2240 Help.

Derek G

Active Member
Hello,

I've been enjoying a 1974 2240 for over a year now. It was handed down from a close friend. The condition of this unit was pristine inside and out. I few months back I replaced all the fuse lights with leds. Turned out amazing. The only thing that I could not seem to figure out was the stereo light not coming on during "good" fm reception. Everything else was silky smooth. After doing a little research, I found this to be not uncommon. Wasn't a big deal anyways. Just the other night I was listening to some lps and out of nowhere I lost audio going to phono? I immediately starting to investigate when I lost power to the unit completely. Shortly there afterwards I smelt the dreaded scent of electrical doom. Dammit!!! Anyways, after opening her up I've narrowed the stench down to the the power board. P800. Nothing stands out as being fried, but I'm sure its coming from this power board. I don't understand what caused the whole unit to power down though? The main fuse on the back of the unit checks out. I expected to find more internal fuses possibly on the power board, but nope? Could a bad cap or resistor on P800 cause this without blowing the main fuse? I ordered and received all new caps for P800. Im no pro. Im would like to say this is an easy fix without sending this unit to a repair shop. Im 300 miles away from someone that would look at it. I downloaded the service manual. Any tips would be grateful. Ty so much in advance.
 
Welcome to AK, bummer on the 2240.

While the marantz gurus are asleep maybe I can get you started.

Normally smoke is due to a burning resistor typically in the
power supply or power amp stage. Need to identify the failed
component and then work out why it failed and fix the root cause.

If you are comfortable working on a live amp (lethal voltages inside)
then will get you to do a basic health check. If you are uncomfortable
with this (not worth dying for) then that's ok, maybe there's an AK
tech in the area.

Measure dc voltages at the following points on the P800 board, connect
black multimeter probe to chassis, phono ground or any black speaker post
- J804 (35Vdc)
- J806 (14Vdc)
- J809 (<100mV), right power amp
- J810 (<100mV), left power amp

Please don't power on the amp again until asked by an Aker. Try and
find that burnt resistor(?)

upload_2018-10-30_19-35-29.png
 
Thank you so much for the quick reply. I will measure voltage and report back asap.




Welcome to AK, bummer on the 2240.




While the marantz gurus are asleep maybe I can get you started.

Normally smoke is due to a burning resistor typically in the
power supply or power amp stage. Need to identify the failed
component and then work out why it failed and fix the root cause.

If you are comfortable working on a live amp (lethal voltages inside)
then will get you to do a basic health check. If you are uncomfortable
with this (not worth dying for) then that's ok, maybe there's an AK
tech in the area.

Measure dc voltages at the following points on the P800 board, connect
black multimeter probe to chassis, phono ground or any black speaker post
- J804 (35Vdc)
- J806 (14Vdc)
- J809 (<100mV), right power amp
- J810 (<100mV), left power amp

Please don't power on the amp again until asked by an Aker. Try and
find that burnt resistor(?)

View attachment 1318284
 
I have no voltage to the power board. No voltage to the main filter caps. No voltage to front panel. AC outlets work. Switched and Un switched so its not the power button. I've browsed through some treads on here and I suspect I may have a bad transformer. Ive read some have fuses, but they are next to impossible to replace. I found a used one for $50. Removing it looks to be a nightmare unless I just label and cut wires. Which is what it looks like they did with the used unit. Re solder and heat shrink? Anyways, can someone inform me as to the best way to check resistance on this transformer? To rule out any other possibility before I purchase a used one. Also, I heard its rare they go out so... Any further help would be very much appreciated. Thank you in advance....:)
 
EDIT: Corrected.

With amp powered off unplugged, check the transformer primary by measuring resistance
between the blue and white wires as per below

upload_2018-10-31_9-37-28.png.
 
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schematic shows transformer internal fuse .. it is however too late if the transformer smoked ..
unplug the unit from the wall then measure ohms between the blue and red wires coming from the transformer .. this will say if the transformer primary is open circuit or not .

EDIT well thats if usa model according to this schematic
 
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After further review, de soldering the transformer wiring harness from the original pin locations shouldn't be to difficult. Taking some pictures for ref and labeling everything.
EDIT: Corrected.

With amp powered off unplugged, check the transformer primary by measuring resistance
between the blue and white wires as per below

View attachment 1318789.
Do I need to remove and open the transformer do perform this? I see the blue wire runs directly to the main fuse. The white wire runs to the a/b bridge underneath the main filter caps. I get zero resistance checking from the outside?
 
Gremlins at work, info in post #5 is incorrect. Check transformer primary by m,easuring resistance between red and blue wire.
Apologies.
 
