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Found 3 results

  1. Hey folks, I'd be grateful for a little guidance in pinpointing a voltage problem with my AU-4900 please. Having read dozens of forums here on SNA and on AK, I've tried all of the known weak points (I think). It seems my issue is not uncommon so I hope I'm just missing something simple. I'm especially thankful for the knowledge shared by @skippy124 - I thoroughly enjoy your work John! I'm handy with a soldering iron and have all the common test equipment and my trusty DBT. Problem: Amp won't come out of protection mode due to high voltages on Left output devices. Initially, I was able to adjust the VRs to get the bias set correctly but then protection kicked in. As the voltages to the Right amp section seem good and the PS section is sending the correct voltages out, my first thoughts was that this is a protection circuit issue. I've basically replaced all components in the protection circuit, to no avail. I've also replaced all of the transistors on the tone board and 90% on the amp board and all diodes on the amp board bar the Zener (on order). Replacing components has not fixed the issue, nor made is worse. I've attached a circuit diagram of the protection circuit with some voltages (via a DBT). Here are the components I've replaced: Amp Board D01, 02 -> 1N4148 D605, 607-615 -> 1N4007G TR601, 602 (SDC1364) -> KSC1945CGTA TR15, 16 (2SC711) -> KSC945CGTA C602 -> 1uF 63V WIMA MKS2 C604 -> 470uF 25V Panasonic FM C605 -> 100uF 50V Panasonic FM TR601, 602, 602 (2SC1364) -> KSC945CGTA TR03, 04 (2SC1951) unchanged and tried swapping from a working 4900 TR05, 06 (2SC711) unchanged and tried swapping from a working 4900 TR07, 08 (2SD438) -> KSC2690AYS TR09, 10 (2SB560) -> KSA1220AYS TR11, 12 (2SD188A) unchanged TR13, 14 (2SB545A) unchanged IC1, 2 (dual 2SA798) -> paired KSA992FTA with matching Hfe Fusable resistors R37,38,39,40 I've also swapped out the 4 germanium diodes from a working 4900. Tone Board All (2SA726) -> KSA992FTA All (2SC1313) -> KSC1845FTA Voltages on output devices: TR14 E= -29.5mV, B= -629mV, C= -29.6V TR13 E= 24.75V, B= 24.75V, C= -29.62V TR12 E= 20mV, B= 600mV, C= 29.68V TR11 E= 24.78V, B= 24.95V, C= 29.68V I've even tried removing the output devices but that has no effect on the Left voltages. Any other measurements that would be helpful for diagnosis, please shout. Thanks in advance. Brad
  2. I have rotel rb-981 power amplifier..However it powers up and protection light goes off.
  3. * Item full name and model etc. THOR Smart Board * Location Woolloomooloo/CBD * Item condition description 10 / 10 (brand new still in box) * Price and price conditions $150 + Postage (RRP 299) * Reason for selling Not needed - came with PS10 * Payment Methods: Bank Transfer / Paypal / COD * Extra Info: Massive 208,000 AMP MaxiMuM spike 6080 jOULES http://thortechnolog...2bf-smart-board http://thortechnologies.com.au/images/products/A12BFv11.pdf Intelligent Power Conditioning Filter Dynamic Active Tracking Circuitry 3 In 1 Isolation Bank 1 = 1 outlet Bank 2 = 3 outlets Bank 3 = 4 outlets 8 Outlets All in the one compact board Data & Aerial Protection With Cable TV connection Fibre Optic And Broadband Compatible Multiple Application Identity Tags 6 Year Free Replacement Warranty Designed and Engineered in Australia 100% Australian Owned And Compliant
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