Proton D940 - worth saving?

Uncle Bambi

Uncle Bambi

Funky Tut
I saw this one at the local swap meet on Saturday. I have never heard of Proton but the unit was heavy and appeared well built, and at the price he was asking I figured I'd take a chance (also, it looked like a better version of my NAD 701). If anyone has some in-depth knowledge of this brand/model, I'd love to be persuaded to save it.

I brought it home and did a bit of research..... not too much info to be found. I plugged it into my DBT, and fired it up. No right channel, but the left sounded good and the tuner worked great. So, I pulled the cover (which is what I should have done first, and was mildly astonished.

The first thing I noticed was that there was a power supply capacitor missing:

Proton D940 2.jpg

Then, I found out that it wasn't really missing, after all:

Proton D940 1.jpg

Turns out, it had "bulged" itself right off the PCB:

Proton D940 4.jpg

Also - it appears that they bought their glue from the same vendor as Sansui:

Proton D940 3.jpg

This has got me wondering if this thing is worth saving. I've no real use for it, and I do have other projects waiting on the stack. I haven't grabbed the schematics off of HiFi Engine yet, but looking at the layout I'm guessing that popped cap is the reason that the right channel is out. The capacitor arrangement is mirrored on the other side of the PCB, suggesting two identical signal paths. Might be an easy "fix" to get it running..... but then I'll need to address the glue, and that one popped cap calls all the rest into question so I'd probably be remiss if I didn't do a complete re-cap on the unit.

Ugh.
 
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Uncle Bambi said:
Proton D940 - worth saving?
Click to expand...

Generally yes it sure is. Although a big determining factor for me is the outside cosmetic condition. The electronics can be addressed if it doesn't work right, but looks like there's plenty of work to be done inside of that one.Someone else has obviously be inside messing with it for the heat sink fins to be bent like that.

958260-amazing-proton-d940-receiver.jpg
 
glen65 said:
Generally yes it sure is. Although a big determining factor for me is the outside cosmetic condition. The electronics can be addressed if it doesn't work right, but looks like there's plenty of work to be done inside of that one.Someone else has obviously be inside messing with it for the heat sink fins to be bent like that.
Click to expand...

Thanks for the reply. Yeah - I noticed the bent heat sink fins after making my initial post. The cosmetics are OK, not stellar..... maybe a 7/8 out of 10. Mostly because of the cover though, the face plate looks pretty good. Lots of cat hair throughout, as well. Yuck. I'll drop in a new cap where the missing one should be, see if I get the right channel back, and go from there. The corresponding cap on the other side looks to be bulging off of the PCB as well, so that'll need to go as well. Those caps are 470uf 100v

Specific to this unit question - do you (or anyone else, for that matter) know of tips or tricks to get the top PCB out (the one with the tuner on it) so that I can get to the underside and replace the corroded components? It looks pretty wire-bound and inaccessible to me.

General question - C308 has corroded, broken leads and needs to be replaced. It is a .022uf 50v Mylar capacitor. OK to replace with a electrolytic of the same value?

Random rhetorical question.... why is it that I have literally hundreds of fresh, new replacement electrolytic capacitors on-hand, but I never seem to have the value I need?
 
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NAD was related to Proton at some point (sharing some design and manufacturing resources), so this is actually a pretty good unit. A couple of notable features. First, this has the Schotz FM tuner, which was great at pulling in more distant stations cleanly. (I forget how it worked, but Hans Fantel wrote about it in the early 80s here.) HiFi Engine has a copy of the owner guide and service manual here.

Another feature--the power amp section has about 6dB of headroom. This receiver is rated at 40 watts, but during instantaneous peaks (up to 200ms), it can deliver up to about 150-160 watts.

I had a pair of their car amps back in the early 80s--they were some of the nicest sounding amps I owned. They, too, had large headroom ratings, and the larger amp had the soft clipping feature to protect tweeters.
 
Uncle Bambi said:
Specific to this unit question - do you (or anyone else, for that matter) know of tips or tricks to get the top PCB out (the one with the tuner on it) so that I can get to the underside and replace the corroded components? It looks pretty wire-bound and inaccessible to me.
Click to expand...

There's really no easy way I'm aware of to pull the board. If you do it just take plenty of pictures so that you can see where the wires were placed before you start.

