transformer non-auto

This is not a transformer for automotive use but for my Denon amp that died yesterday. I hope it is not against the rules to ask such a question here. I realise it has to do with voltate and hope it is ok to ask.

The main fuse blew off. I replaced the fuse and the new fuse burst as well, so I decided to be more invasive. I removed the transformer from my receiver by unsoldering all the pins from the two circuit boards. QUestion is what is the approximate resistance I must see on the primary (120 V) side? It shows me about 1.2 ohms now. Is that almost shorted or normal? In the past, I always saw transformers get cut rather than shorted.

Thanks,

Mark

Well first of all, the primary side of that transformer will NEVER see 120v. It is a switched 12 volts DC. A high frequency switched DC. Also, a 120v, low frequency transformer will use a laminated core, where the transformer in a high frequency DC-DC switching power supply will contain a ferrite core, and they are not interchangeable. The DC resistance will very likely be really low, as you describe, but the inductance will be VERY high, at the frequencies the power supply runs.

A power amplifier's DC-DC switching power supply is VERY different than you are thinking, it requires specialized tools to test it, and while I applaud your itrepidity, in trying to service it yourself (this is the way we all learn - curiosity), I think it's time you send the amp out for service, it seems you don't understand enough about the functioning of the power supplies yet.

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

haemphyst, I appreciate your reply but not your non constructive criticism. First off, you say "it seems you don't understand enough about the functioning of the power supplies yet". I owned a shop about 15 years ago where I used to repair TVs and VCRs and hired four employees to do the same at my shop. I do not want point out where you are wrong but the primary of a mains transformer MUST see 120 Volts or the line voltage (near about 110V to be more exact). And secondly a transformer NEVER uses DC. Tansformers ALWAYS step up or step down AC voltage. Since this discussion is not solving my issue, I think I will not waste more time arguing your points. But please do not jump at conclusions and start accusing anyone in the future when you aren't sure. ALso for your information, I have already ordered and received the transformer from an authorized dealer for $120 and my Denon player works perfectly now.

I stand corrected. I re-read your post, and I apologize, and you DID say non-automotive. I jumped to a conclusion, also. I didn't feel I was being particularly rude, though. You are correct, the primary side, in a HOME application, as you described, IS 120v AC, but in a car amplifier, the primary side absolutely is 12v DC, a high frequency pulsed 12v DC. There is NO AC in a car amplifier, until the output stages.

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."