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Marantz 1152dc transistor replacement

E

EnnioMorric1

New Member
Hello AKers,
I'm actually working on a friend's Marantz 1152dc which had a lot of corrosion caused 30 years ago by cat urine (just... imagine...) and then this amp stayed unused until now. I've made a lot of work on chassis, and fortunately inside the only board that had corrosion problems was the pre amp (PJ00). Traces lifted and oxidized apart, the only problems with components were about a faulty transistor, burnt resistors (R439 & R440 with one of 22-ohms resistor, that seems a pretty common problem on this board related to transistor failing) and a couple of caps to be replaced... I've replaced all electrolytic caps with brand new Nichicons one, i've replaced Q401-402-403-404 (2SA872A) with KSA992, Q405-406 (2SC1775A) with KSC1845, Q407-409 (2SA912) with KSA1013 and Q408-410 (2SC1885) with KSC2383 but i've found out that KSC2383 and KSA1013 won't fit and cause oscillation, bringing back A912 and C1885 did the trick but light noises and pops can be heard on speaker, which amplifies if Phono input is selected.
I think i'm going to replace those 4 transistors (Q407-10) with new ones, i'd like to know if someone knows good replacements which could fit on this configuration, i have to say that the only caps i did not replace are the filter ones (18000 uf) and i've cleaned the relay, hopefully those noise are caused by this 40+ years old transistors and not from those more expansive parts.
Any help would be appreciated, thank you so much i hope you can understand my english as it's not my first language.m1152dcphono.png
 
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Looks like you are putting NPN in place of PNP and vice versa.

"(2SA912) with KSC2383 and Q408-410 (2SC1885) with KSA1013"
 
Skywatcher said:
Looks like you are putting NPN in place of PNP and vice versa.

"(2SA912) with KSC2383 and Q408-410 (2SC1885) with KSA1013"
Click to expand...
Nope, i just mistakely inverted in the writing sorry! 2SA912 with KSA1013 and 2SC1885 with KSC2383.
I edited the typo, and i'm adding a video with the noise from speakers, when the volume is higher is when i switched from AUX to Phono 1
Thank you :)
 
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KSA1013/KSC2383 should be fine in those positions Q407-410. Check all the rest of your resistors because some in that area have been known to drift out of value besides the ones you mentioned.
 
Ceramic caps can go bad as well, especially if there is corrosion and moisture infiltration. One bad one in the wrong place can allow oscillations to develop.
 
Skywatcher said:
Ceramic caps can go bad as well, especially if there is corrosion and moisture infiltration. One bad one in the wrong place can allow oscillations to develop.
Click to expand...
I'm gonna replace ceramic caps, check resistors tomorrow and i'll put back 1013/2383 combination, i'm aware that this transistors could be fake... i'll check everything and eventually report measurements... Thank you Skywatcher for the help, i'll let you know in a couple days (if i'll find caps ready to buy on local shop ofc)
 
Hi @Skywatcher , i had time to change ceramic caps (5,6 pF on 5 pF and 22pF on 20pF, the only different values i've found locally, others ceramic caps replaced matched exactly capacitance) and i put back a1013 & c2383 in Q407-8-9-10 replacing the originals, hadn't had time to check all resistors but there are a couple of things i've noticed:
the transistor i have, a1013 and c2383 imho could be fakes, they heats up till 70 degrees Celsius while originals don't go up more than 45 Celsius.
All ceramic caps were replaced were spot on measurement off board.
Popping noise still present, now seems not depending on volume or balance but i cannot recall if was the same before or not.
I've taken this measurements with a1013 and c2383:

(E-C-B)
- Q407: -43,9V | +0,127V | -44,41V
- Q408: +42,22V | +0,141V | +42,78V
- Q409: -43,77V | -0,02V | -44,25V
- Q410: +42,17V | -0,01V | +42,71V

Voltages accross R439: slowly rises till -1,15V and then stabilize, R440 do the same but at +1,15V.

I think transistors are fakes, i've bought em on ebay but they don't look originals to me and the price i bought them could be an hint too (too low), seems also they suffer from overheating and the sound is muffled and high frequencies are cuted-off intermittently...

I don't know anymore if sound depends on transistors or not, could be a ground issue (for the little knowledge i have), i don't honestly know.
I've seen also KSC2690A and KSA1220A (or TTA004B,Q - TTC004B,Q) as possible sustitutes but they are in different factory form even if they could handle more power (if i'm not mistaken) and match transition frequency (A1013 for example has frequency 1/4 of original A912)...
The noise is not constant, somethimes you will not hear it for minutes then come back and could last many seconds...

Thank you everyone for every help, appreciate so much :)
 
If you want to get components from FleaBay, get them from the seller Affinity for Artifacts, also known as love.peace.and.music. Ben is our very own @EastPoint and everything he sells is the genuine thing. No "fakes" or counterfeits whatsoever.
 
Thank you Skywatcher, unfortunately i'm in Europe and it's not really chep to buy from States... anyway i'm going to find original A1013/C2383 and see if i can find the problem... i've resoldered some joints on the board that seemed to me not good and now the noises are less but still present in Mic/Tuner/Aux, in Phono 1-2 thery are louder and more constant... i've also checked the dc offset that fluctuates a lot on Left channel (JN01 to ground, -15/20 mV to +10 mV) and is pretty stable on Right channel (about -26 mV, haven't set it after swapping transistors)... of course if i switch selector to Phono 1/2 there is no stability at all and the meter always steps OL on the cracking spikes i hear from speakers...
I'm very undecided on choosing transistors cause i don't really want to waste a lot of money ordering all of them... i've also found 2SA912/2SC1885 here in Italy but could be another fake and honestly i think if those went noisy could happen again with these (if originals) NOS... don't really know if those C2690/A1220 would fit on that position...
Any hints would be appreciated, thank you really really much for help! :)
 
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