Yamaha A-1 JDM ( Silver face ) restoration .

[Nashou66]

I got this and a couple other A-1's to restore and decided to start on the JDM version as its not as common here in the USA.

Powered up with a Step Down transformer . Power switches latching is intermittent and needs to be addressed , I have done this before and have a video on youtube documenting it.
Relay clicks and I have sound from the AUX input from my iPhone. So that is a good start.

I'll start with the PS board .

Here are some pics.

Main PCB need some cleaning for sure.

I have A couple Relays to replace the old one in there .

It has been 5 years since I did one of these , So any tips would be appreciated or other ideas I may
do would be great.


Athanasios

 

[avionic]

Did it have the flip down panel ?Or is it MIA ?

 

[Nashou66]

Did it have the flip down panel ?Or is it MIA ?

I have the flip down panel. But a couple years ago I had a stack of equipment on not so sturdy footing and one night while sleeping
I was awoken by a crash coming from the basement. That stack fell over, a B2 was in the pile!! thanks God that was on the bottom.
The JDM A1 was on top and the door broke off and it was the door side hinge that broke !! I have the pieces and hope to repair it, The side panel bent a bit as well right where the door connects. You can sort of see it in the first pic.

Athanasios

 

[avionic]

I have the flip down panel. But a couple years ago I had a stack of equipment on not so sturdy footing and one night while sleeping
I was awoken by a crash coming from the basement. That stack fell over, a B2 was in the pile!! thanks God that was on the bottom.
The JDM A1 was on top and the door broke off and it was the door side hinge that broke !! I have the pieces and hope to repair it, The side panel bent a bit as well right where the door connects. You can sort of see it in the first pic.

Athanasios

Somebody here on AK is laser printing new hinges.

 

[Nashou66]

Somebody here on AK is laser printing new hinges.

Yeah not the door side tho, I dint think.

I have a bunch of the amp side ones.

The person who sent me the STL file I need to contact to see if he's up to making the door side hinge as well.

Athanasios

 

[mbz]

Reminder that the main caps hold their voltage for a while so bleed with 100-1kohm resistor.

Being mostly direct coupled complicates troubleshooting so ensure that it's working normal before changing out parts, especially in the bias area, also the JDM versions only have the 2 bias transistors where the exports use a "pair" per channel as per the schematic.


Plenty of good test points, well laid out for troubleshooting, just a PITA... mine is still sitting in the corner, will follow with interest.

EDIT: I use a variac, voltages at variac power up are somewhat frightening, eg, dc offset 20Vdc or so

 

[Nashou66]

Reminder that the main caps hold their voltage for a while so bleed with 100-1kohm resistor.

Being mostly direct coupled complicates troubleshooting so ensure that it's working normal before changing out parts, especially in the bias area, also the JDM versions only have the 2 bias transistors where the exports use a "pair" per channel as per the schematic.
View attachment 2451763

Plenty of good test points, well laid out for troubleshooting, just a PITA... mine is still sitting in the corner, will follow with interest.

EDIT: I use a variac, voltages at variac power up are somewhat frightening, eg, dc offset 20Vdc or so

Yep did work an 2 of these before but USA market.

Been lazy lately but I need to get these restored then decide if I am going to sell or keep

Nashou

 

[Asmodeus2112]

I got this and a couple other A-1's to restore and decided to start on the JDM version as its not as common here in the USA.

Powered up with a Step Down transformer . Power switches latching is intermittent and needs to be addressed , I have done this before and have a video on youtube documenting it.
Relay clicks and I have sound from the AUX input from my iPhone. So that is a good start.

I'll start with the PS board .

Athanasios

Awesome! Please share as much as reasonable. I have two A-1's that I want to restore.

 

[Nashou66]

Awesome! Please share as much as reasonable. I have two A-1's that I want to restore.

Will do I had another thread or two on here regarding the first A1 I rebuilt. But that now needs attention again, some scratchiness needs to be addressed, most likely the Disc switch.

nashou

 

[Nashou66]

Well I decided to start with a tear down and removal of the boards. I decided to go straight to the hardest ones, under the face plate. And glad I did as when you go that route I realized I wont have to remove all of the pins on the main Cap board.

Found some damage as well that wasn't from the drop I had. some one was in there before trying to do who knows what.

The Damage is near the volume control, my drop was on the other side of the faceplate near the power switch.

And the main switch board has a crack in the PCB from what ever happened before .

Athanasios

 

[Nashou66]

First you have to remove all the metal faceplate pieces and sub faceplate pieces. This will expose all the switches and
pots. Also some of the switches are on smaller boards and secured separately to the face plate sub faceplate. Remove all those screws as well.

