Is any one familiar with nakamichi pa-7 soft start circuit?
Looking to buy this amp but the seller says pa-7 soft start circuit is blowing fuses but it's ok to by pass this circuit..amp sounds good with circuit bypassed
Would anyone elaborate on it? What could be the root cause
Looking to buy this amp but the seller says pa-7 soft start circuit is blowing fuses but it's ok to by pass this circuit..amp sounds good with circuit bypassed
Would anyone elaborate on it? What could be the root cause
soft start function is enabling to have properly sized mains fuse, not gargantuan
pull his price down, repair it before proper use
pull his price down, repair it before proper use
And the soft start is keeping the on/off switch from arching etc.. PA7 has big transformer and big caps. Definitely have the soft start repaired. I have worked on it before, but can’t say exactly what is/could be wrong. Perhaps the delay circuit is defective, so the relay is activated to soon. Or the fuse burning could be a symptom of something else... Make sure the amp actually works.
Yes the amp works . The seller had it plugged in to his favorite speakers. Bowers and Wilkins 802 I believe. The amp played pretty loud for 30min. Dc leakage at speaker terminals was 2 and 4mV. The seller said same thing. He left the amp on all the time to prevent damage from current surge. Will look into the circuit later. Found some people online with same issue on this amp but no resolution
Get hold of the service manual from Hi Fi Engine (free download) and sort it out - has the schematic, parts list, board layouts and biasing info to check the amp once you get it 100%.
Haven't really opened or read manuals yet. But read in some forums that thermal fuse inside the transformer may be the culprit of a high start up current.
Nakamichi pa-7 has thermal fuse inside the transformer. I could not find any tips on how to check it thermal fuse Is bad inside .
What usually happens to an amplifier with bad thermal fuse in transformer.
What currently happens is that fuses on soft start circuit keep blowing. The tech that worked on this amp before shorted them. And said best to keep the amp on all the time to avoid surges. Here is the thread where a guy opened transformer and replaced thermal fuse
https://www.diyaudio.com/community/...ofuse-in-the-potted-transformer.179155/page-2
Nakamichi pa-7 has thermal fuse inside the transformer. I could not find any tips on how to check it thermal fuse Is bad inside .
What usually happens to an amplifier with bad thermal fuse in transformer.
What currently happens is that fuses on soft start circuit keep blowing. The tech that worked on this amp before shorted them. And said best to keep the amp on all the time to avoid surges. Here is the thread where a guy opened transformer and replaced thermal fuse
https://www.diyaudio.com/community/...ofuse-in-the-potted-transformer.179155/page-2
I am not an electrical engineer. But I guess the amp would not work at all if thermal fuse is open.
If the thermal fuse in the transformer primary winding has failed, you will not get a resistance reading between the two outer primary winding wires. If OK, you will measure resistance. The transformer will be dead if the thermal fuse is open.
If the soft start circuit is bypassed and the mains fuse does not blow, then there is a faulty component in the soft start circuit between active and neutral.
If the soft start circuit is bypassed and the mains fuse does not blow, then there is a faulty component in the soft start circuit between active and neutral.