Induction is not heating.
Disconnect power from the unit. Open it up to gain access to the coil and controller. Disconnect the coil and use an ohmmeter to check its continuity. If it is open, replace it. Also inspect the connector pins and sockets to make sure they are not corroded or oxidized. (If the connector shell or the wire insulation at the connector show signs of overheating, this is very likely where the problem is.) Clean and polish, or replace the connector contacts if necessary.
If the coil, coil wiring and connector pass, then inspect the controller board - if the coil drive switching device (probably a transistor for a high-frequency induction system) runs hot, it may cause thermal fatigue in the solder on the bottom of the board, leading to a cracked connection. The repair is to remove the burned solder, polish the affected transistor lead with fine-grade Scotch-Brite abrasive, then resolder with lead-free (i. e., high-temperature) solder. It may be necessary to wrap a short piece of 18 or 20 AWG wire around the transistor lead and bridge it across the pad to the circuit trace going to the coil connector if the board is damaged from the heat.
If both of the power connections on the transistor are overheating, the transistor probably does not have a good thermal connection to its heatsink. In that case, you should remove the transistor, clean up the heat sink transfer grease, put a thin film of new heat transfer grease on the transistor, and remount it. (This is not ordinary grease, it's a compound specially made for the job - you can get it at any electronic supply or computer component supplier). If there is a mica insulator sheet between the transistor and heat sink, carefully clean both sides, and apply the heat transfer compound to both sides of the insulator instead of the transistor. Do not apply too much; you want just enough to make sure there is good thermal contact between the adjoining surfaces. If there is a rubber-like sheet between the transistor and heat sink, but no grease, inspect the sheet for tears or hardening, and do not use grease for reinstallation. You may find that the transistor was not flat up against the heat sink because the lead bends held it away from the mounting surface. In that case, tweak the leads using two pairs of needle nose pliers - one next to transistor case to keep the bend from cracking the seal at the case, and the other to bend the lead.
NOTE: do not touch the gate/base lead (left side lead on most power transistors) with your fingers or a tool unless you are first touching the other two leads to discharge any static electricity buildup. The gate is easily damaged by static electricity from your clothing, even if you can't feel it discharge. Likewise, do not put the transistor on plastic unless it is the anti-static kind. The entire controller board should be considered static-sensitve. Handle it only by the edges; avoid touching the circuitry. If you must remove it, place it component side down on your work surface so static discharges from the work surface won't reach the printed wiring on the board, or use an anti-static work mat.
If these measures do not solve the problem, you may have to replace the controller board.
Jul 03, 2015 |