Pioneer M-90a hit the floor!

[Meteli]

No, seriously it did...
Let's start from the begining.... These are original sale pictures from eBay, all the best amps comes from Italy sold literally on the street, with power cord cut and legs missing.
Oh this is going to be fun, only thing I hoped was, no-one have try to fix it. It was an auction and got it for fair price.

I have zero idea what have hapend, is a earthquake or Donna had enaugh? Bad furniture or move damage, No idea.



(To be continued...)

 

[Meteli]

I gave instructions not to carry parcel in house and I am glad I did, because for my luck no-one had try to do anything to it.
Luckily it was cold during nigh, after blowing dust out I left in back of my car, so all the bugs died.
No, it is not a dead mouse right side between board and cooling.

 

[Meteli]

What title says about hitting something, usually floor of somekind, I was not kidding, if you look first picture, plastics from center leg is there and screw were cut that holds bottom plate. The worst thing is that chassi is compleatly bend and all the parts attached to it.
Axle for volume pot is also gone and pointing wrong dirrection.
Even transistor legs are bend.



Damage have also loosen transistor from larger board,


The worse thing was end transistor board that was compleatly broken in half.

 

[Meteli]

I wanted this M90a to work before I start go deeper, So I found couple of resistors gone blank and only one transistor looking like all options closed. I took caps out 25ohm resistance seems to be norm. Fuses I blow my self accidently and my mistake, they were good.
Strange thing was one relay not engaging other side at all, damage had broken mechanical part inside, so it only drops one side, these are non open versions, cut to see what was it.



Transistor board I epoxy glued back together and used juper wire to connect traces again, no trustin for glue and solder, so now-on it two boards, if they seperate in future, it does not matter.
I drilled exsisting holes bigger or middle of two components for the wire.


And what you know, it works!
Yes, bouble wrap acts as an insulator for 230v and wood chips keeps bords for not touching chassi, but it works!
(See how bend that chassi is upper left in picture.)


Now what?

 

[Meteli]

I can not dress this enaugh, pioneer amps are the worse to repair, not desing to be fixed, amount of wire to clear, even to get any board is devestating and to add to that some boards were so near to be cut that actually removing them from chassi was a challenge.
I did not even try to take out wires from posts, but desoldered post out of the board with wire.



Then you transformers pointing to wrong dirrection, after all they are the heaviest parts and continues to travel after everything else makes a sudden stop, so chassi has to come out.

Front side.
Note that all of the wires have to come out as compleat bundle, with all the small parts with it.

 

[Meteli]

So here is the chassi.
A mount of work to get it out without any components is after many hours.
btw there is a real copper plate under transformers, it is top right in picture leaning.
So I straighten the chassi and manage to make it non rocking and even. No new holes drilled.
I like to work electronic equipment on wool carpet because it leaves no marks on surfaces.

 

[Meteli]

So next is to solder and solder I did!
I change out all the resistors to Vishay MRS25 silent metal film. I mached pairs so other side got identical resistor to same place.
All then electrolytic capacitors and if I could change then to film.
Most of the transistors diodes.
There is only one electrolytic capacitor in signal path
I did not change out ones that drive LED's and visual parts of the amp.
I did leave the Shosin caps and those odd green ball things
And also glued corners back together. Luckily none of the traces were cut and I used nylon washers to screw them back to chassi, so cut parts are only for support for now.


Pre amp section, funny that this amp got it, also got all new parts with relays.


Other side before


After and ready to go with others.

 

[Meteli]

Old Toshiba out and new Toshiba in:


This how they did in factory, screw transistors in and soldered board to it.



Took volume pot out and clean it, oiled it F100 and D100
Before and after in same picture.
It was dry and bad.


Next the fun part.
Yes 22uF caps do fit.
Also new relays. and swapped power to 240V


Axsle joint for volume potentiometer I replaced with clear plastic tubing, seems to work as good.

 

[Meteli]

Next to the front.
Incadence bulbs for powering up, you know yellow and red were both broken. Damage was so violent that even red bulb was gone as it usually just lights up few seconds, it would be odd to burn out.
I swappwd LED's to replace them, now red is in middle and kind opens up to yellow as they swittch.



Next I try to power it up again and nothing... Can't get out of the protection!
After a while I found last damage, wire was almost cut by chassi and grounded, luckily it was something that devise itself found and not burned anything. I changed compleat wire.


Last issue is that one of the lines do not shut of, it is constantly on, I could only thing there is some damage inside gas filled display unit so I desoldered that one line, does not matter.
But now it works.
New power cord, broken screws, new legs are from spare part A-717, those parts are same with Elite series.
Only hatch is missing.


Can you imagine what this amp sounds like with full set of metal film resistors, without any resistor noise?

 

[David Z]

???

 

[Watthour]

That was quite an effort to recover from that kind of damage. Thank you for documenting the repairs.