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Marantz 2275 - Right P700 issue

B

buzzclip

New Member
I picked up a 2275 from an antiques guy last spring for a good price. It'd never been restored but still powered up and sounded okay. I upgraded the lights and cleaned all the pots first thing and had a beautiful summer and fall blasting records. The right channel would drop out at really low volumes and I wanted to fix that eventually. I bought a restoration kit with Silmics from irebuildmarantz.com, but was dragging my feet on starting. Then an output transistor blew, the relay wouldn't click, and I wasn't getting any sound. It was time.

I've never done this before, but I had the time and willingness and a decent aptitude for learning new skills. It was going pretty smoothly. I recapped the power supply, phono amp, pre/tone amp, and both right and left main amps. The new relay was clicking. I regret not testing with speakers every step of the process, but the space where I was working and how my speakers were mounted and wired made it difficult. I still felt pretty confident that it would work and was biasing as a last step before hooking the receiver back up. And then it all went wrong.

Two mistakes -- I didn't have a dim bulb tester and I didn't have alligator clips for my MM. So I'm trying to bias using the probes like chopsticks on J703 and J704 and adjusting the potentiometer with my left hand and POP! I shorted it out. So disappointing after all that work. The fuse was blown, the resistor at R735 was cracked in half, and I figured I probably blew the output transistors again. I ordered new parts and spent the waiting time combing through tons of AK posts and watching relevant videos on Youtube and building a much-needed dim bulb tester.

I finally got the parts today. I had a little trouble finding the right resistor. I think they're more common for carbon with those specs (100ohms, 5% at 1/2W). But the original ones were blue (metal film, right?) so I got a metal film replacement with the same specs from Mouser. The replacement is 1/10th of the size. I double-checked and the specs are right, but it's so much smaller. Is normal when replacing 40 year old resistors? The size of the resistor makes me suspect this might be my problem.

I replaced that resistor with the tiny one and the output transistors with new mica some heat sink compound and powered everything back up. No relay click. I tried plugging the left channel into the right wiring harness and vice versa since the boards are identical. I always get the click with the left but never the right. I think that isolates it to this right P700. I'm not sure where to go from here. Visually I don't see any issue with components. I'm down to test everything but haven't found much information on how to test circuit board components in a Marantz. Also, I only have a MM and not an ESR meter. I'm not sure if I want to invest in an ESR if this is my only project. Is there anyway to go about it? Any videos you can recommend on how to test resistors, transistors, capacitors? Are there components that are most likely to short on the P700 to check as a starting point?

According to the threads, similar thing happened to Dr. Humboldt in 2016 on his 2275, except his fuse kept blowing and mine is stable after being replaced. He sent his unit to Bob (wlhd1610), who is based not far from me in Upstate NY and would be perfect. But it looks like Bob hasn't been active since October and members haven't been able to get in touch with him. I hope he's okay.

I've really enjoyed the work, especially when it was going smoothly. I'd love to finish the work on my own but am willing to bring it in to a professional at this point. Does anyone know any other Marantz experts in Upstate NY or NYC? I tried Hudson Valley Hi-Fi, but the guy there sounded appalled that I did any recapping on my own. I'm humbled by this situation and embarrassed by my negligence. I really just want to play my records again. Open to any advice for the DIY route or professional recommendations. Thanks!
 
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Bob Speece has moved out of state, and has not been heard from in months. As for the unit, don’t power it back up without a DBT. Diagnosis will involve tedious pulling of transistors and testing, then replacing if good. You can test with a DMM with diode test function per this thread:

https://audiokarma.org/forums/index.php?threads/bipolar-junction-transistor-testing-basics.43186/
Then diodes, then testing of resistors in-circuit, and pulling those that are way out of spec and testing again. Most will test in spec after pulling. You are looking for open or shorted semiconductors or open resistors. Last on the list is caps, but unlikely if not visibly blown up. If this would be above your capabilities, look for a good tech. But Bob is unavailable at this point.
 
Thanks, Steven. I appreciate the advice and that thread is super helpful. It's also good to know what order these things are most likely to fail. I'm almost wondering if I'm going to be pulling out all those transistors and resistors, I might as well just replace them all. I didn't realize those components were so cheap individually. It would be tedious buying all the right components but so would pulling and testing everything. I'm still weighing out what to do and may have a lead on a tech in NYC. Hoping I can get the unit up and running soon.
 
There are different philosophies on wholesale transistor replacement. I don’t do it because almost all transistors from that era have to be replaced with a suitable equivalent. But many small changes are likely to change the sound. I change known troublemakers and anything that tests bad. I usually also replace diff pairs on amp boards. The rest, I put back if they test good.
 
I wanted to follow up with this as I’m still having issues. After struggling with the the right channel, I found a tech in NYC and brought the unit in. He found a shorted transistor (one of the square plastic ones) and it was working when I picked it up. He asked why I didn’t change the filter capacitors that came with my restoration kit from IRebuildMarantz. So before hooking it up at my house, I changed the filter caps. When I hooked it up, the left channel was out. The relay was clicking but the channel was distorted. I thought I’d messed up soldering the wires to the caps. I tried a few times with Randy’s advice and struck out.

