Sharp X68000 XVI Capacitor Replacement Guide

Sharp's circuit diagram of the SH4 power supply, board UADP-0069CEZZ, from the XVI service manual. The primary side is on the left, the +12 V, −12 V and +5 V outputs at the top right and the T2 standby converter at the bottom.

The Sharp X68000 XVI (CZ-634C and CZ-644C) is the one X68000 for which Sharp's own service manual is available, and its circuit diagrams print a value and voltage beside every electrolytic capacitor in the machine. The tables below are read from those diagrams. The manual has no parts list, so it gives no capacitor series, temperature ratings or case sizes; Poe's notes, quoted below, give the series he found on the SUPER, and the cans on your own boards are the final word.

The power supply, which owners call the SH4, is the same board (UADP-0069CEZZ) in the Sharp X68000 EXPERT, EXPERT II, Sharp X68000 SUPER, XVI and Sharp X68030, so the supply table and the procedure below apply to all of them. Its capacitors are the ones that leak and stop the machine; for the general signs of a failing capacitor see Capacitor Failure Symptoms.

Warning: the supply runs from 100 V mains, and the primary side keeps more than 100 V DC on the reservoir capacitor C9 (470 µF, 180 V) after the plug is pulled. Unplug the machine, wait, and measure across C9 before you touch the primary side.

Power supply (SH4, UADP-0069CEZZ)

SH4 power supply electrolytics (XVI service manual, printed pages 97 and 98)

Ref	Value	Voltage	Position on the diagram
C9	470 µF	180 V	Primary reservoir, after bridge DB1
C24	1000 µF	25 V	Input of IC22 (SI3122V), +12 V
C25	680 µF	16 V	Output of IC22, +12 V
C27	220 µF	25 V	Input of IC23 (µPC78M12HF), −12 V
C28	100 µF	16 V	Output of IC23, −12 V
C40	5600 µF	10 V	+5 V, after rectifier D27
C41	5600 µF	10 V	+5 V, after rectifier D27
C42	2200 µF	6.3 V	+5 V, after choke L21
C35	10 µF	25 V	Power control circuit round Q33 and ZD32
C38	3.3 µF	50 V	Power control circuit round Q33
C31	100 µF	10 V	Primary side of the T2 standby converter, with Q31 and Q32
C33	220 µF	16 V	Input of IC31 (µPC78M05HF), +5 V standby (VCC2)
C34	100 µF	6.3 V	Output of IC31, VCC2

That is 13 electrolytics. Poe's list for the same supply in a SUPER gives the same 13 values and voltages and names the original series as ELNA RSG and RJ3. Sharp's X68030 diagram of the board, reproduced on the Sharp X68030 Capacitor Replacement Guide, gives the same values again.

Polarity of C27, C28 and C31

The service manual's diagram draws C27, C28 and C31 with the wrong polarity, and its transformer polarity dots cannot be trusted. Fram found this by measuring the voltage across C31 in a working supply: it matched the silkscreen on the board, not the diagram. The silkscreen is correct for all three. Before he found the error, Fram had fitted C31 the wrong way round following the diagram; after nine years that 100 µF capacitor measured 51 µF. Fit these three by the silkscreen, and photograph each one before you remove it.

Other notes on the supply

• Poe found C24, C27, C40, C41 and C42 leaking heavily in a SUPER's SH4. In Fram's XVI-HD the leaking capacitors were marked "Long Life"; the electrolyte had run onto the back of the board, onto the case and down the cable to the base board.
• An owner of an XVI found C27 marked 120 µF 25 V on his board, against 220 µF on the diagram.
• Poe's supply table gives R5 as 0.33 Ω and R36 as 220 Ω for the XVI's supply, and says that some have a heatsink on IC23, in which case R5 can be left alone if it has not failed. Sharp's diagram gives R5 as 0.39 Ω, 1 W.
• For the replacements Poe raised C9 to 250 V, C34 and C42 to 10 V and C35 to 50 V, and used the original voltages elsewhere.

Main board (K7243DE)

XVI main board electrolytics (service manual, main board diagrams)

Ref	Value	Voltage	Position on the diagram
C16	470 µF	10 V	+5 V (VCC1) input from the supply, connector B
C17	2200 µF	6.3 V	Video output stage, with Q4 (2SA1015Y)
C24	220 µF	6.3 V	Backup supply line VBT
C10	0.47 µF	50 V	IPL switch line, with R8 and R9

The diagrams also mark C22 (47 µF 10 V, on the DVCC supply pin of IC14, CXA1260) and C29 and C30 (1 µF 35 V, at the processor) as tantalum. The other capacitors on the main board are drawn as non-polarised parts. Poe's list for the SUPER's main board, a different board (6792DE), has four electrolytics of the same four values under other reference numbers.

Control board (K7244DE)

The control board in the base carries the floppy controller, the sound and ADPCM circuits, the headphone amplifier, the reset circuit and the backup battery.

XVI control board electrolytics (service manual, printed pages 85 and 86)

Value	Voltage	References
100 µF	16 V	C209, C211, C227, C235, C242, C259
100 µF	10 V	C234, C243, C261
100 µF	6.3 V	C210, C212, C224, C237, C238, C249
47 µF	16 V	C208, C252, C253
22 µF	16 V	C217
10 µF	16 V	C225
4.7 µF	50 V	C201, C202, C203, C204, C207, C226, C230, C260
1 µF	50 V	C218, C233, C258
0.47 µF	50 V	C231, C232, C236, C247, C264

That is 36 electrolytics. C209 (+12 V), C211 (−12 V) and C212 (+5 V standby) sit on the supply inputs at connector A; C217 and C218 are on the reset IC (IC209, TL7705); C234 and C261 couple the headphone amplifier (IC223, NJM2073) to the headphone socket, and C237 and C238 are on the same amplifier; C243 and C224 are on the supply of the ADPCM chip (IC225, MSM6258); C207 and C208 are at the floppy data separator (IC202, SED9420). Poe's list for the SUPER's control board has the same 36 references, values and voltages.