Main sub faceplate removed

Smaller sub faceplate under main one that was already removed.

I started with the speaker mute switch and volume board as they are connected with a three wire harness to a 3 pole header that I removed off the volume board.

Speaker mute switch , if you follow the three wire harness with the red ,white and black wires it goes to the volume board.
Desolder the harness at the volume board. The volume board comes out with some multi wire plugs removed and three
plug in harness's also removed.

At the volume board and connected Disc board the harness wire colors change as the black wire from the speaker switch board
goes to another header with another black wire( GND) Here is the harness on the Disc section of the volume/disc assembly.
The red , white, and pink wire harness connect tot he speaker mute switch board, remove it here. These are for the lights.

Here it is removed from the smaller Disc board

Athanasios

 

[Nashou66]

Next I removed the tone board and head phone board.

Here remove the headers again and the red wire harness at the Switch board side where the header is.
Its easier to remove all connecting wires where they are wire wrapped to a header instead of the other end where they are board soldered. Keeping them all together on a header will make re assembly much easier.
So carefully look for how each board is connected to each other and and find all the headers and remove those.

Here are the red and white wire assembly's that you need to desolder on the switch board, these goes to the tone board

Here is the other header right on the tone board that needs to be desoldered . Its the 3 wire one above the ceramic resistors.
the two wire harness to the left will be removed from the switch board as its blocked on the tone board by a metal shield .

Here is the tone board( one on bottom of pic) removed where you can see the red and white wire assemblies still attached , the 3 wire header removed and the 2 wire header still on board with its red and white wires that went to the switch board.

Athanasios

 

[Nashou66]

Last was the switch board.

remove plugs #2 and #3

And #1

Remove the two RCA's

Then there are three wire assemblies connected to headers, blue, red and grey. Desolder all three.

There are two other headers, one with a yellow and the other with black GND wires.
You can see the open solder holes to the right of the silver boxed relay.

And here is the switch board removed. I think I mentioned all the connectors/wires that needed to be removed.
There are three screws that hold it to the main chassis I believe.

Thats it for tonight.

 

[Nashou66]

Tonight I did a little more dismantling, the Driver board.
There are three sections of wire wound headers that need to be removed.
Dont be alarmed if the wire posts move individually in the headers as you de solder.
The clear plastic is brittle and tends to break. So take a picture of the wire locations/colors
so reassembly isn't frustrating.

The board comes out from the bottom.

Here you see the easily broken brittle header .

Middle header

Right side headers

And the board removed.

Be careful with the larger caps on the Main board. Even tho I thought i had them discharged they still had about 2 VDC. when removing the left side header that broke apart the earth wire swung down and hit the PCB and sparked. Hopefully nothing was damaged .

Athanasios

 

[Nashou66]

Any one have the JDM schematic or board layouts? The Volume/Switch board? MC head amp board shows 8 transistors on the board lay out but on my board there are 16 .

Unless the USA model is the same. Any one have a pic of this board from a USA model? Don't want to open up one of mine.

Athanasios

 

[Nashou66]

I went ahead and removed the output transistors and their associated heat sinks.

Here is the location of the transistor wires that connect it to the 'lytic board. Take a pic and desolder them all.

Now that the transistor wires are desoldered from the 'Lytic board you can remove the 4 screws that hold the heatsink/transistor assembly from the chassis.

Here is the bottom of the 'Lytic board with the heat sink assemblies removed.

There are two transistors that are pressed against the heat sink assemblies , I believe these are the bias transistors.
on mine looks like one was replaced as the rounded side was up against the heat sink. IIRC they should both be flat on that side.
I need to investigate that and see if I can maybe find a better replacement or maybe add insulation to the legs and do some leg work
and flip it around so the flat side can be pressed to the heat sink.

Here they are

Top side of the 'Lytic board with heat sinks removed

Bottom of board cleaned up.

I then removed the bottom metal plate shield from the tone board to address the loose transistor I found earlier.

Here is a pic of the broken solder joints. I will reflow the entire board once I get the few caps for it.

Athanasios

 

[Nashou66]

Did some more work last night and today.

That tone board really needs every solder point reflowed AND solder added. I would say 70% of the joints hardly had any solder .
50% of the transistors where loose, the two 22uf caps also were loose . As I heated the solder points you could see the solder get sucked into the hole
and leave an opening, hence the need for more solder.

The driver board I only changed the trim pots.

I first removed the existing pots and measure the left side terminal to the wiper and made note of that reading.

I then aligned the new trim Pot as it would go in the board and connected my DMM to the left leg and the wiper( same as the original trimmer) and
dialed in the same reading as the original that was removed .