So I brought the unit back to the tech. He cleaned up my job on the filter caps and kept testing the board. He changed a few things but said it was ultimately the output transistors, which seem to be the most delicate. Anyway, I paid another $260 and took my unit home.

I hooked it up to two sets of speakers (main and remote for separate rooms) and switched the input to phono. Immediately the left channel was distorted again and I smelled burning. I opened the unit up and the resistor at R734 was burnt out. The tech changed it but used a carbon-film instead of metal-film resistor (not sure if that makes a difference). I had a spare and replaced it. I also tested the output transistors and one appeared to be shorted, but the multimeter tests for transistors is always a little vague to me. I put it in anyway just to see and turned on the unit with a DBT. The bulb started pulsing and the smoke appeared at R734 again. I unplugged it promptly. I’ve got a lot of questions.

Why would the unit work in the tech’s workshop but not my home? Does it have anything to do with me plugging speakers into both the main and remote terminals? Is it possible that the voltage from my outlets are playing any part? The tech had the unit plugged into a plug that monitors the voltage in his shop. Seems like the output transistors are always short when there’s a problem with the power amps. Are they commonly so delicate? Should I expect that the tech will fix this since the results are unsatisfactory or will I have to pay to have it serviced all over again? Lastly, any ideas on how I might fix this in case I attempt it to do it myself?

Thanks.
 
You aren’t running two sets of 4 ohm speakers are you? That could sure do it. Even one set of 8 ohm and one set of 4 ohm speakers, if run at the same time, could blow outputs.
 
They should both be 8 ohms. I’ve got a set of early KLH Sixes in the living room and a set of B+W DM1200s in the kitchen. They both worked fine on the 2275 for the first six months. And they’re both working on a newer Yamaha R-S700.
 
If they are both 8 ohms, it should be able to handle that. You probably still have one or more components way out of spec or blown. It takes a lot of testing of components, but I pull every transistor one at a time and use the 6-way diode test looking for a shorted transistor. I put them back if they test good. Then I test diodes and resistors in circuit, and raise one leg to retest out of circuit if they don’t test within spec in circuit. Of course, you have to scan the solder side with magnification looking for solder bridges or cold solder joints. It’s time consuming, but you would be surprised how a resistor that looks perfect can actually be open, and measure in Megohms. That can throw the whole board out of balance electrically, and overwork other components, causing them to fail.
 
Find someone on here who has lots of restoration experience and has access to a 2275. Pull one or both of the amp board/heat sink combos and ship it/them to that person. I am not volunteering, but you should find an expert and send it to them.
 
I suspect shorted wiring or speakers or something else in your setup. It works fine at the tech's place but fails in yours.

Tom
 
I figured out the issue with my 2275 a few weeks ago and thought I'd share. It's been a bit of a saga but with a satisfying conclusion. After blowing out the unit for the third time, I returned it to the tech to repair the output transistors. He was convinced that it was because I was powering two sets of speakers and recommended getting a second receiver and going Tape Out from the main receiver into the Aux of the auxiliary receiver. Sounded like a good idea so I found a 2220b to work on. I did some restoration on it and got my 2275 back. I used a dim-bulb tester when setting up the unit and they were both going haywire with just one set of speakers hooked up. I tried all the combinations and kept getting flares. Fortunately the DBT kept anything from blowing. I was pretty over it and laid in bed researching how much a new McIntosh would cost and how I'd have to redesign the record cabinet I build to fit it. I turned off the lights and a lightbulb went off over my head. It was the speaker wire connectors! I'd read that output transistors blew because of shorts but I didn't find any on my cables. But I didn't think of the connectors. I'm using 12AWG speaker wire and the Marantz has the spring clip terminals. The fat wire wouldn't fit so I got some Monoprice pin connectors. They worked fine for the first few months of having the setup, but more recently I was stuffing the connectors into the terminal and the metal bodies were touching creating shorts. I got out of bed at one in the morning and wrapped them all in electrical tape and it worked. I've been able to power both sets of speakers and it sounds great. So much cleaner than before the restoration. Anyway, I realize that's a dumb mistake that most people would've caught immediately but for some reason it never occurred to me, especially since it worked in the beginning for so long. Thanks for everyone who shared their feedback and tried to help me along.
 
I had the same thing happen a couple of years ago with my 2325. I had always directly connected my speaker wires to the terminals, but as you know, the hole size in those terminals is kind of limiting. So I bought some Parts Express braided end speaker wire terminals to make the setup a little neater. Didn’t play the 2325 for several months, and when I did, it was cutting in and out something terrible. I actually forgot about the new jacks until I disconnected everything to open it up. As soon as I saw them, I removed them and went direct. Problem solved. I guess the speaker protection relay saved me. Anyway, I never would have thought those external metal cases would be in contact with the wire itself, but apparently it was. I’m back to straight connection on all of my units. Nice job figuring it out. :thumbsup:
 
Being a paranoid, I put electrical tape around banana plug bodies going into speakers, and would do the same to the body of a plug going into my receivers.

Made plenty of other gaffs like a filter cap in backward, an OT not seated against a heat sink properly. Has me thinking "what could possibly go wrong" all the time in an effort to come up with a method/setup/technique to counteract the scenarios I can imagine.
 
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