  • Made by Microsemi and Freescale. It seems to me that maybe a 1N4152 doesn't need protection.

M12463 (11890) Tunnel Diodes Replaced To Increase Power Rating

  • D45/D245 was 152-0154-00 now 152-0140-01
  • D45 already replaced with Russian 3I306L

M13384 (7960) Sweep Trigger Generator Amplifier Tubes Changed To Checked/Aged/Balanced Tubes
050-0479-01 (12480) Disconnect Diode Replacement
M11266 (5310) [timing caps drift due to temperature cycling]
M11517 (5480) [timing resistors]
M13653 (8290) [timing resistors]
M14095 (10260) [timing resistors]
050-0473-00 (12471) Sweep Steering Diodes
M11212 (5130) [mag gain resistor]
M12856 (10200) [calibrator resistors]
M12130 (6730) [anti-slip feet]
M11191 (8630) [standardize zener part numbers]
M15322 (12800) [cabinet latches]

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