Atari ST Capacitor Replacement Guide

A long-case ST. The internal power supply sits in the base beside the main board.

Capacitor replacement for the original Atari ST family: the 260ST, 520ST, 520ST+, 520STM, 520STF, 520STFM, 1040ST, 1040STF and 1040STFM. The main board lists below are by board number, which is printed on the board. For the STE see Atari STE Capacitor Replacement Guide; for diagnosis see Atari ST Troubleshooting Guide.

Warning: the long-case machines have a mains switching supply inside the case, and its primary reservoir capacitor holds a dangerous charge after the machine is unplugged. Discharge it and check it with a meter before touching the primary side.

Signs of failure

• Random crashes. exxos measured about 1 V of ripple on the 5 V output of an unrecapped Mitsumi SR98 supply, enough to cause random crashes.
• The picture dims when the floppy motor starts. On the SR98 exxos traced this to the regulation circuit as well as the capacitors (see below).
• Leaking or bulging capacitors. See Capacitor Failure Symptoms.

Do the supply first: a failing supply produces faults that look like main board faults. exxos lists recapping the supply as a mandatory fix for every ST, and warns that some supplies have a capacitor fitted backwards from the factory, so check each part against the polarity marked on the board as it comes out.

Main board capacitors

The short-case 260ST, 520ST and 520ST+ use board C070243; the long-case machines use C070523, C070789, C103088 or C103225, and Console5 also lists a late C103572. Except where an Atari document is named, the lists below are Console5's community lists, read from boards and not taken from Atari documents.

exxos ties two common main board faults to ageing electrolytics. A machine that will not start until the reset button is pressed usually has tired capacitors in the reset timer; on a C070789 Rev D board he identifies them as C2 and C7. When an STFM's picture flashes or loses sync on a television or monitor, he found failed electrolytics in the video circuit as well as sync timing that modern televisions handle badly; his kit for it replaces three 10 µF, one 1 µF, one 33 µF, three 100 µF and one 470 µF part.

C070243 (short case)

Console5 gives three revisions. One 470 µF part on the Rev B and Rev C boards has no printed designator, and the keyboard's own board carries a 100 µF 25 V part. Atari's keyboard schematic, drawing C070075, shows the same 100 µF 25 V part across the keyboard's supply.

Atari's 520ST/260ST schematic, drawing C070231 revision M (April 1986), covers assembly CA070052 with and without the television modulator and does not name the bare board. It shows two 470 µF parts on +5 V: C106 at the power input after the switch SW1, and C104 feeding the RAM through L29. It gives 22 µF at C50 and C55 (the reset timer U37) and at C105 (the 68000's supply), 1 µF at C31 and C34 (audio coupling) and 47 µF at C33 (audio output). On that drawing C56 is a 68 pF ceramic in the 32 MHz oscillator. Console5's Rev C and Rev H lists give 100 µF at C31 and 47 µF at C34, so read the values printed on the parts before ordering.

C070243 Rev B (Console5)

Position	Value	Voltage
C31	1 µF	50 V
C33	47 µF	25 V
C34	1 µF	50 V
C50	22 µF	16 V
C55	22 µF	16 V
No designator	470 µF	16 V
Keyboard board	100 µF	25 V

C070243 Rev C (Console5)

Position	Value	Voltage	Notes
C31	100 µF	25 V
C33	47 µF	25 V
C34	47 µF	16 V
C50	22 µF	16 V
C55	22 µF	16 V
Not given	470 µF	16 V
C105	22 µF	16 V
No designator	470 µF	16 V
Keyboard board	100 µF	25 V	Axial

C070243 Rev H (Console5)

Position	Value	Voltage	Notes
C31	100 µF	16 V
C33	47 µF	16 V
C34	47 µF	16 V
C50	22 µF	16 V
C55	22 µF	16 V
C56 (uncertain)	470 µF	16 V
C104	470 µF	16 V
C105	22 µF	16 V
Keyboard board	100 µF	25 V	Axial

C070523 (early 1040STF)

Atari's 1040 STFM parts list, dated 1 May 1986, gives the electrolytics below; it does not name the bare board. Its positions and values match Console5's list for C070523-001 Rev B and Rev C except for one designator.

