Help needed to bring Yamaha A-1 back to life

theokalat

Active Member
Help bring my Yamaha A-1 back to life

I recently bought an A-1 off ebay.

Before I bought it, I asked the seller all the usual questions about its cosmetic and working condition. He told me it is perfectly fine and that he uses it everyday.

Only the front cover was broken off but he had the cover stored away and sent it out to me for a future repair if possible.

So I bought it.

It arrived a week later, powered it up and the front lights did not light up. No sound from any of the rear outputs either.

I can hear a slight hum coming from the transformers so I know they at least are getting power.

Initially I thought something simple like a wire came loose during trasnsit.

Removed the covers and checked the 7 fuses it has and all seem good.

Next I did a visual check of all wiring just in case some came loose during rough handling in transit, all checked out ok.

I then checked most circuit boards for cracks, or burnt/cracked components parts, all seem fine.

I have a good multimeter that I can use but I need expert guidance in exactly what to check next to find the source of the problem.

I am not an expert in the theory of electronics, but I am very handy with a soldering iron ( I have fully recapped a ca1000, and cx1/mx1 amps in the past, but they all working to start with)

But for this dead amp I probably need step by step guidance from the AK experts here.

Thanks in advance guys
 
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Did you measure the resistance of the fuses to see that they're OK or did you just eyeball them? Sometimes it's real hard to tell by looking.
 
Make sure that the Disc button is not engaged if you're using any input other than phono. You'll get no sound if you you have that button pressed in for the other inputs. If the lights are out on the buttons, it may be hard to tell if they are in or out.
 
Did you measure the power supply voltage, which should be 35V DC? Measure between the two test point on the top of the PS board. Another cause for no output is a DC problem, in this case the protection circuit will not allow neither the speaker relay nor the pre- and tape out reed-relays to switch.
 
Make sure that the Disc button is not engaged if you're using any input other than phono. You'll get no sound if you you have that button pressed in for the other inputs. If the lights are out on the buttons, it may be hard to tell if they are in or out.

Tried the disc button pushed in and out several times. No luck there either.

Tonight after work i will do the voltage tests and check resistance of fuses as i only looked at them.
Will post results.

I am sure with expert help from this wonderful AK community we .can nail this down eventually and get this beast working again.
 
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Do you hear any relay "clicks" shortly after power on?
 
Post a photo of the top side of the main power supply board--the one with all the caps on it..
 
Only a slight hum noise from transformers can be heard.

The slight hum noise suggests there might be some serious current draw happening somewhere. Blasted outputs comes to mind but I'd be happy if you proved me. wrong. :yes: :thmbsp:
 
Didn't get the chance to test the amp tonight due to last minute work commitments.

Should be ok to test tommorrow I hope and will post results.

Cheers

Theo
 
On the Power Supply C. board (NA07041) ie. main board with all the caps mounted on it. Pull fuse F201 and measure its resistance with a meter.
 
you didn't say -- did you try hitting the "speaker" button as well? if that is in the "off" position now, there will be no click, and the relay will immediately click when it's back "on."
 
you didn't say -- did you try hitting the "speaker" button as well? if that is in the "off" position now, there will be no click, and the relay will immediately click when it's back "on."

Pushed speaker button in and out too. Still no click from relay immediately after switching on power.
 
.

I am not an expert in the theory of electronics, but I am very handy with a soldering iron ( I have fully recapped a ca1000, and cx1/mx1 amps in the past, but they all working

And after you were successful with this job you have sold your meter? Why don't you use it?
 
Hi guys,

I had a chance to do some tests with the DMM as some of you advised in earlier posts.

The results are as follows:

Power supply voltage measured 35 volts +/-0.5 volts

There are 3 fuses on the Power Supply Circuit board (NA07041). They measured as follows with the DMM:

F201 measured resistance 0.4 Ohms
F202 measured resistance 0.5 ohms
F203 measured resistance 0.4 ohms

Checked the disc and speaker buttons on the front by pushing them in and out and turning power on. Nothing.No sound. still no lights on the front either.

Used the DMM to see if there was any current to the 3 front lights. No current there either.

Where to from here?

2 photos of the main power supply board taken with my phone, as my main digi camera is broken.
 

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And after you were successful with this job you have sold your meter? Why don't you use it?

The cx1 and mx1 were in good working condition to start with. Only recapped them which was quite a simple job that most people handy with a soldering iron and service manual can carry out.

This A-1 is non working, and I have no idea how to diagnose problems.I am not a techie.

That is why forums like this exist, so newbies like me can get step by step guidance from the experts until we (through a process of elimination) get our treasured gear up and running again.

Cheers
 
I see at least two suspected problem caps in the power supply. I would highly reccomend replacing not only the two but all the caps on this board --Elna Silmic II's are a excellent choice.
 

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Take care, the suspicious capacitor close to the two recitfiers, where the shrink tube seems to have come off, it is the one on the left side on the photo Avionic has marked, is a bipolar electrolytic capacitor (C215, 10 Mikrofarad/50Volt)! The one on the right side, C218 is a standard 100 Mikrofarad/16V electrolytic capacitor.
Even without the SM you can do some measurements. On the "Electrolytic Capacitor Circuit Board", which is the large pcb on the bottom, with the A-1 upside down and the front plate facing towards you, measure the voltages at the end of the traces which are clearly labeled (beginning from the front left +50, +35, -35..... 12 V to E). Read the voltages as labeled? (be careful not to produce any shorts). Next go to the left side and measure collector voltage of the output devices at the points labeled AC & CC, should read something like 35V there (again, be extremely careful!).
 
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