13.012 My ROM-01 GS has an odd postage stamp size circuit board tacked onto the motherboard near the front edge. What is the board for?
Description
This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
13.012 My ROM-01 GS has an odd postage stamp size circuit board tacked onto the motherboard near the front edge. What is the board for?
The circuit on the mini-board is a low-gain 1-transistor amplifier which
seems intended mainly as a buffer/voltage-level shifter between the 'old Apple'
sound output of the Mega Chip and Op Amps which drive the Speaker and Sound
jack.
On the underside of the motherboard, beneath the boardlette, a surface-
mounted resistor (SR1) has been scratched out. Leads from the mini-board run to
SR1's connection points as well as Ground and a +12V supply point near Op Amp
UM12.
The circuit does not appear in the GS 'Hardware Reference ROM-01
schematics; but, it is shown in ROM-03 schematics. Some ROM-01 GS's do not have
the mini board; so, it seems likely that the circuit was included on-
motherboard in later ROM-01's and all ROM-03's. By the way, the circuit was
certainly installed at the time of manufacture and was not part of the standard
ROM-00 to ROM-01 upgrade.
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