Atari's 1 May 1986 parts list (matches Console5's C070523 Rev B / Rev C)

Position	Value	Voltage	Notes
C7	22 µF	16 V	Axial
C8	22 µF	16 V	Axial
C9	47 µF	16 V	Axial
C12	1 µF	50 V	Axial, non-polarised
C14	1 µF	50 V	Axial, non-polarised
C25	4.7 µF	25 V	Axial
C27	4.7 µF	25 V	Axial
C29	4.7 µF	35 V	Axial, non-polarised
C30	4.7 µF	25 V	Axial
C35	470 µF	16 V	Radial
C43	100 µF	25 V	Radial. Console5 lists this part as C48; Atari's list has C48 as a 12 pF ceramic
C71	22 µF	16 V	Radial
C105	470 µF	16 V	Axial

Console5's list for Rev D boards, which have a large 2200 µF part at C35, differs at C12, C14 and C35 and adds a 100 µF part:

C070523 Rev D (Console5)

Position	Value	Voltage	Notes
C7	22 µF	16 V
C8	22 µF	16 V
C9	47 µF	16 V
C12	100 µF	16 V
C14	47 µF	16 V
C25	4.7 µF	25 V
C27	4.7 µF	25 V
C29	4.7 µF	35 V	Non-polarised; Console5 says 25 V parts are acceptable
C30	4.7 µF	25 V
C35	2200 µF	16 V
C71	22 µF	16 V
C105	470 µF	16 V
No designator	100 µF	16 V	Added above C41, not on the C41 pads

C070789 (520STFM and 1040STFM)

C070789-001 Rev C / Rev F (Console5)

Position	Value	Voltage	Notes
C2	22 µF	16 V
C7	22 µF	16 V
C9	47 µF	16 V
C11	100 µF	16 V
C12	47 µF	16 V
C22	100 µF	16 V
C49	1000 µF	16 V
C70	100 µF	16 V
C73	100 µF	16 V
C74	4.7 µF	35 V	Non-polarised
C75	4.7 µF	35 V
C92	100 µF	16 V
C148	100 µF	16 V
C149	4700 µF	16 V
C215	1 µF	50 V
C216	10 µF	16 V
C217	10 µF	16 V
C218	10 µF	16 V
C219	33 µF	16 V
C220	100 µF	16 V
C221	100 µF	16 V
C223	470 µF	16 V

C103225 and C103572 (late STFM)

Console5's list for C103225 (Rev 1 and Rev 2) is the C070789 list without C22 and the C215–C223 group. C103572 Rev 1 adds C190, 100 µF 16 V.

C103225 Rev 1 / Rev 2; C103572 Rev 1 adds C190 (Console5)

Position	Value	Voltage	Notes
C2	22 µF	16 V
C7	22 µF	16 V
C9	47 µF	16 V
C11	100 µF	16 V
C12	47 µF	16 V
C49	1000 µF	16 V
C70	100 µF	16 V
C73	100 µF	16 V
C74	4.7 µF	35 V	Non-polarised
C75	4.7 µF	35 V
C92	100 µF	16 V
C148	100 µF	16 V
C149	4700 µF	16 V
C190	100 µF	16 V	C103572 only

Power supply capacitors

The short-case machines use an external linear supply; the long-case machines have an internal switching supply, made by one of several manufacturers. Identify the supply from its label. All lists are Console5's community lists, read from supplies, unless another source is named.

Mitsumi SR98 / SR118 / 68-4231A

Mitsumi SR98 / SR118 / 68-4231A (220–240 V)

Position	Value	Voltage	exxos replacement
C104	47 µF	400 V	68 µF 400 V
C201	2200 µF	10 V	4700 µF 16 V
C202	2200 µF	16 V	4700 µF 16 V
C203	2200 µF	10 V	4700 µF 16 V
C204	1000 µF	16 V	1500 µF 16 V
C205	1000 µF	10 V	1500 µF 16 V
C206	1 µF	50 V	Not listed

The replacement column is exxos's parts list, which also fits a KBU1005 10 A 600 V bridge rectifier in place of the original 2 A part. exxos measured the old parts at 42 µF (47 µF), 1868–1951 µF (2200 µF) and 887–975 µF (1000 µF). For the picture dimming during floppy access, exxos replaced R202 with 1 kΩ and R201 with 1.2 kΩ and then reset the 5 V preset.

