Yamaha M-45 cleanup/tuneup

whitrzac

Active Member
1st post, first time attempting to 'restore' an older piece of audio equipment. I'm fairly experienced with car amps/head units, but not home audio gear.


I picked up a M-45 amp on CL a few days ago for $80. All original, including dust from the 80s...

I did a quick test and both channels work as expected, so no troubleshooting to do.

Non of the caps are visibly leaking or bulged. Lots of excess flux that I already cleaned off.


At one point in it's life it was used in a humid environment. There's light corrosion on the jumper wires and some component leads that's not cleaning off with isopropyl alcohol. Is there anything that will clean it off?


There's some heavy rust on the transformer. What's the best method for cleaning it?

Do the power/audio transistors need to be isolated from the heatsink? I was planing on replacing the thermal pads with some decent paste.

Is there anything in particular I should watch out for?


30 year old dust is a PIA to clean off.:no:


It's always nice that yamaha has stuck with the same style, it looks right at home next to my RX-A2020:yes:
 
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First off "Welcome to AK!"

Second, you did good by getting that Yamaha M-45 amplifier for $80 bucks.

As for removing the rust and other stuff that you are asking about, I really can't offer the best way to handle that but I am sure others will be chiming in shortly with their expert guidance, suggestions, opinions, etc. so just keep checking and search here in AK? You'll be surprised at what you can find that can help you out?!

Good Luck!
 
Are you sure that's rust on the transformer, and not the lacquer? Pics if you can.

Some is rust, some is lacquer.

sorry for the crappy cell phone pics... And even crappyer angles. There's some rust on the left side of the transformer. The copper is slightly corroded too.
20140718_191255_HDR_zps28742329.jpg

20140718_191226_HDR_zpsd0b5cbff.jpg

20140718_191217_HDR_zpsbe847eab.jpg
 
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Do the power/audio transistors need to be isolated from the heatsink? I was planing on replacing the thermal pads with some decent paste.
Yes. They need to be insulated with mica insulators. The metal transistor collector tabs have rail voltage on them under normal operating conditions. New thermal paste is reccomended on both sides of the mica.
There's light corrosion on the jumper wires and some component leads that's not cleaning off with isopropyl alcohol. Is there anything that will clean it off?

Replace the components ! I have and M-80 that the entire main board will eventually be 99% new components due to massive corrosion .Most likely cat piss , dust and hair.

There are a couple medium sized caps on the main board, close to the mid center 1000µf/80v I think. They usually have brownish dried glue around the base. If yours has this, anything metallic that this glue touches will most likely have heavy corrosion.
Make sure all traces of this old glue has been removed.
 
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Yes. They need to be insulated with mica insulators. The metal transistor collector tabs have rail voltage on them under normal operating conditions. New thermal paste is reccomended on both sides of the mica.


Replace the components ! I have and M-80 that the entire main board will eventually be 99% new components due to massive corrosion .Most likely cat piss , dust and hair.

There are a couple medium sized caps on the main board, close to the mid center 1000µf/80v I think. They usually have brownish dried glue around the base. If yours has this, anything metallic that this glue touches will most likely have heavy corrosion.
Make sure all traces of this old glue has been removed.


All of the corroded parts are around the glue... There are 5-6 resistors and a couple jumpers that are bad.


There were no mica isolators under the transistors, only bluish green gap pads. I have a few that will work, but not enough to do the whole amp.
What size do I need?
http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=mica+insulator&_sop=15
 
All of the corroded parts are around the glue... There are 5-6 resistors and a couple jumpers that are bad.


There were no mica isolators under the transistors, only bluish green gap pads. I have a few that will work, but not enough to do the whole amp.
What size do I need?
http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=mica+insulator&_sop=15

Blue-green gap pads (Kapton sheets). Serves the same purpose as mica. Where are you going to order your parts from. I reccomend either Mouser or Digikey.You can get the mica's there. You need pads for the TO-3P case style transistors.

I lied. Digikey and Mouser are zero balance for mica.. Ebay probably best bet for low cost bulk amounts of mica from china. MCM,Newark or Allied electronics may also have them.
 
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Nothing at digikey...

Amazon 3rd party has them in the usa.

Now I wait.

More questions: Will this amp run 2 2ohm speakers? There aren't any RMS power ratings for 2ohm, but it has a dynamic rating:saywhat:I'm planing on using it as a sub amp for my HT. I was going to use 1 DVC 4ohm sub, but I have matching sub laying around...

Is there an internal 9-12v source I can tap for a 220mm case fan? <0.5a
 
I have a supply of resistors. I shouldn't need to order any.
The resistors standing upright are fusible resistors. These need to be replaced with either fusibles or flameproof metal film of the same resistance and wattage.

Use regular white thermal compound.Thermally conductive only, not electrically conductive like some of that CPU compound.

As far as pushing a 2 Ω load. I wouldn't.


Check the schematic for fan power source.Possibly off the lamp circuit.
 
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I have some good silicone based past that i use for car amps.

I replaced the fusable resistors with the 'next size up' (1/2w?) that I pulled from another amp. Not ideal, but it will work.


I havent seen a cunductive cunductive thermal past in 10 years. AS5 is slightly capacitive.
 
The resistors standing upright are fusible resistors. These need to be replaced with either fusibles or flameproof metal film of the same resistance and wattage.

Use regular white thermal compound.Thermally conductive only, not electrically conductive like some of that CPU compound.

As far as pushing a 2 Ω load. I wouldn't.


Check the schematic for fan power source.Possibly off the lamp circuit.

Do you use a specific brand of thermal compound, avionic?
 
Most of the nastiness on the transformer is lacquer.

I'm guessing that the transformer was overheated at some point?

No.. Yamaha used liberal amounts of a hot dip type of laquer. When it ages, it just looks overheated.
 
Mica insulators should be here soon...


It looks like I'll need to order more right away too. I just picked up a mx-600 for $100:banana:
 
All back together with a fresh coat of paint...:banana:


The 2 bulbs for the meter are dead. Recommended replacements? I want to match the modern 'white' yamaha displays, if possible.
 
Contact Dave at dgwojo.com. Tell him what you need it for. He can kit you up with 2 incandescent 8 volt/150ma lamps
with pigtails.:thmbsp:
 
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