Smoked 2330 - Both Channels Crispy

[EastPoint]

Hi folks. I picked up a Marantz 2330 a while back, untested. It smoked from both channels so I put it away for a while. I paid Noah Schumacher to restore it but he never did. I dug it out and opened it up yesterday. It has clearly had someone in it--one of the power supply heat-sinked transistors was replaced with an NTE.

Both amp boards are FRIED. I mean, we're talking 10-12 resistors per board, ranging from dark brown to actually burned up. Wow!

So I have the service manual from hifiengine, and I can puzzle out the resistor IDs. The manual claims most of the resistors are 1/4W. Is that true? Is there any harm in replacing them with 1/2W? Also, the manual says each board has a 1k and a 2k trimmer. Any suggestions on which ones to use?

I plan to replace all the capacitors and transistors on each board with modern equivalents, as well as all the outputs and the trimmers.

I did try it with both amp boards unplugged and it comes out of protection just fine and lights up.

 

[OFrank]

Yes, you can use 1/2 watt in place of the 1/4 watt resistors. Just beware that they are a little larger and space may, in some cases be an issue. Also consider beefing up the power resistors on the board. Again beware of the size.
'O'

 

[quaddriver]

hold on, I have not looked at the 2330 SCM in a few years but a lot of times, the high stress, low wattage resistors in the amp are safety valves - designed to pop. are any listed as flame proofs? if so, that is because they are expected to explode.

 

[EastPoint]

They had better not be flame-proof. They sure flamed up pretty well.

 

[Jailtime]

Must be time to rescue butchered 2330s, I have one that somebody hacked up too.

I have Bourns PN 3362W-1-102LF and 3362W-1-202LF for the trimmers. I've used them in a 2275 and 2285. Leg spacing on them is on the small side, but they do work.

 

[EastPoint]

Perfect, thank you! I'll get those ordered as well as any resistors needed, and keep this thread updated.

 

[wlhd1610]

I just did a full restoration on one last fall and have another here to do this winter
Let me know if you need some pics or board component layouts.

Bob

 

[EastPoint]

Thanks Bob. Between the two boards I was able to read the resistor numbers and I have replaced what I can and will order what I don’t have.

I do have a question, though. Both amp boards are smoked thoroughly with 10 to 12 burnt resistors on each one. However, the outputs seem to test good. Is that possible?

 

[dave404]

EastPoint
Explain what you mean by "the outputs seem to test good". Did you actually put a signal through them? Or did you just check voltages? When you power it up, do the replaced resistors feel warm, or hot? If the resistors fried, they got WAY too much current or voltage for them to handle.

A derivation of Ohm's law says Power = Icurrent * Evoltage (where Icurrent = Evoltage/Rresistance). Resistors are sized based on how much power they can effectively handle. Say the voltage drops 16v across a 1k resistor. Then at .25watts the max current for a 1k resistor would be 16mA. (.25 = .16 * 16) This is a small current which would point to the "upstream" portion of the amp, prior to the power output transistors.

Something shorted, more than likely an active silicon based component, or a capacitor got punch through, tho not as likely. I would treat all transistors and diodes in the upstream portion of the amplifier as suspect even if it "seems to test good".

Did you take pictures of the board with the burnt resistors? BTW, you didn't say what you ended up using but I would replace with like components; if there were .25 watts resistors used in the original, that's what I would put back in. Composite type could change from carbon to film tho.

Keep us updated.
Cheers

 

[EastPoint]

I tested a few of the outputs and they didn't test shorted. That's all I have. I haven't powered up the amp boards yet, I still have a bunch of resistors in the mail. I am planning to shotgun the entire board--transistors, capacitors, and all the damaged resistors, before I power it up again.

 

[Mike Sweeney]