Analogue board (K7245DE)

XVI analogue board electrolytics (service manual, printed pages 93 and 94)

Ref	Value	Voltage
C403, C404, C405	470 µF	10 V
C407, C408, C410	100 µF	16 V
C406, C411	100 µF	6.3 V

C403 to C405 are in series with the red, green and blue outputs. Poe's SUPER list has the same eight, and he found this board one of the hardest in the XVI to take the capacitors out of.

Expansion slot section

C801 and C802 (47 µF 10 V) are on the +5 V and +5 V standby lines to the slots, and C803 and C804 (47 µF 16 V) on the +12 V and −12 V lines. Poe's SUPER list gives all four as 47 µF 10 V. The service manual specifies 16 V for C803 and C804, which carry the 12 V rails, so use 16 V parts there.

Keyboard

The keyboard has two electrolytics: C3 (2.2 µF 50 V) on the reset line of the 80C51 controller and C8 (100 µF 10 V) on its supply.

Floppy drives

The service manual does not cover the inside of the drives. Poe lists the capacitors of versions 03, 04 and 07 of the drive used from the ACE to the X68030: C13, C18, C20 and C22 (100 µF, Nichicon N728 low-profile), C10, C24 and C26 (10 µF 16 V), five unnumbered 22 µF 16 V, one 10 µF 16 V, one 1 µF 50 V and one 1 µF 50 V bipolar. His version table gives the four 100 µF parts as 6 V, his stock list as 16 V; read the cans before ordering. On the version 06 drive from an XVI the wheel board has C6 (0.1 µF 50 V), C7 (22 µF 16 V) and C8 (0.47 µF 50 V). Poe warns against removing the spindle or stepping motor just to reach the capacitors, because the head position is set against the index timing. See Floppy Drive Repair for general drive work.

Replacement procedure

Taking the supply out

1. Switch off at the front and at the rear main switch, and unplug the mains lead.
2. The service manual's disassembly drawings give the order: for each tower take out the three screws on the rear and slide the side cover off, then remove the parts in the numbered order shown.
3. The supply is in the left-hand tower seen from the front. In the drawings it comes out, fan and all, after two screws and its connectors are removed.
4. Before touching the board, measure across C9 and wait until it has discharged.

On the bench

1. Photograph both sides of the board. Note the polarity marking printed beside every capacitor; for C27, C28 and C31 the silkscreen, not the service manual, is right.
2. Poe soaked the SH4 board in isopropyl alcohol for about five minutes, just deep enough to cover the component legs, before taking the capacitors off, so that the electrolyte and dirt came away more easily. After removing them he cleaned both sides with a toothbrush and cotton buds. Fram took off every part that could not be washed, including the transformers, and washed the board.
3. Look for burnt areas. In Fram's supply the electrolyte had shorted the zener diode, R33, R34 and a transistor, the power transistor below them had burst, and the fuse had blown; he replaced all of them as well as every capacitor. On the diagram, R33, R34, the zener ZD31 (HZS7B-1L), Q31 and Q32 form the primary side of the T2 standby converter, together with C31.
4. Fit the new capacitors one position at a time, matching the value and using a voltage at least as high as the original.
5. If you replace ZD31, do not bend its legs sharply at the body. Fram fitted a 1 W zener with thick, stiff legs bent at the body, and the stress broke it. After he replaced it again the supply worked, but the fuse blew again a few hours later, a fault he had not traced when he wrote.

Testing

1. The SH4 turns its outputs on when its own main switch is on, so it can be tested out of the machine. Check the rails at the connectors against the table below.
2. Fram found the outputs unsteady when he first measured them after his repair; the machine started, and when he measured again after it had been running the outputs were steady.
3. If the supply still does not work after the capacitors, solder joints and burnt parts have been dealt with, the fault may be an open transformer winding or a failed transistor. Kunihiko Ohnaka has published in-circuit resistance readings taken from the solder side of a working SH4 board, which can be compared with yours to find the part.

After the recap

SH4 output connectors (service manual, printed pages 97 and 98)

Connector	Pins
A (control board)	A1 +5 V, A2 ground, A3 +12 V, A4 −12 V, A5 +5 V standby (VCC2), A6 power control
B (main board)	B1 +5 V, B2 ground
P and Q (floppy drives)	+12 V, ground, +5 V
D (hard disk)	D1 +5 V, D2 ground, D3 +12 V

The diagram gives nominal voltages only, with no tolerances. If a rail is missing or wrong, go to the Sharp X68000 XVI Troubleshooting Guide.

Related pages

• Sharp X68000 XVI
• Sharp X68000 XVI General Maintenance
• Sharp X68000 XVI Troubleshooting Guide
• Sharp X68000 XVI Service Manual
• Sharp X68000 SUPER Capacitor Replacement Guide
• Sharp X68000 EXPERT Capacitor Replacement Guide
• Sharp X68030 Capacitor Replacement Guide
• Capacitor Failure Symptoms