Pioneer M-22 Repair/Restoration

[kunsang]

I was quite lucky and got an M-22 in good condition for free. Sadly only the right channel was working and after some testing, the other channel stopped working aswell.
The replacement caps I ordered (Nichicon KZ, FG and VX) have arrived today and I'm about to start recapping.
The output transistors seem to be fine but I didn't check each of them individually.
The images are of the left channel PCB which is a bit bent. I already removed one leaking axial cap.
Is there anything else to watch out for / replace?

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[EchoWars]

I'd be using 105°C caps everywhere, including the axial caps. There are a grand total of two (2) caps in the signal path, and those are nice 3.3uf film caps, so there's no need for so-called 'audio' capacitors...they just aren't up to the job as far as temperature is concerned. The caps should be chosen for their longevity first, which means Panasonic FM or FC, or Nichicon PW or HE.

As far as the axial caps, Digikey sells some from Vishay/BC Components that will last decades.
1000uf 63V - 4249PHBK-ND
470uf 63V - 4247PHBK-ND

That 22uf 160V non-polar electrolytic is a PITA. I believe the last M22 I restored, I used an inexpensive metallized film cap here...something designed for a speaker crossover. Pretty sure I used this one: http://www.parts-express.com/dayton-audio-dmpc-20-20uf-250v-polypropylene-capacitor--027-436

 

[kunsang]

Oh ok, thanks I didn't know that.
I have a full set of audio-grade Nichicons, and I have already replaced the big ones on the left PCB.

So you suggest I should get more durable capacitors and ditch the Nichicons?

 

[kunsang]

I haven't tested the 22uf 160v bipolar cap yet. Can I use an Illinois Capacitor 206PHC250K aswell?

 

[EchoWars]

If you've run the amp for any length of time, you see how hot it runs. I'd be putting in the longest-lasting high-temp caps I could, like those in my first post. I'd also want nice 25-turn Bourns sealed trimpots for bias and offset adjust.

That Illinois Cap would be fine.

 

[kunsang]

Ok, I'm ordering new caps and trimmers from digikey: http://www.digikey.de/short/3tdf97

 

[gvocale]

Hi, I am just restoring an M22 as well. See the photo of my input boards before restoration.

Does those large diodes on the left side of the top board look original to you, or replaced? Seem pretty large, probably they've been replaced before.

Do I need to replace any diode / trimmer / relay or else?

 

[omri617]

Good luck with your work! I really love the M-22 even though never saw or listened to .
Which makes me think - how does the M-22 sound comparing to TOTL pioneer receivers / integrated amps?

 

[slimecity]

To the OP - Second the high temp cap replacement advice. Replacing the trimmers is also essential.

I would do is clean all the molex pins and sockets- these can get dirty. Then put the unit on a DBT with a (say) 150W bulb, then check your DC offset and bias. A loose connection could be preventing power getting to where it should be. You want to be very careful with this amp as the bias runs high.

With the exception of doing the stuff EW recommends above, You want to diagnose why channels arent working generally before doing a fullscale recapping etc.

Interesting to see a couple of M22 posts on here at the same time. These are phenonemal sounding amplifiers once working properly.

 

[gvocale]

Thanks for the tips! Both posts are mine, I think you're referring to this other thread http://audiokarma.org/forums/index.php?threads/pioneer-m22-restoration.789171/#post-10883477

 

[gvocale]

Question for @EchoWars and @kunsang . Which 33000uf caps you used to replace the original Pioneer ones, if you did?

I got these Nichinon from Mouser (http://www.mouser.com/search/ProductDetail.aspx?r=647-LNT1J333MSE), but the lead spacing is a bit tighter and I'm afraid may short if the cap moves... :/

 

[omri617]

Are the diameters the same?

 

[gvocale]

No, the ones I initially got was a little bit smaller. I found another one with the same diameter and same lead spacing from Digikey (mouser didn't have it in stock). The new part is this one https://www.digikey.com/product-detail/en/nichicon/LNT1K333MSE/493-8972-ND/2549067. Just received it and seem it should be the right fit!

 

[darkhawk22]

Good luck on your M-22 restorations. Having restored one myself I can say they are excellent sounding units once restored and the offset is closely matched. I did not replace the larger 33000uf caps just the other internal ones along with the power supply board diodes and metal film capacitors (high heat area).

 

[mshari]

Hello
My little experience in electronics
I have a pioneer amp M22 there is high heat of displacement 850-vr1 vr2 What is the way to adjust it
Thank you

 

[slimecity]

Hello
My little experience in electronics
I have a pioneer amp M22 there is high heat of displacement 850-vr1 vr2 What is the way to adjust it
Thank you

If the amp adjustments are correct and both channels are putting out the same relative "heat" (based on a rough subjective assessment) then chances are your M22 is running fine.

You cant adjust temp on the M22 - you can adjust the speaker offset and bias. This is a class A amp - its supposed to run hot.

Dont attempt to make these adjustments unless you know what you are doing.