General question - C308 has corroded, broken leads and needs to be replaced. It is a .22uf 50v Mylar capacitor. OK to replace with a electrolytic of the same value?
Click to expand...
Don't replace a mylar with an electrolytic.

Random rhetorical question.... why is it that I have literally hundreds of fresh, new replacement electrolytic capacitors on-hand, but I never seem to have the value I need?
Click to expand...

One reason is simply because there are many more available and used. Physical size can also be an issue. Sometimes even if you have the right value and voltage it won't work, because of physical size constraints in the area the cap is being placed.
 
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I still have the 940 I bought new although it's in semi-retirement now, occasionally serving as a stand-by unit when something else is out for servicing.

A great little unit packed with useful features. Biggest issue is the input selector switch which often needs to be played around with to get both channels to play. So that could well be the problem right off the bat. Apparently the selector switch is sealed making it almost impossible to get cleaner products inside. Same issue applies to the REC output selector switch as well.
 
As others have stated, nice unit that offered very good bang for the buck when I was selling them and the somehow related NADs over 25 years ago. They do share the same issues as NAD, build by low bidding contract manufacturers using cheap parts to keep the price down and give that good sound for the $. They are prone to issues but if found cheap worth a shot at savings. That one has a dual rail power supply like the NAD Power Envelope IIRC and had great dynamics and yes, a great tuner section.
 
glen65 said:
The WIMA caps would be fine, but the leads aren't very long. So make sure the lead spacing on the board will allow them to simply set in place before soldering.
Click to expand...

Oooooh! Thanks for that - good catch! The ones I linked to were 2.5mm lead spacing, and I need 5mm lead spacing. You saved me a fair bit of frustration there!
 
glen65 said:
No, Isn't the original .22?
Click to expand...

That's what I typed in my earlier post. When I checked the SM, it specified ".022uf +/- 5%". So I went back and looked at the component..... tuns out the marking was so faint that I misread it, and it is indeed marked .022J, which translates to .022uf 5%.

I'll go edit my previous post..... but I am very grateful that you are noticing my errors and helping me along.
 
Uncle Bambi said:
That's what I typed in my earlier post. When I checked the SM, it specified ".022uf +/- 5%". So I went back and looked at the component..... tuns out the marking was so faint that I misread it, and it is indeed marked .022J, which translates to .022uf 5%.

I'll go edit my previous post..... but I am very grateful that you are noticing my errors and helping me along.
Click to expand...

The cap would function in circuit OK. But it's not made for mounting the way it needs to be because of the type of cap it is.
 
glen65 said:
The cap would function in circuit OK. But it's not made for mounting the way it needs to be because of the type of cap it is.
Click to expand...

Yeah - I was thinking of mounting it upright, with some shrink tubing on the exposed lead. Since I have the WIMA on the way from Mouser, I think I'll set it aside for now.. I'll just wait for the order to arrive, as taking this thing apart is something I only wish to experience once. :)
 
I have a Proton 940 that I enjoy very much. Very similar to an NAD 7240, but with some upgrades. Has the record out function, has an aluminum face plate (instead of plastic), and has mm/mc choice for phono as well as capacitance. The only thing I don't like about it is the small volume knob and lack of a -20 db button (like the NAD has. This makes it a little hard to control volume at lower settings. If not for that I would take it all day long over my 7240. I had no problem following the video and cleaning out the input selector as mine was scratchy at first and would occasionally drop a channel.

I would say this is definitely worth saving. When Crutchfield had them, they claimed it was the best sounding receiver they sold.
 
Drum said:
.......I had no problem following the video and cleaning out the input selector as mine was scratchy at first and would occasionally drop a channel.
Click to expand...

Turns out it was very easy to disassemble for servicing. I replaced the two caps in the power supply (one that was missing, and the other that was bulging), the corroded/broken film cap, two corroded but still functional resistors, and a corroded jumper. Put it back together and both channels are now active and strong.

Boy, does this thing have a good tuner section. I think I'm going to keep this one and sell the NAD.
 
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Nice! Sounds like she's a keeper. The Schotz tuner is a nice bonus on top of everything else.

I remember Proton sold standalone tuners as well. It makes me think of picking one up just for kicks.
 
Wildcat said:
Nice! Sounds like she's a keeper. The Schotz tuner is a nice bonus on top of everything else.
Click to expand...

Yeah..... the thing is, I'm not thrilled about the cheap electrolytics throughout, and I really don`t feel like doing a total recap. I'm on the fence with this one.
 
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