Author Topic: MMV42054BA (Maytag) Runs, no heat - "HVT" fuse blows (wrong type fuse?)  (Read 1434 times)

Offline c-peter5

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   OTR Micro,  blew quickly (there are two fuses)
   Replaced shorted cap w/used - within .02uf, w/ matching diode.
 Days later, low power; "HVT" fuse not full voltage at both ends (weird).
   1 month later; ran, no heat. I removed control panel, tried for at least 5 minutes to heat a coffee, "Main" and "HVT" fuses 120v both ends.
   So I replaced the panel and left for work. Cooking attempts were made, lights/power/display quit. Found "Main" fuse blown.
   Next test, the "HVT" blew in a few seconds.   
  I moved mw to bench and tested using an old Triplett 630-PLK type 6 w/ two batteries (one is 30v), and a Radio Shack 22-221 (analog).
  MAG filament; 0 Ω. Filament to chassis; ∞ (both meters).
  CAP; R/S - 200k to ∞ both ways. Triplett (x100k range) - near 0 to 9000k (both ways). Should go nearer 0? And to ∞, not 9 mega-ohm?
  DIODE; R/S - ∞ both ways. Triplett (x100k range) 85k one way, ∞ other. Should be less than 85k? (wouldn't blow fuse if open though) 
  HVT Filament winding - 0 Ω. Filament to chassis - ∞ (both meters).
  Secondary - R/S; 350Ω, Triplett; 500Ω (mw paper says "Approx. 90Ω).
  Primary; This has three wires at primary; blk, wh, and a blue between them. Apparently the blue's tapped in the middle for "low" power? It goes through the "HV" fuse to a relay that has the other wire white. The paper found in the mw simply says "Primary winding Approx. .3Ω".
  wh/blk; R/S - 0Ω. Triplett - .6 Ω, then trips "protection" button.
  wh/blu; R/S - 0Ω. Triplett - .2 Ω.
  blu/blk; R/S - .5 Ω. Triplett - .5 Ω then trips "protection" button after varying amounts of time from instantly to 10 seconds or more. I tried leaving the R/S meter attached (set to 5vdc - it's lowest range) to see if there was voltage somehow being induced and tripping the protection, and the needle did move a tiny bit.
  The original fuses were "BUSS MDA 20A", replacements were "BUSS ABC 20A", after running out, I'm using 20 amp glass fuses - could it be it just needs the correct "time delay", or "slow blow" fuses?
  Though my ohms readings are mostly "off", online info says testing the HV components is best done by replacing with "known good" parts - are there ways I can run mw with certain things disconnected to pinpoint the problem (without electrocuting myself)?   
  I couldn't find info on the three-wire primary until I searched "inrush relay" (one of three relays shown in schematic). Could I try (for example) disconnecting the primary wires, run cook cycle, then introduce 120v to the black & white or black & blue terminals with a separate cord? Wouldn't this eliminate problems in switches, relays, etc. that occur only under load?
  Any ideas would be appreciated.
« Last Edit: July 27, 2014, 07:56:55 PM by c-peter5 »

Offline Maytag Man 6725

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Wrong type fuse could very well be your problem. Also could be a bad mag, but usually blown fuse is cap related or door switch

Offline c-peter5

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I ordered 5 Buss MDA for $5 on ebay (two ABC's cost $6 at the store), so I'll try that first. All three door switches are reading right (especially checked for closed monitor). Should I buy another cap? Would mag show n/g if I dug it out and had a look-see? (never looked at one before)   

Offline tgoods

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I've seen a blown HV transformer fuse one time and it was a bad transformer. 

Offline c-peter5

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Anyone know if this place is legit;  http://www.wellsappliances.com/store/   They have an HVT listed for $20 new... SHV-U4205A
« Last Edit: July 28, 2014, 09:41:14 AM by c-peter5 »

Offline AJ

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Never heard of them. Any parts you purchase from http://appliancepartspros.com or http://repairclinic.com can be returned for any reason for up to 365 days and they help support our site.  O0
Hope you find our website helpful.

Offline c-peter5

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New MW costs less than HVT! Anyone need some parts? Correct fuse blows a little slower (cooked 5 seconds) than glass one... Can I run with HV wire (and filament) disconnected from mag (no blow; bad mag / blows; bad cap or HVT?), then, if still blowing, disconnect at cap (if still blows; bad HVT / no blow; bad cap and/or diode)? Or can these only be tested under load/by substitution with known good part?   

Offline Maytag Man 6725

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Bad mag

Offline c-peter5

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Finally got money for new magnetron - no help - still blows fuse quickly. I see they're on backorder...

Offline c-peter5

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HVT, that is...

 

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