Advice on vintage Denon PMA-730

[magreen]

Yes, there are a really good 10,000uF/63V which is 30mm and 10mm lead spacing...

http://nl.mouser.com/Search/m_ProductDetail.aspx?Nichicon/LKS1J103MESB/&qs=sGAEpiMZZMtZ1n0r9vR22f0%2bFPQ%2b4S8DEdb3sVJ4ql0=

Fabulous! Thank you. Looks like I should just be able to bend one of the leads at about 90 degrees+90 degrees to get it to fit the 14.5mm holes, right?

Edit: Hmmm... those leads have an interesting shape. (Picture here: https://www.digikey.com/product-detail/en/nichicon/LKS1J103MESB/493-13365-ND/1964508) Not sure I could bend them. What do you think?

 

[Karl vd Berg]

On some of my vintage units, I worked a bit on the PCBs and made holes (10mm spacing) to accommodate the new caps. Will post pics later... It's not a difficult job, you only need a bit of patience...

 

[lico]

Am intrigued with this thread. I kind of doubt the big 'lytcics are the real reason, but hopefully after replacement all is well.

To me it sounds more like something in the input stage to the amp. But who knows. Recently resurrected a Denon PMA-777 with new output transistors, the old Denons are good stuff.

Good luck!

 

[magreen]

@Karl: Great. Would be very interested in those pictures and any guidance you can provide (such as how to make the electrical connection after you make the hole). Thanks!

Thanks lico! One other observation I didn't mention. Using the headphone output, the frequency response appears level and I don't have the drop offs at 220hz and 130hz. That suggests to me that the input and preamp sections are fine, and the power amp section is the issue. Am I drawing the right conclusion?

 

[lico]

Would agree the power amp caps could be the issue I suppose. Then again, took a look at service manual, headphone output taps off the power amp output to speaks , which says power amp is fine with low level input if it sounds good.

Under higher load though, you could be right. I am just an amateur at fixing this kind of stuff, so wish you well. Sometimes the most obvious solutions are not obvious. Hope you get it working without having to drill holes in the PCB to make things fit.

 

[Karl vd Berg]

Agree with Ilco, and that's why I start with small caps first, specially in the power amp part with most of 80's stuff. But the PMA-730 is now a 35 years unit, and because you are there, might also worth replace the big caps, too, rather than open the unit again later to do so.

I have the feeling that the PMA-730 is a better unit then the PMA-737 I had a while ago, which is a really nice amp.

Will post a picture later of big caps in a vintage amp.

 

[magreen]

Wow, thanks to both of you, and thanks for looking at the circuit diagram for me! Ok I'm definitely going to do the smaller caps first. I might order them together with the big caps (if all from one place), but I'll start with the small ones and see if that does the trick--especially seeing that I'm new at this and the big ones require modding the board.

Do you think one more cleaning with deoxit would make a difference? I already did all the pots and all the switches, plus the rca inputs and the headphone jack.

I'm also putting together a DBT so I don't blow anything up. 60W bulb should be fine right?

 

[Binkman]

Pics? I think I see at least 4 or more potential 'cold' solder joints. If you see a 'hole' at a joint to the component lead at the lead, look with a good magnifier'. also saw couple of possible touching joints.,...that only from magnifying your poor image resolution. I'd do a fast and I mean fast resolder touch up and inspect all the pics areas shown. Those are all hand soldered imo pretty shoddy for 'denon'. I'm not too impressed with the audio stats on most of their stuff and complexity and available affordable service for the buck you pay for msrp.

 

[magreen]

I'm not sure of what in particular to take pictures of, but here are a whole bunch. There seems to be a resolution limitation to what I can upload, but I hope these come through. Thanks for looking.

Input board:

 

[magreen]

Power amp board: (harder to get a good shot of this)

 

[magreen]

Solder side of boards:
1:


2:

 

[Binkman]

thanx for the pics.. I'm not a photographer but i see gray and holes on many solder pads. IMHO ....Good pcbs just not good joints. Again... get a good magnifier and resolder more than the few i reviewed. I see gray or 'grey' and not good when photos show darker grey and center stems of components. lighting. hole in the middle.and I can see the component lead with a hole in the center using my browser magnifier. "cold joint".

Fast and I mean fast ! reflow on suspect joints as I think this unit has been repaired but soldering not good. Sorry best I can explain it.

 

[magreen]

Great. Sorry to be a bother, but would you mind highlighting a couple of examples of what you mean for cold solder joints? That way I'd have a visual example to go with your very helpful descriptions. Thank you! Also, do you think these could account for the frequency response I've observed?

 

[Binkman]

https://www.google.com/?gws_rd=ssl#q=cold+solder+joint

 

[Karl vd Berg]

magreen, could you pls take another closer picture around the circled areas? These seem to be where the big caps are, and I see a "square" solder (red) pointed next to one of the cap leads. Did you remove that dark foam, too?

 

[magreen]

magreen, could you pls take another closer picture around the circled areas? These seem to be where the big caps are, and I see a "square" solder (red) pointed next to one of the cap leads. Did you remove that dark foam, too?

Here are better pictures of that area. I didn't remove the dark foam yet because it's on there really strong, and when I pull at it it starts to disintegrate, leaving material behind on the PCB.

 

[magreen]

Question: I see more than a few places where there appears to be a solder jumper, i.e., two adjacent pins connected with a blob of solder. I've looked at the service manual and it doesn't look like those should be there, but I'm not sure. Should there never be two adjacent pins connected by a solder blob?

 

[magreen]

Here's an example that I've marked up. Please let me know if I'm off target.

It seems to me the solder jumper indicated by the red arrow is unintentional but still not harmful because those are on the same trace. Is that right?

The green arrow seems to me to indicate a possible accidental jump to the pad to the right, to a different trace, which could be harmful. and the purple arrow seems to have insufficient wetting on the lead. Do I have this right?

This is a photo from the power amp section with/next to R3-R8

 

[magreen]

Also, I ripped off what I could of the black foam pad and cut through what remained using a thin plastic edge, just enough to reveal the other contact of C91. Here's a pic.

 

[Karl vd Berg]

At service manual PCB layout, it seems the caps have some space - so no other components surrounding them. The pads where the positive leads go should not be changed, only the negative ones to new holes in a (safe) position where they meet - within ~10mm - their traces by rotating/shifting a bit (2nd pic, blue lines).

Removing that part of dark foam in between leads a bit can tell if you can reach the traces within 10mm. I reckon this may not be that easy at first time, but this is an idea if new caps of 30mm diameter and 14.4mm lead spacing cant be found...