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Date Posted: 05:48:19 01/31/02 Thu
Author: Potter
Subject: Re: Potter's 5508w schematic
In reply to: sphinx 's message, "Re: Potter's 5508w schematic" on 04:10:50 01/31/02 Thu

No schematic, just some bits & pieces I traced out which exist only as pencil scribbles on scraps of paper. This most likely will not be a problem if the changes were an attempt to beat the decoder section as my mods simply bypass all of it by feeding the output of the IF circuit via the 3Chip to the output buffer, the Jerrolds decoder circuitry could all be removed with the exception of the AGC sample & hold section. A quick test would be to do the tuner mods first (program and wire in the tuner PIC16F84A) and connect directly from W304 to the top end of cut W428 (see the diagram in the tuner files). With a good signal source ie downconverter antenna connected any non-scrambled channels will go through perfectly and the sound will be OK on all channels (I'm assuming the channels in your area are on the same frequencies as mine, if not they'll need to be identified and the tuner PIC code modified to suit) I'm in Van Diemens Land (OZ) if that helps to narrow it down. Cutting W428 disconnects the output of the OSD chip which produces the dreaded blue screen with the 'box disabled - please call' message. If this test works the box is OK to wire in the decoder board.
There's simple PCB layout in the tuner files for doing this tuner test - during my early experiments one of these was floating around in the box, wrapped in a sandwich bag, for several months. If everything works out OK just unplug the tuner PIC and put it in the full board when ready (use IC sockets) - the sandwich bag and masking tape proved to be a very reliable option though.

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