Regarding transformer repair for the SC-88 Pro. \ VOGONS

Regarding transformer repair for the SC-88 Pro.

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First post, by zwrr

Posted on 2026-05-13, 03:27

zwrr Offline

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A friend gave me a faulty SC-88Pro. The problem is that it won't power on and doesn't respond at all. After disassembling it, I found that the power supply section wasn't outputting 12V or 5V. I removed the transformer and further measured it, finding that the 12V and GND output sides of the transformer were short-circuited, with a resistance of only about 4 ohms. It's clear the transformer is damaged. I'd like to know what can replace this transformer? It has both 12V and 5V outputs; what power output transformer would be needed for the replacement? Can a small computer power supply be used as a replacement?

SBC1: Cyrix 5x86-120, HS-5x86HVGA, 16MB EDO, GD54M30, SB Pro II, HardMPU-wt
SBC2: VIA C3-800, PCISA-C800, 128MB SDRAM, Savage4 Pro, SB AWE64 Gold
SBC3: Tualatin-S 1.4G, PCI-6872, 256MB SDRAM, FX5200 PCI, Voodoo2 SLI, SB Live

Reply 1 of 2, by zwrr

Posted on 2026-05-13, 08:26

zwrr Offline

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Joined: 2022-10-06, 23:57

The problem has been solved. I disassembled and inspected the transformer, finding it completely burnt out. Finding a transformer of the same specifications seemed difficult. After carefully reviewing the repair manual, I discovered I only needed +5V, +12V, -12V, and a RESET signal. So, I tried using an ATX power supply. I removed five components: S1VB20, S5VB20, PQ05RR1, 78M12, and 79M12. Then, I connected the ATX power supply's +5V to the output pin of PQ05RR1, the PG signal to the reset signal output of PQ05RR1, the +12V to the output pin of 78M12, and the -12V to the output pin of 79M12. Now it works perfectly.

Because the ATX power supply is too large to fit in the case, I plan to install a DC-ATX power module to convert the SC-88 Pro to use a 19V laptop power supply.

The attachment sc-88pro 电源.jpg is no longer available

The attachment sc-88pro atx.jpg is no longer available

Reply 2 of 2, by st31276a

Posted on 2026-05-13, 19:22

st31276a Offline

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Location: South Africa

Step down transformer secondaries are supposed to have low resistance.

Perhaps the primary winding was burnt or broken.

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