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Transformer Newbie Question
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Old 6th March 2018, 04:38 PM   #1
choujijj is offline choujijj  Canada
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Default Transformer Newbie Question

I have an Akai AM-A3 that powers on, but the main amp relay doesn't click, so there's no sound out of the amp whatsover.

I believe I have isolated the problem to the transformer.

Please see the attached pic:

I know the primary coil has continuity (amp turns on, but tested anyway since this transformer was re-tapped to bypass a thermal fuse I think).

I found this post that indicates the following for this amp and transformer:
Quote:
If the AC Primary side is open, check the thermal fuse on the red wire
145* for 120v 130* for 220-240V (it is inside the wiring) If the problem
in on the secondary side the org wires go to Fusable resistors R1 and R2.
They supply the 15 volt supply from bridge D1~D4. Yellow-white-yellow
supply brige D7. +-36 volts. Main supply to amp. blue-black-blue
supply ac to logic board FL. if you need PDF I have that also.
I tested the secondary coil wires:
- Continuity between the orange pair: Shows continuity.
- Continuity between the blue pair: Shows continuity.
However, any of the blue wires also show continuity with the black wire, which I believe is ground. Therefore the transformer is bad?
Attached Images
File Type: jpg P_20180306_122429_vHDR_Auto.jpg (264.3 KB, 187 views)

Last edited by choujijj; 6th March 2018 at 04:45 PM.
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Old 6th March 2018, 04:52 PM   #2
scottjoplin is offline scottjoplin  Wales
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The black wire is a centre tap between the blue wires. There's nothing wrong with the transformer
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Old 6th March 2018, 05:08 PM   #3
choujijj is offline choujijj  Canada
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Quote:
Originally Posted by scottjoplin View Post
The black wire is a centre tap between the blue wires. There's nothing wrong with the transformer
Thanks so much for clarifying that. I'm trying to figured out why the relay won't kick on after turning on the amp. So I'll need to connect the transformer to test the voltages just to make sure.

So if the blue is supposed to be 36V, it should be 36-18-36 (meaning 36volts across the blue wires and 18v between blue and black with opposite phases?
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Old 6th March 2018, 05:20 PM   #4
scottjoplin is offline scottjoplin  Wales
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You're welcome. There will be 36V either side of the centre tap which will be 0V. Does the relay operate at all, does it switch in then out?
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Old 6th March 2018, 05:27 PM   #5
choujijj is offline choujijj  Canada
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Quote:
Originally Posted by scottjoplin View Post
You're welcome. There will be 36V either side of the centre tap which will be 0V. Does the relay operate at all, does it switch in then out?
Thanks again. I really appreciate it.

To answer your question, no, it does not click at all. If I power on the amp, the lights come on but no relay click. Since someone prior to me tapped an alternate point for the yellow (ac live) I figured there's probably a thermal fuse that's blown. So I'm assuming the transformer is the issue. Not sure how much of a change the new tap point could cause in the primary coil. It's right near the beginning of the wire/coil, where it "hooks" on to the plastic support before being coiled.

Got it solder back now and am going to test voltages before connecting it to the amp.
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Old 6th March 2018, 05:34 PM   #6
scottjoplin is offline scottjoplin  Wales
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I'll wait till you've confirmed if its the transformer or not. Service manual is available here Akai AM-A3 - Manual - Stereo Integrated Amplifier - HiFi Engine
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Old 6th March 2018, 05:50 PM   #7
choujijj is offline choujijj  Canada
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Quote:
Originally Posted by scottjoplin View Post
I'll wait till you've confirmed if its the transformer or not. Service manual is available here Akai AM-A3 - Manual - Stereo Integrated Amplifier - HiFi Engine
I have the service manual, but for the life of me I couldn't figure out what voltages it wants where. Was trying to understand the 7 pins that the transformer's 5 wires connects to.

I just tested the transformer with my multimeter.

The Orange pair reads 3v AC
Blue -> Blue reads 64.4v AC
Either Blue wire to Black reads 32v AC.

The 3V is a far cry from 15V.
Not sure if the 32V is enough for 36V requirement.

Last edited by choujijj; 6th March 2018 at 05:58 PM.
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Old 6th March 2018, 06:06 PM   #8
scottjoplin is offline scottjoplin  Wales
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It looks like the low voltage supply is just for the bar graph display. The DC is greater than the AC after rectification. Are there fuses after the secondary are they ok? Check you have DC after the rectifier
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Old 6th March 2018, 06:20 PM   #9
choujijj is offline choujijj  Canada
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Quote:
Originally Posted by scottjoplin View Post
It looks like the low voltage supply is just for the bar graph display. The DC is greater than the AC after rectification. Are there fuses after the secondary are they ok? Check you have DC after the rectifier

Ok. I checked the secondary fuses for continuity and they had tested fine. But let me put the transformer back together and check the rectifier. Will be about 30 mins or so.
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Old 6th March 2018, 06:23 PM   #10
scottjoplin is offline scottjoplin  Wales
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Ok. The only relay I can see is the output/speaker protection relay
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