Both replaced

There are mostly carbon filter resistors and I was going to go with all metal film 1% but figured it might change the sound too much. So on this build I am not going to.
But on one of my other A-1's ( USA versions ) I might go for it.

On the pre amp board I decided to remove the MM/MC switch and have a looksey indie to see what might be going on with all of the switches. This one also would stick a little.
So I figured Id clean it up lube it with D5 and hope it worked out the kink.

Upon removing it the one solder bad broke off, this was even using my Hako 805 de soldering gun.

I'll address that after I take the switch apart.

Yep, just as I imagined, oxidation !!!!

The inside of the switch didn't look to bad. And i did want to attempt removing the lid so I just sprayed D5 in there and cleaned the spring
fingers on the switch shaft and worked it back and forth .

Well the switch was still sticking and I didn't want to chance it that it might stay stuck one way or another. So I happen to have some C&K switches that
have gold contacts. So in this spot where the MC signal goes through it I think its a good choice.

One issue I had tho was the switch carrier that is for th the ALP switches is narrower longitudinally . so they wouldn't fit right.
I had to trim the slots wider that the switch uses to slide into the carrier, and then also some on the front and back of that area.
I forgot to take pics as I was annoyed but I got it to slide on and fit.

Pic of old switch and new C&K switch . You can see the slots I am talking about on the old switch easier than the new one. But I had to make that front part of the body on the black switch as narrow and the
grey switch so that it would slide onto the carrier. It needed, I would say, about 1.5mm triming all together. A little from the front slot and back slot. And the same amount from the front and back bottom of that front section.
If you have to do it you'll see what I am talking about once you get in there. Not sure if Alps make the same switches anymore. I like the C&K switches as they have a more firm feel when depressing them.

Here is the repair on the PCB from the lifted through hole pad. I scratched the trace to expose the copper and flowed solder from the pin tot he trace.

Not wanting to damage the PCB any more I decided to take part the other switches on the board and spray D5 anthem and re instal the shaft with the finger springs and work them a bunch of times.

you need to bend back the carriers switch hold down fingers, there are 4 on each switch.

And the switch opened up, flip it over when you remove the shaft as the spring clips might or will fall out of the shaft.

Now spray DeOxit 5 into the switch where the contact blades are and reinstall the shaft flipping the board over again bottom of PCB facing up.
It takes finesse and patience to re insert the shaft with out bending the finger springs. So TAKE YOUR TIME.

Do this to all switches, the source selector switches are a little more involved as they have a toggle feature that connects
all three source switches together. You have to hold the connecting arm to one side so the shaft can be pulled out. Re-inserting will need the same procedure.


Spraying D5 into switch.

I guess if you wanted you could replace all the switches with C&K and get their carrier for them. Not sure if they have the proper
switch spacing though. I will investigate and report if its possible. then you could use all gold switches with will oxidize much more slowly or not at all.

there are only 4, 1 uf caps on this board, those have been replaced.

thats it for tonight.

Athanasios

 

[Nashou66]

While waiting for the 470uf caps to be delivered for the PS I started to get to work on it as Im having a fun time working on this.

On previous A-1's the two transistors that lay flat on some heat sinks were loose and on this JDM model it was the same.
Also on previous PS's the board was darker under the heat sinks, same on this. I found that they did not use enough thermal
paste on the transistors.
So i removed them so I could check the paste situation. Yep not applied correctly. Only on the bottom half of transistors
had paste, the top half close tot he holes were bare.

Here you can see what I posted above, minimal paste and burnt board.

I applied new paste and re installed the transistors nice and tight.Not too much paste so it squeezes out, apply it to fully cover the entire
surface area with a thin coat.

Many of the caps were out of spec except for the 470uf 63 vdc ones. But I got new ones coming in so I may as well use them.

For example the purple 100uf 16 VDC cap was way way off spec. I replaced it with some OsCon caps I had, 20 VDC version.

Only 39uf !!!!! Suppose to be 100uf !!!
Large voltage loss as well. Not good !!!

New OsCon cap specs. Much better and great voltage loss spec !!!
The circuit here will get all the correct voltage it needs.

Here is the partial finished board, waiting on the 470uf caps and the 2.2kohm trim pot.

Athanasios

 

[Nashou66]

I cant find any info on the 1S1815 diodes on the PS. I usually like to use Soft recovery diodes when ever possible.

Any of the experts know what its specs are? Cant find and "real" info on it.

Nashou

 

[avionic]

I cant find any info on the 1S1815 diodes on the PS.

1S1885 D201

1N4007 or equivalent