08/sep/2026 22/04 - Roland PSB-1U - repair   

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Roland PSB-1U
input: 90-260V AV
output: 9V DC, 2A, center-negative

Description:
A switching power supply.
Output filter is 1000uF(low esr) cap with a ceramic under it, choke, and 470uF(low esr) cap
Feedback loop is optocoupler and a TL431. VCC to pwm controller is 15-16V.

The fucky wucky:
Was random and non-repeatable on every power cycle after letting it rest:
slow sawtooth ripple(1Vpp+ at no load)
high frequency bursts every 8ms(0.5Vpp+, at no load and at full load)
constant high-frequency ripple(0.5Vpp, at standby or full load)

The fix:
The pwm controller is an SG6848(also marked as AAHxx(xx is date code)) in a 6-pin SOT-26 package.
Replacements include OB2263MP, LD7535, and CR6848.
I swapped the SG6848 for an OB2263MP due to very wide availability.

I strongly suggest a hot air station or a fine tipped soldering iron, and loads(and i meand LOADS) of flux.
Just because i could do it with a soviet era soldering iron and a used wedge tip,
doesn't mean that you should try it that way, you are more than likely to blow something up

Discharge the big cap through a resistor, don't get killed

The resulting stats:
After the swap: 9.37V output, ~10mVpp ripple with no load.
With EDIROL V-8 mixer connected in standby ripple grows to about 0.4Vpp

if roland wants to sue me for sharing all this info and photos,
good luck getting through the iron curtain :)