Editing Atari 1050 Capacitor Replacement Guide

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[[File:Atari 1050 main board.jpg|thumb|right|350px|Atari 1050 main board; the large power supply filter capacitors are on the right]]
The '''[[Atari 1050]]''' has twelve aluminium electrolytic capacitors on its main board. Three are large filter capacitors in the power supply, which rectifies the adaptor's 9 V AC on the board itself; the others decouple the regulated rails and sit in the spindle motor and read circuits.<ref name="fsm">Atari, Inc., ''1050 Disk Drive Field Service Manual'' (FD100330): power supply p. 1-8; disassembly and connector polarity pp. 3-1 and 3-2; symptom checklist p. 4-5; power supply waveforms p. 4-16; schematic sheets 1, 3 and 4 of 4 (Tandon), including note 2, "all capacitors are 80% -20%". Hosted here as [[:File:Atari 1050 Disk Drive Field Service Manual.pdf]].</ref><ref name="sams">Howard W. Sams & Co., ''Computerfacts'' CD13, ''Atari Model 1050 Disk Drive'' (1987): schematic with values and DC voltages; parts list p. 9 (C2 0.68 µF 35 V, C41 4.7 µF 16 V); general note that values in brackets are used in some versions. Hosted here as [[:File:Sams Computerfacts CD13 Atari 1050 Disk Drive.pdf]].</ref> Atari's parts list gives no capacitor values, but its schematic sheets do, and most of them also give the voltage rating. Where Atari's sheets give no rating, the table uses the Sams parts list or Console5's list.<ref name="console5">Console5 TechWiki, "Atari 1050", capacitor list (last edited 14 July 2022). [https://wiki.console5.com/wiki/Atari_1050 wiki.console5.com]. Secondary source.</ref>

== Signs of failure ==

* +12 V missing at TP14 or +5 V missing at TP13. Atari's checklist names C71, with CR15 and CR16, for a dead +12 V doubler.<ref name="fsm" />
* Excess ripple at the regulator inputs. On the Sams schematic Q7's input sits at 9.8 V and Q8's at 17.8 V DC.<ref name="sams" />
* Bulged, leaking or crusted capacitors around the power supply at the rear of the board.

See [[Capacitor Failure Symptoms]] for general signs.

== Capacitor list ==

{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''Atari 1050 electrolytic capacitors'''
! Ref !! Value !! Voltage !! Where it sits !! Notes
|-
| C67 || 4,700 µF || 35 V (Atari) || Input of Q7 (7805), after the bridge rectifier || Console5 lists 25 V; the Sams schematic shows 9.8 V DC here
|-
| C68 || 4,700 µF (Atari); 6,800 µF (Sams) || 35 V (Atari) || Input of Q8 (7812), after the doubler || Sams shows 17.8 V DC here
|-
| C71 || 4,700 µF (Atari); 6,800 µF (Sams) || 35 V (Atari) || Voltage doubler, with CR15 and CR16 ||
|-
| C69 || 47 µF || 16 V (Atari) || Output of Q7, +5 V ||
|-
| C70 || 47 µF || 16 V (Atari) || Output of Q8, +12 V ||
|-
| C41 || 4.7 µF || 16 V (Sams) || +5 V supply line || Atari's sheet 3 gives no rating
|-
| C42 || 47 µF || 16 V (Atari) || +12 V supply line ||
|-
| C21 || 4.7 µF || 16 V (Atari) || +12 V line, with L4, sheet 1 || Console5 lists 35 V
|-
| C43 || 47 µF || 16 V (Atari) || Collector of Q6 (TIP110), the 12 V feed to the spindle motor switch, after L6 ||
|-
| C44 || 2.2 µF || 50 V (Console5) || Across the spindle motor connection, J1 pins 1 and 2 || Atari's sheet 3 gives no rating
|-
| C51 || 1 µF || 50 V (Console5) || U5 (LM2917) speed control loop || Atari's sheet 3 gives no rating
|-
| C2 || 0.68 µF || 35 V (Sams) || Read amplifier U22 || Not on Console5's list
|}

Values and positions are from Atari's schematic sheets, cross-checked against the Sams schematic; the source of each rating is in brackets.<ref name="fsm" /><ref name="sams" /><ref name="console5" /> The Sams sample had 6,800 µF at C68 and C71, with 4,700 µF in brackets, Sams' mark for a value used in some versions.<ref name="sams" /> Atari's own figure is 4,700 µF at 35 V for all three large capacitors, and its schematic gives every capacitor a tolerance of +80/-20 %.<ref name="fsm" /> Check the board for the parts actually fitted, and note the orientation of each capacitor before removing it.

== Procedure ==

# Unplug the adaptor and the SIO cables.
# Open the drive and lift out the mechanism as described in the [[Atari 1050 Maintenance Guide]], noting the plug positions.<ref name="fsm" />
# Unclip the board from the bottom cover, where it sits over three alignment guides.<ref name="fsm" />
# Replace the capacitors one at a time, matching polarity to the board markings.
# Refit the board and mechanism, plugging each connector by the wire colour order in figure 3-1 of the service manual.<ref name="fsm" />

== Checks after recapping ==

{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''Voltages to check'''
! Point !! Expected !! Source
|-
| TP13 || +5 V DC || FD100330 p. 4-16<ref name="fsm" />
|-
| TP14 || +12 V DC || FD100330 p. 4-16<ref name="fsm" />
|-
| Q7 input (across C67) || 9.8 V DC || Sams CD13<ref name="sams" />
|-
| Q8 input (across C68) || 17.8 V DC || Sams CD13<ref name="sams" />
|}

Then run the power-up self test and the diagnostic diskette's automatic tests, described on the [[Atari 1050 Drive Troubleshooting]] page.

== Related pages ==

* [[Atari 1050]]
* [[Atari 1050 Maintenance Guide]]
* [[Atari 1050 Drive Troubleshooting]]
* [[Atari 1050 Documentation]]
* [[Capacitor Failure Symptoms]]
* [[Recommended Tools]]

== References ==

<references />

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[[Category:Atari Systems]]
[[Category:Capacitor Replacement Guides]]
[[Category:Atari Capacitor Replacement Guides]]