Help with Marantz 2325 Amp Rebuild

[Ray122]

Hey everyone. Been grappling with the amplifier section of amplifier section of Marantz Model 2325. When I received it, the left channel amplifier was keeping the unit in protection mode. When I disconnected that section and just ran it with the right channel amp, the unit comes out of protection mode and works fine.

Initially looking at the left channel amp I think someone attempted to replace the output transistors, but did it with some parts that didn't look correct, and I also spotted R742 had cracked and broken. After replacing the output transistors with MJ21196Gs and 1195Gs, along with that resistors I had intermittent results, working fine one minute, then lighting up the DBT the next. Clearly the outputs weren't the only problem at large, so to play it safe, I replaced all of the semiconductors in the amp - unfortunately that hasn't seemed to solve the problem either.

Currently Im checking everything with the power transistors out, and what I'm finding is that with all of the new semiconductors I've put in, and while the unit is on the DBT, I'm getting 40V from the output of the amp. Basically +VCC which I can trace all the way back to C704. Otherwise, the voltages everywhere else actually seem to be in line (low because I'm on the DBT, but not above, and in line with what I'd expect.) I believe the issue lies around H704/705 or H706/707. The biggest clue I have is that when I removes H706 and 707, I have 18V on the collectors of H704 and H705, which should only be around 1V. What I can't seem to figure out is why that would be the case when everything else is checking okay.

Anyone have any thoughts on what components I should check next? I'm at a little bit of a loss.

Heres my list of components I've replaced.
H701/702: 2SA722 > KSA992
H703: 2SA722 > KSA992
H704: 2SA720 > KSA1013
H705: 2SC1318 > KSC2690
H706: 2SA818 > KSA1318 (Crossed the collector and base legs to match the pinout of the original)
H707: 2SC1628 > KSC3503 (Crossed the collector and base legs to match the pinout of the original)
H708: 2SC1669 > MJE15032
H709: 2SA839 > MJE15033
H710/713: 2SC945 > KSC945 (Crossed the collector and base legs to match the pinout of the original)
H711/712: 2SA733 > KSA 992
H714/715: 2SC5960 > MJE2436
H716/717: BZ-210 > 1N4747A
H718/H719: VD1122 > 1N4148
H720/H721: 1S2471 > 1N4148

 

[DEFTECHY]

Probably get better or at least more specific help in the marantz sub section of the forum for this.

 

[ivandezande]

Hey everyone. Been grappling with the amplifier section of amplifier section of Marantz Model 2325. When I received it, the left channel amplifier was keeping the unit in protection mode. When I disconnected that section and just ran it with the right channel amp, the unit comes out of protection mode and works fine.

Initially looking at the left channel amp I think someone attempted to replace the output transistors, but did it with some parts that didn't look correct, and I also spotted R742 had cracked and broken. After replacing the output transistors with MJ21196Gs and 1195Gs, along with that resistors I had intermittent results, working fine one minute, then lighting up the DBT the next. Clearly the outputs weren't the only problem at large, so to play it safe, I replaced all of the semiconductors in the amp - unfortunately that hasn't seemed to solve the problem either.

Currently Im checking everything with the power transistors out, and what I'm finding is that with all of the new semiconductors I've put in, and while the unit is on the DBT, I'm getting 40V from the output of the amp. Basically +VCC which I can trace all the way back to C704. Otherwise, the voltages everywhere else actually seem to be in line (low because I'm on the DBT, but not above, and in line with what I'd expect.) I believe the issue lies around H704/705 or H706/707. The biggest clue I have is that when I removes H706 and 707, I have 18V on the collectors of H704 and H705, which should only be around 1V. What I can't seem to figure out is why that would be the case when everything else is checking okay.

Anyone have any thoughts on what components I should check next? I'm at a little bit of a loss.

Heres my list of components I've replaced.
H701/702: 2SA722 > KSA992
H703: 2SA722 > KSA992
H704: 2SA720 > KSA1013
H705: 2SC1318 > KSC2690
H706: 2SA818 > KSA1318 (Crossed the collector and base legs to match the pinout of the original)
H707: 2SC1628 > KSC3503 (Crossed the collector and base legs to match the pinout of the original)
H708: 2SC1669 > MJE15032
H709: 2SA839 > MJE15033
H710/713: 2SC945 > KSC945 (Crossed the collector and base legs to match the pinout of the original)
H711/712: 2SA733 > KSA 992
H714/715: 2SC5960 > MJE2436
H716/717: BZ-210 > 1N4747A
H718/H719: VD1122 > 1N4148
H720/H721: 1S2471 > 1N4148

H714/715 is 2SC496. Should be replaced with MJE243G.
H710/713 should be KSC1815 or get the C version of the 945 so you don't have to do the lead thing.
I'm worried about the MJE drivers, I've had bias and stability issues before. KSC2073 and KSA940 are an option as well.

The good news is that you have a working channel, so I want you to start measuring resistance to ground on all the transistors. Compare that reading to the exact same place on the other channel. You will find the issue. I promise.

Make sure all transistors are installed correctly, that all resistors measure good, and that there's no burnt traces. Check everything around R742 and on the opposite side.

 

[Ray122]

Thanks for the advise! I'll give that a go and report back here with what I find. If I'm still having I'll try reposting this in the marantz sub section.

Either way, really appreciate the insight!

 

[Ray122]

So the past couple nights I've tried measuring resistance to ground on all the transistors, and although I'm finding some discrepancies between the good channel and the bad channel on the collector of H706, base of H708, emitter of H712, collector/base of H714 and collector of H715 - however I've checked everything around that area and still can't seem to find a smoking gun.

I'm going to try moving this post over to the Marantz sub section and see if we can keep the conversation going there.