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Repair of the Meade 1812 Electronic DC Adapter 

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By Bill Castro
August 2002

Notes on repair of Meade #1812 Electronic DC adapter. This article is intended for those who are familiar with electronics and electronic repair.

The circuit is based on the Linear Technology ( linear-tech.com ) LT1170CT switching regulator IC. The schematic is shown on page 1 of the Linear Technology data sheet and also shown below. It is a boost converter. The assembly drawing for the Meade 1812 showing component placement is also shown below. The parts list with replacement parts is given below. Reference designators listed on the material list relate to the vendorís schematic. Electronic components are available from mail order supplier Digi-Key via phone (800-344-4539) or internet ( digi-key.com ). Other remaining materials can be found at Digi-Key and/or Radio Shack.

I would also recommend using a 3 amp fuse with the input. If the adapter fails, most likely it requires replacing inductor L1 (330uH, 1.6A), switching regulator IC U1 (LT1170CT) and diode D1 (1N5821). All parts are available from Digi-Key mail order supplier via phone (800-344-4539) or via the internet (digi-key.com). 

PARTS LIST

Listed as reference designator; part number; description; manufacture; digi-key part number; price as of 8/02.

U1; LT1170CT; IC, SWITCHING REGULATOR; LINEAR TECH; LT1170CT-ND; $10.63
R1; MFR-25FBF-16K9; RES,MF,1%,1/4W,16.9K; YAGO; 16.9KXBK-ND; $0.108
R2; MFR-25FBF-1K24; RES,MF,1%,1/4W,1.24K; YAGO; 1.24KXBK-ND; $0.108
R3; MFR-25FBF-1K00; RES,MF,1%,1/4W,1.00K; YAGO; 1.00KXBK-ND; $0.108
C1; ECE-A1HN010U; CAP,ALE,50V,1UF; PANASONIC;  P1196-ND; $0.37
C2; ECA-1VFQ391; CAP,ALE,35V,390UF,1.2Arms; PANASONIC; P5737-ND 
C2 alternate; EEU-FC1V391S; CAP,ALE,35V,390UF,1.2Arms; PANASONIC; EEU-FC1V391S; $1.13
C3; ECA-1VFQ560; CAP,ALE,35V,56UF,0.29Arms; PANASONIC; P5728-ND; 
C3 alternate; EEU-FC1V680; CAP,ALE,35V,63UF,0.29Arms; PANASONIC; P10292-ND; $0.42
L1: 5900-331; INDUCTOR,1.6A,330UH; J. W. MILLER, M5924-ND, $3.82
D1: 1N5821; DIODE,SCHOTTKY,3A,30V; DIODES, INC.; 1N5821DICT-ND; $0.68
HS1; 577002B00000; HEATSINK, TO220 AAVID; HS105-ND; $0.39
HOUSING; 1591ASBK; BOX BLK 3.9X2.0X0.8"; Hammond Mfg;  HM102-ND; $3.18
P1; 760; POWER PLUG 2.5MM BLACK;  Switchcraft;  SC1051-ND; $2.92

 

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Assembly Drawing

Schematic

 


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