AllenHeath-GL4-mix-sm3 电路图 维修手册.pdf

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1、RadioFans.CN 收音机爱 好者资料库 RadioFans.CN 收音机爱 好者资料库 RadioFans.CN 收音机爱 好者资料库 TECHNICAL BULLETIN To: From:ARJ Date:22 December, 1999 Subject: GL4 Mute Group Lock-Up Due to a change in specification to the BC549 transistors, some production consoles will have these devices fitted reversed on the MONO PCB,

2、AG2005A. These transistors, Q2 and Q14, are part of the power-on reset circuit for the mute processor, and although they will function in the incorrect position, they can cause the mute systems in certain consoles to lock up when first switched on from cold. Normally they will resume correct operati

3、on within a few minutes. This may be more noticeable if the DC supply voltage is lower than the +/- 16V specified. If startup problems are encountered, then check these transistors for orientation, and reverse or replace them if necessary. With the console inverted on a suitably sized clean work sur

4、face, clear of parts and debris, and with a cloth to protect the console cosmetics, remove the base and locate the +5V regulator IC12, (identified by the black finned heatsink fitted to it) on the MONO PCB. The two transistors are to one end of the heatsink, next to a 330uF capacitor (C5). Check wit

5、h the diagram and correct if needed. NOTE The overlay in the service manual shows the incorrect orientation for the BC549 transistors. They should be positioned as the other transistors on the assembly. BC549 transistors ?CORRECT ?INCORRECT STEP 1. For Direct out ? Pre-fade cut link J37 add ? a link at J38 STEP 2. All pre-fade signal is pre-EQ ? by default.? All pre-fade signal is post-mute by ? default.? To get pre-fade direct out, pre-mute ? (unaffected by channel mutes) cut ? J35, add a link at J36