Testing transformers MC30
- Thread starter paulram
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RShackleford
Active Member
Some more info ... like, are they in-situ or in-vivo (in an amplifier, and if so, in what state is it, or just the transformer alone) ? I would think the first step might be to check for continuity in the windings, though I don't even know if open (rather than short) is the usual failure mode. Sorry, not much help.
open wont hurt anything
Power Xformer---check the primary for continuity and against chassis ground, should be isolated from chassis ground. Remove rectifier tube and check secondary continuity and isolation from both sides of primary and chassis (xformer metal) ground.
On the filament side, check secondary for continuity and isolation from both high V secondary and primary.
This checks the no-load condition
As long as your fuse is installed and correct, you should have no trouble, You can use a variac to bring it up slowly and listen for excessive hum--
Its a bit harder to check under load but I would say if no-load is good, under load usually is too.
Output xformer - same thing checking continuity on each side and isolation from other side
Power Xformer---check the primary for continuity and against chassis ground, should be isolated from chassis ground. Remove rectifier tube and check secondary continuity and isolation from both sides of primary and chassis (xformer metal) ground.
On the filament side, check secondary for continuity and isolation from both high V secondary and primary.
This checks the no-load condition
As long as your fuse is installed and correct, you should have no trouble, You can use a variac to bring it up slowly and listen for excessive hum--
Its a bit harder to check under load but I would say if no-load is good, under load usually is too.
Output xformer - same thing checking continuity on each side and isolation from other side
clinic-audio
all on YAMAHA untill 1990
Hello !
Sorry but you talk about power transformer or output transformer ??
Sorry but you talk about power transformer or output transformer ??
Power transformer you can do the resistance checks mentioned above, and then power it up through a 25w bulb in a dimbulb tester. The lamp should be very dim if the transformer has no internal shorts with no tubes or other loads installed, and the output voltages should be a little higher than normal. If that checks OK, the transformer is about as tested as it gets without having a hipot tester to check the insulation between windings.
paulram
Super Member
Hi Clinic -audio. I was thinking both , power and audio and gadget thanks for the suggestion . Actually I have a poor mans variac ready to go! I will be on my second build and unlike the first I did , this second one is unknown to me and would hate to remove and replace components only to find that the trannies have issues.
