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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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previous page: 13.011 Recently I was using my GS and smoke started coming from the inside. Now my ADB peripherals (KB and mouse) don't work! It looks like the smoke came from an 8-legged module in the upper leftmost corner right behind the composite video connector and ADB jack. What's wrong? How can I fix my GS?
  
page up: Apple II Csa2 FAQs
  
next page: 13.013 I have 256kB on my 1MB Apple IIgs Memory Expansion Card. How do I add more memory and set the jumpers?