Oh ok. Zero. Nothing. Nada....:(
I removed the transformer and labeled everything. I wanted to open it up and check the fuse, but I don't see anything in here. It must be buried really well. Can I assume this guy is toast? Any further testing? Blue and red wires show zero ohms either way.... This transformer looks perfect. No damage noticeable. No smell. But unless I testing it wrong
 
Can anybody else chime in? I ordered another transformer that just happened to be on eBay for $50. I'm assuming this thing is smoked but I read that the main unit fuse would have gone first and it looks and tests good. Also, what would have caused this to fail? I read its rare they go bad. My skills are very limited testing and chasing these circuit boards. Im learning quick though. I have all new caps for P800. I'm reading about replacing a few transistors on it as well. I have new smoothing main caps to. All the other boards appear to be fine. Even on P800 everything appears ok, but when the unit powered off the electrical fire smell was coming directly from it so Im assuming something cooked. Anyways. Anything else I should check for before firing up the used transformer when it arrives. Thank to all who reply. Oh, and Happy Halloween.....:)
 
Folks are correct, transformers rarely go bad without something else dragging them down. With that said, I have seen on occasion, the windings short out but it's rare. You would see zero ohms or an "off" reading depending on where the short is in the winding. If you should see say, 600 ohms but only see 200, thats a short. An "open" is not zero ohms, its infinity on the reading. That would be a busted winding. Either means the transformer is toast unless it's really rare because you can get them rewound if you know the build details.

And you are sure it's not the power switch? they tend to cook themselves over the years. I've seen them show they "work" but are so carboned/burnt up they cannot pass enough current for anything to work. This one just came out of my current 2245.

IMG_6853.jpg IMG_6854.jpg
 
Folks are correct, transformers rarely go bad without something else dragging them down. With that said, I have seen on occasion, the windings short out but it's rare. You would see zero ohms or an "off" reading depending on where the short is in the winding. If you should see say, 600 ohms but only see 200, thats a short. An "open" is not zero ohms, its infinity on the reading. That would be a busted winding. Either means the transformer is toast unless it's really rare because you can get them rewound if you know the build details.

And you are sure it's not the power switch? they tend to cook themselves over the years. I've seen them show they "work" but are so carboned/burnt up they cannot pass enough current for anything to work. This one just came out of my current 2245.

View attachment 1320049 View attachment 1320050
Thanks for the reply. The power switch works for the "switched" acc plug in the back, so I ruled it out? Haven't opened it up. So your saying with my transformer being "open" as in zero reading its 100% damaged correct? I'm just wanting to be sure I'm testing this correctly to be faulty.
 
Some power switches have two sections or 'poles', one for the unit and a separate one for the switched outlet.
Most meters read zero for zero Ohms and OL for an open. Power transformers have very little DC resistance.

Tom
 
Some power switches have two sections or 'poles', one for the unit and a separate one for the switched outlet.
Most meters read zero for zero Ohms and OL for an open. Power transformers have very little DC resistance.

Tom
Tom, ty for your time. I already heard great things about your expertise on these receivers reading through other posts. Anyways, I just pulled the power switch out. It appears it has only a single output being used. Does this confirm the switch working via "switched" outlet on the acc. Anything else you can think of to check browsing this post? Now that I have the transformer removed my options are powerless, but from everything Ive researched and tested I was told its "dead". I was really hoping to be able to test this transformer and rule it out as the 100% culprit. I've had conflicting reply's regarding checking resistance. I snagged a used unit off the bay yesterday. Im just hoping I didn't miss something because this one looks perfect. Anything thing else you can advise me to check prior to installing the "new/used" transformer? Should I replace this power switch seems I have it out?
 
Tom, ty for your time. I already heard great things about your expertise on these receivers reading through other posts. Anyways, I just pulled the power switch out. It appears it has only a single output being used. Does this confirm the switch working via "switched" outlet on the acc. Anything else you can think of to check browsing this post? Now that I have the transformer removed my options are powerless, but from everything Ive researched and tested I was told its "dead". I was really hoping to be able to test this transformer and rule it out as the 100% culprit. I've had conflicting reply's regarding checking resistance. I snagged a used unit off the bay yesterday. Im just hoping I didn't miss something because this one looks perfect. Anything thing else you can advise me to check prior to installing the "new/used" transformer? Should I replace this power switch seems I have it out?
 

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I just finished up recapping the power board p800. I replaced all 8 electro caps. 1 ceramic. 1 film. I replaced the 5w 150 ohm 10% through hole resistor at r807. I could only find a replacement at 5%. Told that shouldn't matter. The resistor looked rough and the metal leads were green. I know this part gets hot. I also discovered a bloated rectifier at h808. See pic. I replaced both h808 and h811. Not sure if this damaged rectifier could cause this unit to shut down. Doubtful. I'm still stumped as to why there isn't an internal fuse that shut this 2240 down completely. Thats why Im leaning on a dead transformer......But. Im a rookie. I'm leaning things though and Im having fun. Im discovering I really enjoy this and want to advance my knowledge of this trade. I just hope this all ends will my beloved 2240 back in the heart of my living room. My buddy gave me a loner hitachi sr-903 to fill the void in the meantime. She's not to shabby. Anyways, thanks to everybody who contributes to bringing this girl back from the dead...:)
 

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Before and After on the p800. Was thinking of replacing the relay as well? But...:idea:
 

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back to the transformer testing .
set your meter on 200 ohms and touch the probes together and note the reading . separate the probes and note the reading . now touch those blue and red wires again and note the reading .
 
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