Film-Tech Forum ARCHIVE: Issue with Modified CP55 and CE SG1 card

This is topic Issue with Modified CP55 and CE SG1 card in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by William T. Parr (Member # 677) on 06-21-2007, 11:50 AM:

I have an iteresting problem that I hope someone else has had and can help me out with. The issue is I have a CP55 that has the split surround card and has had the backplane modified for such. This unit also has and external SRA5 adapter for playing Dolby SR, again modiedfied per the SRA 5 book. When the pink noisse card is in the 85C slot and the LE switch is set to tone I am not able to get a bass signal on the cat 442 card. However if I take a jumper from pin J13 A9 to pin D of the 442 card I will get Pink noise in the sub channel. If I replace the SG1 with the cat 150 card and run film I get Sub input to the card and output to the amp like I should. Any reason I can not get it directly from the SG1 card without the jumper on the backplane? is this required after the mod to set the sub level with the SG1? any help would be greatful.

Posted by Steve Guttag (Member # 268) on 06-21-2007, 05:11 PM:

Double triple check your backplane mods...in particular the one relating to the 105K resistor that should have been added between the Cat 441's A and D pins. Its job is to get the PN signal to correct locations at the right levels. With the Cat 241, PN went straight to the OBE card on pin D (and is shared with the J18 Dsub). However, with the CP65, Dolby changed how they worked with bass extension...instead of something that was applied the raw Lt/Rt signals, it became something that augmented any of the three stage changes so it is now post-decode (2:4). The Cat 441 follows this philosophy.

It was a bit late in the game to completely rewire the CP55's back plane for that so they made Left/Right inputs correspond to the Lt/Rt input of the Cat 241. D became the Center input.

A is now the pink noise generator input so you will need that jumper wire shown in the mod. The orginal trace that went to D is cut...the Pink Noise side of the cut trace (towards the right as you face the motherboard from the rear) is jumped to "A" . With this wire your pink noise has its proper input.

However, all is not the same as with the CP65 due to the LCR vs LtRt thing so a corrective amount of PN is added to the Center input via the resistor to make it calibrate properly. It also allows one to reinstall a Cat 241, though the PN level will be wrong.

So, step 1...make sure the mod was done completely and properly...that there is a wire going from a cut trace to pin A and that there is a 105K resistor going from pin A to pin D. It is possible that when the trace was cut, the person did not strip back the solder mask and tin the trace below and merely got the flux to stick the wire to the PCB without making any electrical contact. You can run your jummper from the Cat 85 A9 straight to the Cat 441 A pin too (don't forget the resistor though).

Steve