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Apple Monitor II Capacitor Replacement Guide

From RetroTechCollection
Apple Monitor II (Ben Boldt, Wikimedia Commons, public domain)

Electrolytic capacitors on the main electronics assembly of the Apple Monitor II (A2M2010), which is also the board in the Apple Monochrome Monitor IIe (A2M6017).[1] The values below are read from Apple's own schematic, drawing 050-5020-A, Schematic, Main Electronics, Monitor II, Domestic, revision A.[2] Apple sold the board only as a complete exchange assembly (661-75134) and published no capacitor list.[3] Sams's parts list names only C420 among the electrolytics, because it lists only parts not normally stocked by distributors.[4]

The monitor has a CRT with an anode at about 13 kV. Discharge it before removing the board: see CRT Discharge Procedure and Apple Monitor II General Maintenance.

Electrolytic capacitors

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Capacitance in µF. The drawing is for the domestic (115 V) model; Sams's board number for the same assembly is 060-01-001, revisions B and C.[5]

Monitor II main electronics assembly, electrolytic capacitors (Apple drawing 050-5020-A)
Ref Capacitance (µF) Voltage Notes
C101 22 25 V At the video input
C102 220 25 V
C104 22 25 V
C108 220 25 V
C109 10 25 V
C110 470 25 V
C113 10 25 V
C203 100 25 V
C205 220 50 V
C209 1 50 V Named by Sams in the vertical checks
C303 100 25 V Named by Sams in the vertical checks
C307 10 25 V Named by Sams in the vertical checks
C308 1000 16 V Named by Sams in the vertical checks, with the yoke
C407 4.7 25 V
C411 4.7 25 V
C412 100 25 V
C416 100 25 V
C417 1000 16 V
C420 16 25 V Non-polarised (NP); Sams names it in the horizontal linearity checks
C501 10 160 V
C502 3.3 50 V
C601 3300 35 V Reservoir after the bridge rectifier D601-D604
C603 47 25 V At the regulator IC601

That is 23 polarised electrolytics and one non-polarised. The film and ceramic capacitors on the main board (for example C414 and C415, 0.033 µF 400 V) and on the line filter board (C701 0.47 µF, C702 0.01 µF, C703 and C704 4700 pF) are not electrolytics.[2] The notes column records where Sams's troubleshooting section names a part; Sams cites C209, C303, C307 and C308 for vertical faults and C414, C415 and C420 for horizontal linearity and foldover.[6]

The schematic print is a poor copy in places. Check each value against the marking on the part before ordering.

Procedure

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  1. Unplug the monitor, open the case and discharge the CRT. Leave an earth lead on the anode while you work.[7]
  2. Remove the main electronics assembly as Apple describes. Cut the glue under the right-rear corner with a knife before lifting the board, or the corner breaks.[8]
  3. Replace the capacitors one at a time, matching polarity to the board marking. Keep at least the original voltage rating. C420 must be a non-polarised (bipolar) type.
  4. Refit the board, reconnect the anode cap with both clips seated, and dress the wiring so the chassis tray slides freely.[8]
  5. Power up and check the rails Sams gives: 22.5 V at the cathode of D604 and 14.9 V at pin 3 of the regulator IC601, and 14.9 V at the collector of Q401.[6]
  6. Recheck the vertical and horizontal adjustments, which Apple expects to need touching up after board work. See Apple Monitor II General Maintenance#Adjustments.
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References

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  1. ↑ Apple Computer, Monitor II/Monochrome Monitor IIe Technical Procedures, 072-0229, note p. 0.0 (PDF p. 3). Hosted here: File:Apple Monitor II and Monochrome Monitor IIe Technical Procedures.pdf.
  2. ↑ 2.0 2.1 Apple Computer, drawing 050-5020-A, Schematic, Main Electronics, Monitor II, Domestic, revision A. Hosted here: File:Apple Monitor II Main Electronics Schematic 050-5020-A.pdf.
  3. ↑ Monitor II/Monochrome Monitor IIe Technical Procedures, Illustrated Parts List, p. IPL.3 (PDF p. 83).
  4. ↑ Howard W. Sams & Co., ComputerFacts CMT9-1, Apple Monitor II Model A2M2010, April 1986, parts list, p. 15 (PDF p. 9). Hosted here: File:Sams ComputerFacts CMT9 Apple Monitor II A2M2010.pdf.
  5. ↑ Howard W. Sams & Co., ComputerFacts CMT9-1, GridTrace location guide, p. 12, and semiconductor parts list notes, p. 14 (PDF pp. 6, 9).
  6. ↑ 6.0 6.1 Howard W. Sams & Co., ComputerFacts CMT9-1, Troubleshooting, p. 17 (PDF p. 6).
  7. ↑ Monitor II/Monochrome Monitor IIe Technical Procedures, Take-Apart, Discharging the CRT, pp. 2.4-2.5 (PDF pp. 14-15).
  8. ↑ 8.0 8.1 Monitor II/Monochrome Monitor IIe Technical Procedures, Take-Apart, Main Electronics Assembly, pp. 2.12-2.17 (PDF pp. 22-27).


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