The 20 Minute Marantz

[bubau]

Recently purchased a Marantz 2035b. I love this amp! Totally happy with the sound and build, but after about 20 min. of use the amp consistently cuts out. Sounds like speaker protection relay kicking in. Only way to get the sound back is to power amp off and on again, but sound will cut out again after about 30 sec. When I let amp cool off it is good to go for about another 20 min before it happens again. Had a tech look at it. He re-soldered some capacators around power supply. He put some speaker loads on it and ran it for over an hour... no problem. I bring it home and I have the same problem again with my speakers. I have tried 3 different sets a speakers individually (all 8 ohm) and same problem. Just tried a small set of computer type speakers and ran the amp at low volume. Amp ran for almost 2 hours this time but then finally cut out again. I have read about speaker protection issues but it didn't exactly sound like my scenario. Anyone have any thoughts?

[EchoWars]

New tech?

I'd try that for starters.

[skibjr]

New tech?

I'd try that for starters.
:lmao: :lmao: :lmao:
I wonder if that "tech" ever heard of freeze spray!

Seriously, you most likely have a thermally defective transistor, either on a driver board or in your power supply. Or, possibly a bad solder joint, but not as likely. After your unit warms up and cuts out, most techs would just start spritzing transistors with freeze spray until they find the troublemaker. Seems like it would be an easy fix for any halfway-competent tech.

[mhardy6647]

yup, "freeze-mist" is a wonderful thing for intermittents that fail after things get warm.

[TechMaster]

Well guys, I'm that "new tech" you speak of. Of course I tried the freeze-mist, nothing changed. The offset on this channel was at 2.5 volts(very bad). That should have triggered the protection circuit instantly, but it didn't. So I went to work with the schematic and finally came accross some odd voltages in the
current regulating circuit in the input stage. Unsoldered some parts to get a true reading and found that one the transistors was leaky :tears:
In this case, the transistor H704 was at fault. I replaced it and adjusted
the offset to near ZERO volts. The receiver now works like a charm. :yes:

[wank]

Nice work. Competence is a such a rare and wonderful thing.
Now - any chance you're in Indianapolis?

[bubau]

Hail to the TechMaster. I can't stump him. He fixes everything I throw at him. I'm thinking of becomming his agent. The 20 Minute Marantz is now a Marathon Marantz.

[TechMaster]

Hmmm .......... Maybe I SHOULD stay in Calgary !

[SB Marantz]

Well guys, I'm that "new tech" you speak of. Of course I tried the freeze-mist, nothing changed. The offset on this channel was at 2.5 volts(very bad). That should have triggered the protection circuit instantly, but it didn't. So I went to work with the schematic and finally came accross some odd voltages in the
current regulating circuit in the input stage. Unsoldered some parts to get a true reading and found that one the transistors was leaky :tears:
In this case, the transistor H704 was at fault. I replaced it and adjusted
the offset to near ZERO volts. The receiver now works like a charm. :yes:

Looks to me as the differential amp.

Yes, ofcourse, when one of them is broken you will get a nice dc-offset :D

[TechMaster]

Exactly right

[alexkerhead]

Great deal, I love seeing old audio equipment, repaired correctly(especially marantz).

bubau, I am glad you have a great tech now.
He made it sound so easy, and I know it wasn't.

[Paul C]

My TX-860 would do this, run a while and quit, but then it would come back on and run a while. I found the area by wiggling parts on the board. Turned out to be a bad solder joint one one of the caps in the power supply. Touched the iron to it and the solder ran away from the lead. I got all the old solder off, scraped the lead with an Xacto knife, and resoldered. Been running fine since.

I'll bet that is why I was able to pick up this receiver so cheaply.

[stuwee]

Well guys, I'm that "new tech" you speak of. Of course I tried the freeze-mist, nothing changed. The offset on this channel was at 2.5 volts(very bad). That should have triggered the protection circuit instantly, but it didn't. So I went to work with the schematic and finally came accross some odd voltages in the
current regulating circuit in the input stage. Unsoldered some parts to get a true reading and found that one the transistors was leaky :tears:
In this case, the transistor H704 was at fault. I replaced it and adjusted
the offset to near ZERO volts. The receiver now works like a charm. :yes:

I hope you enjoy this site! Allways nice to have another Tech in case some one gets stuck on somethingand someone else has been there before to offer info!