Lost bias on Marantz 1060 right channel

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Hi all,

I was fixing a Marantz 1060 for someone. Turned out to be a poor contact in the Mono switches. A bit of DeoxIT solved the problem.

I decided to adjust the bias as I found the unit sounded a bit strange. Found the service manual, and lowered the voltage across R747, R748 from 11mV to 7.5mV.

I let the amp running a while, and then, a little pop came from the right channel. Turns out one of my alligator probes moved a bit and shorted two contacts together. I don't know which ones though, as I removed the leads as soon as I found out...

Now, the right channel has 0mV bias... There's just distorted sound coming out. I used an RCA cable between the pre out and main in to be sure the preamp is OK, no problem there.

I checked the voltages and resistance around the bias pots and compared between the two channels. The varistor and diode around the bias pot seem to be OK, I read the same dropout, etc.

In the measurements I've done, I found:
- The right channel's overall voltage is a few volts lower than the left channel.
- 0mV at R747.
- 20V at the negative side of the right channel 3000µF cap.
- 0.01V at the negative side of the left channel 3000µF cap.
- Voltage is about the same at the positive side of the 3000µF caps. (30-something volts)

I haven't checked for shorted transistors. All I can tell is that I don't have my DMM with a sound diode checker, and my oscilloscope with me.

Any ideas? All the components in the service manual's troubleshooting area seem OK.

http://www.acec13.fr/TVC/Marantz/ressources/1060/1060_SM_MARANTZ_EN.pdf
 
Oh, one more thing, when I put the voltmeter's positive lead on the H001 collector and negative on emmiter, the resistance is much higher than doing the same reading on H004.

Should read : negative probe on base, not emitter. (The schematic and PCB are not exactly the same)

I pulled out the power amp board, pretty much every readings I've done on both channels are the same.

I might have found the problem. Diode H715 (1N60) looks a bit smokey, like a blown fuse, however reads fine on the multimeter (note that I do NOT have my multimeter with diode and hFE tester).

My local store has some 1N60 and quite a few other germanium devices, so I'm OK. I love these diodes, you can see when they fail :D

If it still doesn't work, I think I'll have a look at H005 and H713, but they seem fine. Fortunately (or maybe not) my local store has ECG replacements for the SV-3A, it's not the case for the S3016 R, for which I found a spec chart, by the way.


So far, reading this topic helped a bit understanding the circuit.
 
Hi Giaime,

I ordered extra transistors (3 driver sets and 5 output transistors) to first test the amp without checking every components, and if it breaks again, then test everything.

But, I should probably test the transistors individually. I've got a question though, can I test the transistors in-circuit? I found the dead C959 by comparing many readings between the transistor pins on both channels with the diode checker. (They all measured the same, except for the dead one)

Nothing overheated, all the diodes measure fine :bigeyes:, the bias pot still works, even all the output transistors check OK, but one makes a broken glass sound when I shake it... (The die can't be disconnected... It measures fine.)

and when you replace transistors, make sure they're not fake, as happened to me

Don't worry, I got some samples directly from ONSemi, with complementary transistors possibly coming from the same batches (they have the same internal code). :D (There are S&H fees though)

Maybe I could temporarily try with BD139/140, my local store has those. (But I don't want to put back the possibly broken output transistor in service...)

I'll start to check resistors in-circuit, if I see highly different values between both channels, I'll start looking for drifting resistors.
 
Received the transistors!

Hey! I can't attach pictures...

EDIT:
onsemi.jpg


:drool: ;)
 
OK, so I replaced the 2SC959/A606 drivers with MJE340/350 on the right channel, and the one of the 2SC897 with an MJ15003.

I don't understand those who are saying changing devices would make the amp lose it's tone... (Like on AudioKarma, but it can't be considered a valid comment, as AudioKarma remains AudioKarma.)

Question 1. The 2SC897 I replaced makes some sound when I shake it, as if the die wasn't sticking to the case, but at the same time, the measurements are fine. Should I put it back, or switch all the transistors to MJE15003?

Question 2. I lost my desoldering pump (...), so desoldering the drivers on the other channel would remain a tedious job as it was for the channel I fixed. Do I really need to switch the original drivers for the MJEs?

Question 3. There are currently no heatsinks on the MJEs, I'm not driving them too hard. Do I need to find TO-225 heatsinks? (Is there anything compatible?)
 
There are TO-126/TO-225 heatsinks, but I doubt you need them on a 30WPC amp.

Oh, there's no real difference between TO-126 and TO-225, I was starting to wonder... Fairchild sells the MJEs as TO-126, and ONSemi as TO-225.

Heatsinks are suddenly much easier to find :D (They're all made for TO-126)

I tried the amp louder, the drivers and output transistors don't touch warm at all, however there's a funny feeling when you touch the individual output transistor small heatsinks (kidding;)). It looks like the whole amp wouldn't need any cooling at all.

I'll try to find heatsinks at my local store, and if they don't have them, I'll order $0.05 ones with my next Mouser order sometime.

Now, where to find a 51mm dia., 68mm L, >=80v, >=4700µF capacitor...

BTW, are there any risks putting higher value caps for the DC-coupling electrolytics?
 
Shouldn't be any risks - larger would be better :) and I would definitely recommend replacing them as well as the main filter cap.

The originals are 3000uF 55V - 4700uF 63V should do fine, and will probably fit easily. Likewise for the main filter cap, you could probably get a 10,000uF 100V unit in there. Don't go overboard though - an amp this old won't be worth it.
 
as well as the main filter cap.
Problem :
Now, where to find a 51mm dia., 68mm L, >=80v, >=4700�F capacitor...

I've looked at Digikey and Mouser, both don't carry 2" / 50.8mm dia. capacitors, and when they do, they're $20+ screw terminal or snap-in caps. 35mm ones are cheap and very easy to find on the other side...

EDIT: Newark, AES and Allied, same thing...
There's one at NewArk for $26 though.
 
I didn't replace any caps finally.

So, I've heard back from the 1060 owner recently, and the channel apparently failed again. I haven't heard how it sounds like, so I'm not sure if it's a bias issue or anything else. The owner found a separate power amp to use instead.

Anyways, I bought a 1060 as well. It was working perfectly until yesterday : there's crackling on one channel, so I used a freeze can and spotted the first transistor (2SC945) in the power amp stage. It seems it's not just caused by the PCB solder joints, it looks like the internal joints are failing as well...

Edit: My local store has some C945 :cool:
 
Hi..
I have 1060 myself and trying to find why my left speaker is crackly and soft..

My left channel is all crackly and soft and i have checked all the way along the line on schematic..found my 3000ums have different voltage on positive - right is 32 v and the left is 9 v - yours were both 30 when you posted so i guess this could be reason..any ideas why??
 
J715 32
J716 9
J713 32
J714 9
J709 and J710 are both 80

I traced J710 to R714 which is 80v on one side and 13v on the other, R713 which is J709s equivalent is 80v on one side and 50v on the other.

This is the first place that there is a difference from what i can tell, everything after that is obviously 32v and 9v up till the big 3000 resister things.

I really have no idea - just trying to use logic...

What do you think?

Thanks heaps for your reply...

Dave
 
Wow!!.....this is a delightful post....but I'm such a rookie that I barely understand it all! I too have a 1060 with a dead channel.....and I'm going to replace the output transistors just to see if that fixes the amp. Any suggestions would be appreciated.....I believe it has all original OTs in it now.....the 2SC897s. In changing the two.....I figured I change all 4. The mentioned MJ15003.....is that readily available, and are there any other changes I should make in order for these replacement OTs to function properly? Thanks, Tom D.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.