Mitsumi SR97 / 68-4242A (110–120 V)

Mitsumi SR97 / 68-4242A

Position	Value	Voltage
C104	220 µF	200 V
C201	2200 µF	16 V
C202	2200 µF	10 V
C203	1000 µF	16 V
C204	2200 µF	10 V
C205	1000 µF	10 V
C206	1 µF	50 V

Astec ASP34 / ASPF34-1

Astec ASP34 / ASPF34-1

Position	Value	Voltage	Notes
C4	47 µF	250 V
C5	47 µF	250 V
C7	330 µF	25 V	Sometimes 35 V; Console5 supplies 35 V
C9	100 µF	25 V
C14	330 µF	25 V	Sometimes 35 V; Console5 supplies 35 V
C15	330 µF	25 V	Sometimes 35 V; Console5 supplies 35 V
C13	4700 µF	16 V
C12	2200 µF	16 V	Atari's ASP34-1 schematic gives 25 V

Atari's own schematic of the ASP34-1, printed in the Mega service manual, has the same positions and values, rates C12 at 25 V and also shows C8, 1 µF 16 V, on the primary side; see Atari Mega ST Capacitor Replacement Guide#Power supply (ASP34-1). exxos's ASP34-2 had 35 V parts at the three 330 µF positions.

DVE DSP-508A / DSP-508AA

Console5 notes that the published schematic's parts list differs considerably from production supplies.

DVE DSP-508A / DSP-508AA

Position	Value	Voltage	Notes
C3	47 µF	250 V
C4	47 µF	250 V
C8	330 µF	25 V
C9	1 µF	50 V
Not given	100 µF	25 V	In heat-shrink, near the safety capacitor at the top of the board
C22	2200 µF	16 V
C25	2200 µF	16 V
C23	330 µF	25 V
C20	330 µF	25 V

exxos measured the parts in a DSP-508A: two 47 µF 250 V, three 330 µF rated 35 V on his supply, and two 2200 µF 16 V. He replaced the 330 µF parts with 680 µF 25 V and the 2200 µF parts with 4700 µF 16 V.

FPK-N3 5657-B001-1

FPK-N3 5657-B001-1

Position	Value	Voltage
C5	220 µF	200 V
C8	47 µF	16 V
C9	47 µF	16 V
C101	470 µF	25 V
C103	100 µF	25 V
C201	2200 µF	10 V
C202	2200 µF	10 V
C203	470 µF	10 V
C102	470 µF	25 V
C205	Not fitted
C303	1 µF	50 V

Atari (Japan)'s drawing "Typical 1040STF(M) Power Supply" in the field service manual uses the same designators and values: C5 220 µF on the primary side, C8 and C9 47 µF, C101 and C102 470 µF, C103 100 µF, C201 and C202 2200 µF, and C303 1 µF. It leaves C203's value blank and gives no voltage ratings.

C070091-014 / Model 1103 (520ST external supply)

Console5 has no designators for this supply; replace by value: 4700 µF 16 V, 2200 µF 25 V, 220 µF 25 V, 100 µF 25 V and 10 µF 25 V, one of each.

Floppy drive capacitors

For the TDK D357 (T41V) drive fitted in some long-case machines, Console5 lists by value: two 22 µF 16 V, two 47 µF 16 V, one 10 µF 25 V, one 4.7 µF 35 V, one 2.2 µF 50 V, five 0.47 µF 50 V and one 3.3 µF 50 V. See also Floppy Drive Repair.

Procedure

1. Open the case as described on Atari ST General Maintenance#Opening the case. On a long-case machine, take the supply out before working on it.
2. Photograph each board and note the polarity of every electrolytic. Mark the non-polarised positions.
3. Remove one capacitor at a time and fit its replacement before moving on.
4. Fit non-polarised (bipolar) parts where the list says non-polarised.
5. Use parts of the same value and at least the same voltage rating. In the supply, use low-ESR parts made for switching supplies; exxos warns that cheap capacitors can overheat or explode there.
6. Clean off flux and check for solder bridges.
7. Do not run a switching supply without a load. To test one on the bench, exxos uses a 2.2–4.7 Ω resistor of at least 10 W on 5 V and a 22 Ω, 10 W resistor on 12 V.

After recapping

On a long-case machine, set the 5 V output with the single preset to within ±5 % (4.75–5.25 V); the same preset moves +12 V. The short-case external supply has no adjustment. The machine draws up to 2.3 A at 5 V and 340 mA at 12 V during disk access, so check the 5 V output with the drive running.

Related pages

• Atari ST General Maintenance
• Atari ST Troubleshooting Guide
• Atari STE Capacitor Replacement Guide
• Atari 520ST and 1040ST Computer Field Service Manual
• Capacitor Failure Symptoms
• Recommended Tools