Dont shot gun. If something goes wrong, you will have no idea exactly where the issue is. Pull the amps out and tape off the cable ends. Since you plan on a complete rebuild.. pull and replace main filter caps straight away. Then the Power supply board. That's going to give you a solid base to work from for everything else. I also give the controls a quick shot of DeOxit at this point. Not a final cleaning. My next is to pull and replace or R&R the power switch and add/replace the snubber. Right there is many issues resolved on older units. IN your case, probably not so much but you can now start to R&R the amps. Get a cheap transistor checker for 20 bucks or a cheap meter that can do it. You can do it the harder way with the diode setting on a meter but I like the new cheap checkers for fast checks, ID of what type and an HFE number. Plan on new transistors.. I dont mess around anymore with the old ones.. too often they have been abused and not up to the challenge. New transistors are pretty cheap compared to the time it takes to take it all apart ( again) to replace them if they end up bad or weak or dying with all the shiny new parts in place. I've also taken up the habit of replacing the carbon composition resistors with new carbon films. I stay like for like.. 1/4 to 1/4 watt, 1/2 to 1/2 etc. The bourns are an excellent choice. I'm skimming ALOT here but i think you get a general idea. The electrolytic cap below 3.3uf get replaced by film caps. There is some discussion about the special low ESR electrolytic that are in some locations vs films but I cannot hear a difference. I've also taken to replacing the shielded connecting wires on the amp boards to the RCA jacks. The shielded cord that guitar makers use in electric guitars is almost a perfect match. I replace it because it tends to be old/stiff and somewhat brittle and tricky to solder without melting the hell out of the core. Whew.. there are a ton of posts with exact BOMs or near exact lists with plenty of opinions on the finer points

 

[dave404]

Dont shot gun. If something goes wrong, you will have no idea exactly where the issue is. Pull the amps out and tape off the cable ends. Since you plan on a complete rebuild.. pull and replace main filter caps straight away. Then the Power supply board. That's going to give you a solid base to work from for everything else. I also give the controls a quick shot of DeOxit at this point. Not a final cleaning. My next is to pull and replace or R&R the power switch and add/replace the snubber. Right there is many issues resolved on older units. IN your case, probably not so much but you can now start to R&R the amps. Get a cheap transistor checker for 20 bucks or a cheap meter that can do it. You can do it the harder way with the diode setting on a meter but I like the new cheap checkers for fast checks, ID of what type and an HFE number. Plan on new transistors.. I dont mess around anymore with the old ones.. too often they have been abused and not up to the challenge. New transistors are pretty cheap compared to the time it takes to take it all apart ( again) to replace them if they end up bad or weak or dying with all the shiny new parts in place. I've also taken up the habit of replacing the carbon composition resistors with new carbon films. I stay like for like.. 1/4 to 1/4 watt, 1/2 to 1/2 etc. The bourns are an excellent choice. I'm skimming ALOT here but i think you get a general idea. The electrolytic cap below 3.3uf get replaced by film caps. There is some discussion about the special low ESR electrolytic that are in some locations vs films but I cannot hear a difference. I've also taken to replacing the shielded connecting wires on the amp boards to the RCA jacks. The shielded cord that guitar makers use in electric guitars is almost a perfect match. I replace it because it tends to be old/stiff and somewhat brittle and tricky to solder without melting the hell out of the core. Whew.. there are a ton of posts with exact BOMs or near exact lists with plenty of opinions on the finer points

What Mike said.. too many people shotgun these things and end up making it worse than they should

 

[EastPoint]

OK, so this is kind of hilarious. I redid both amp boards with new resistors in place of the burned ones, new trimmers, new electrolytic caps, and new small transistors. The driver transistors and outputs all test fine. I also completely rebuilt the power supply--new transistors, including the two heat-sinked 2SD331s, new capacitors, and new double diodes.

I powered it up on a dim-bulb, one amp board at a time. It works fine. Seriously. I don't know what fried the hell out of the boards, but it wasn't blown outputs, that's for sure. Seems to play fine, though it is NOT happy on the dim-bulb. I'm going to take it off the bulb and set the voltages, then probably rebuild the rest of it. Completely bizarre. I wonder what happened to it.

 

[Steven Tate]

I wonder what happened to it.

Maybe someone shorted some speaker terminals or had a speaker go short at some point?

 

[wlhd1610]

On the bigger amps/receivers I start with a 100w dbt and if ok move up to a 300w just for peace of mind before I hit it with full line voltage.
I also have it plugged into a Kila-Watt to monitor current draw just cause I can!

Bob

 

[EastPoint]

So it's running now but it has occasional fairly loud crackling on both channels, independent of volume. I plugged into the main ins and the noise went away, so presumably it's on the preamp board that I haven't done yet.

I'm also getting pretty aggressive drop-outs on both channels that go away when I crank the volume. I am guessing it's the source selector, which I already Deoxited but is still causing trouble. I replaced the relay but no change.

 

[EastPoint]

Redid the preamp board and everything seems fine now. No more crackle after I redid the four transistors, and the dropouts have gone away too. Just waiting for the main caps from Digi-Key, since Mouser is out of stock, and we should be good.