Repair Help Needed on Marantz 250 Power Amp


Hello, I am a newbie to this site. Tim Tengberg, the owner of HiFi Haven in Whittier, CA suggested I inquire on this site for someone to repair my Marantz 250…so here I am. 

I bought this amp six years ago. It was working. I took it to a tech in San Diego. He replaced the left channel output transistors with sets of Toshiba. The unit was working but soon something else started to fail. I took it to George Meyer AV in Los Angeles. They did more extensive repairs by replacing additional capacitors. But it wasn’t totally “recapped.” 

Last year I found a guy in New Jersey who had recapped a Marantz 3200 preamp and a Marantz 140 power amp. Since I had both, I sent mine to him and he gave them a thorough service. They came back sounding better than they did in 1974!

 

So I decided to send my Marantz 250 to him for a total recap service. He replaced the main filter caps with 22000uf Nichicon NT. He recapped the amp board by removing the cheap no brand caps George Meyer had put in. He rebuilt the meter board. Basically, he did a nearly complete recap…but he left the Toshiba and original Motorola output transistors because they seemed to be fine to him. i felt it was a mistake…but he said that setting BIAS might be more difficult if he replaced them. 

I got the amplifier back and it was working fine for about 10 hours of play time. Then one night i turned it off…and the next day it wouldn’t work — the protection relay would not kick-in. 

At first he thought it was the m=new, modified relay he put in…so he send me a new one. Since he installed a socket, it was plug and play. I plugged in the new relay. Didn’t work. That wasn’t the problem.

Next he thought it might be the bridge rectifier. But I tested and that wasn’t it. 

So we removed the right channel (original Motorola) output transistors. But then relay didn’t kick-in. I then removed the left channel (Toshiba) output transitions — and the relay kicked-in! 

I tested the output transistors, and the top two (PPN, I think) were bad. 

So…the long and short of this story is the output transistors in the left channel have gone out again. I could buy matched sets of Onsemi replacements — but those would likely just fail in time unless I can discover what in the left channel board is Actually causing the problem with the output transistors going out. Maybe its some transistors or a diode. I didn’t know. And I don’t have the skill and knowledge or equipment to figure it out. 

 

I didn’t send it back to the tech in New Jersey because he doesn’t have time to do it now and its yet another $250 roundtrip shipping expense. I was hoping to find someone qualified and experienced closer to me — possibly in Southern California.

So if anyone has a recommendation or referral — I would greatly appreciate it. 

And yes, I could sell it for peanuts, or forget about it…but it seems its just one service away from greatness! Help me save this relic of an earlier age in audio! 

 

Thank you for reading and responding. 

 

So…I am hoping to find someone 

stoddrob

Doing a quick search on /redit and other places there are lots of comments about "vintage audio" repair folks down in SoCal, LA, other areas.  

Bring it to a tech who will replace parts, then leave it at the shop turning it on/off every day for 2-3 weeks before returning it to you.  Fix one part, and the other linking part fails next in the chain etc. Or, the root cause was never found, and now you'll just end up replacing hard to find output resistors.  Good techs down there might be more expensive, but worth it if you want to get it fixed right. If they dont leave it and test on/off for at least a week after repairs you are just wasting your time, money shipping and restarting all over again each time. I'd find a Marantz specialist.  Steve @FlyHiFi vintage up here in NorCal Auburn Blvd deals with a ton of Marantz, maybe he will share more about his tech or trade-in/swap as a fix.  

buy a car you love to drive!!!!!!!!!!!!!!!!!!!!!!! you will be happy for it to break once again.

helping you step outside and glance back at yourself: work hard to find someone local, or forget it.

@stoddrob ,

You just asked the question day before yesterday. Give some of the guys in the know a chance to find your thread and respond with help like @tomic601 before passing judgement on the 'snobbery' around here.

2 small of a sample size to make that assumption about the whole site. Steve in Santa Monica is brilliant. PM me. his backlog is out into May.

Jim

I can tell this website is not what I was looking for…AudioKarma is a much better site for seeking and getting help. I didn’t ask anyone to opine on whether I should keep the amp and have it repaired or sell it or junk it. Snobbery. 

@stoddrob ,

I believe @elliottbnewcombjr  is stating he is of the opinion that this particular amplifier has become more of a problem than it is worth and it might behoove you to move on from your nostalgic attachment for said amplifier as it will most likely continue to cause you grief in the future whether you resolve its current problem or not, considering the continuing cost of resolution, and it is time to ruminate on acquiring a superior replacement. Either that, or he didn't have anything better to do today...

Was this intended to be helpful? Or did you just not have anything better to do today? Your comments are not in the least helpful, sorry to say. 

 

"Help me save this relic of an earlier age in audio! ... discover what in the left channel board is Actually causing the problem"

this unit's mystery has defied solution by highly skilled people starting with OEM parts quality control; Marantz; west coast; east coast;

I suspect you would advise a friend to sell it and live his life with something both remarkable and reliable.

Shipping Cost:

IF you fix it, You/I can easily predict future repairs, so find someone within a few hours drive so you can drop it off/pick it up.