Pioneer M90 Amplifier Protection Circuit

Time for a full rebuild I would think. Too many components might be at the end of their life. Replace all carbon resistors with quality metal films i.e. Takman. Check plate resistors, too. Noble are unobtainium, Fukushima are too. Mills 5W whats left. For outputs try to get A1962/C5242 Toshibas. They are discontinued already, but you still might get them. Beware of fakes, though.
 
Thanks for coming back! I thought you had left me !!
I found Toshiba c3907, can not I just change broken ones?
I have the Pioneer diagrams but I do not understand: apart from power (1/4 or 1 / 2W), tolerance (J or K) and value (I read it on the schematic of the pcb, the colors could be degraded) how do I decide the type of resistance?
In the Pioneer list are identified with "RD", "RFA", "RS2LMF", "RS1LMF" and "RDR" ...
If I find different transistors such as 2SC2238B, I find 2SC2238 (without B) is a problem apart from an excess of heat and a more rapid degradation (only for the tests, then I replace it!)?
I also found two Noble resistance (2W + 2W 0.47ohm) burnt, are these to change with Mills 5w (5W + 5W 0.47ohm)?
I have to change also PA0016, some pins (11,12,13) are dead!
Excuse me but I need you !!
Thanks for everything!
 
"Dont forget to replace Q115-118 with onsemi A1013/C2383."

Q115 on Power Amp A, replace the a1145
Q118 on Power Amp B, replace the c2705

I have to change pairs, right? Q115 and Q117 on P.Amp A; Q116 and Q118 on P.Amp B

on the transistor A1013 the final "Y" or "O" is important ??
 
I read the two threads, I understood which transistors to change, which diodes and I decided to replace capacitors with quality electrolytic but I have not yet figured out how to choose the resistance model. You use different types I see them (in the parts list) all the same (apart from resistance, power and tolerance). can you help me? thank you
 
Instead of Noble rgc22 2w + 2w, I can use two resistors 0.47 Ohm 5W 5%, 50ppm Resistance ceramic wire wound OHMITE AG Audio Gold? obviously changing them all!
 
Never used AG Audio Gold. I extensively use Ohmite WN and WH series for repair or restoration at power resistor position. For output emitter resistors I use only Vishay Mills MRA. There are many options for board resistor choices. Depends on the money you want to spend. Some of my customers ask for Vishay Z-foils 15-20 USD a pop. Basically, very good results without overspending can be had using Vishay metal films CMF, RN, even PTF (i like those). Very reliable. You can mix in cheap audio resistors like Takman REY. Use 0.5 W ( CMF60, RN60) rating. For power resistors you can use Vishay RS, NS, CPF, WN, WH. And there are gazillion boutique resistors at audio stores. Always check those with ohmmeter before installing. Some are really good like old Shinkoh tants, Caddocks, but many are not worth it. The return is not proportionate for the funds spent. Unless, you populate the whole board with Z-Foils :)
 
:trebon:

thank you so much! I start the search and selection of resistors as your directions! I decided to big all the new power transistors, the 3907 I bought are fake, the replacement is difficult !! now it will take some time to get the components, I will update you as soon as possible! thanks again for the help!
 
Of course they are. You should have posted before sticking them in. Your fakes blew taking out plate resistors and components up to PA0016. The only Toshiba subs you still might get are the discontinued A1962/C5242. The A1942/C5200 are the same internally, and are still produced, but the case is bigger, I do not know if they would fit without modifying heatsinks. Another option is Sanken. Mouser carries A1962/C5242 O grade by OnSemi - that is your best choice. Get them if you cannot get the Toshibas from reputable source. Also get some TO-92 heatsinks, and some quality TO-220 heatsinks like Aavid for your drivers. For outputs use Dow Corning 340 compound, also Arctic Silver Ceramique is ok (a little overkill, though).
 
Hi Guys, I'm back! I waited a while to get all the electronic components suggested by Hennessy and now ... I'm ready!
Today I disassembled AWZ1026 and AWZ1028.
I started the reconstruction from AWZ1028, where power transistors and resistors were burned (even those ceramics!). Disassembled and cleaned, also removing the brown glue is ready to be repopulated. For the moment I keep the original wiring.

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First of all the components ... Unfortunately I did not find any Noble resistors to replace those burned so I opted for OHMITE AG5, easily available, of higher wattage, same resistance (0.47ohm) and not excessive cost.
The other resistances are all Vishay RN or CMF.

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And now the assembly ...
One factor that I have not mistakenly considered during the purchase of resistances is the size! Some resistances I had to mount vertically and for those ceramics I widened the common hole with a Dremel ... I used a little imagination, not elegant but functional!

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The final result is still acceptable ... or am I wrong?

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Now I'm undecided ... The power transistors is better to weld them now or after mounting transistors and board on the chassis? The second option would give me certainty about the distance of the transistor from the pcb but I ask those who have already done this ...
 
Silver-plated MICA capacitors and FILM ... Does it make sense to replace them with new ones if they work? For physical characteristics they should not degrade like electrolytic ones.
What do you think about it?

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Power boards look more less ok. You should mount power transistors first, and solder them to the board later, after installing said board. This prevents stress at the joint. Leave blue film caps in place, they are polypropylene. Not all brown film caps are micas, some are polyester. Micas are ok, but you can replace them with Kemet PFR, Wima FKP2, and similar polypropylenes. C101 replace with 215p Rifa PFE225, C113 with 0.01 PFE225, C107 and C109 with one 20pf Styrene quality cap with voltage rating more than 160V, such as LCR. These are just some examples and suggestions.
 
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