Marantz Pm350 Pt1 Fault diagnosis.

[@ovalwingnut]

Fantastic 👍😁 Especially loved the +speaker thump tip. Thank you

[@AverageJoe2020]

I like the way that the tone board assembly is stitched together with link wires to allow soldering on one plane, nice. Best regards, J.

[@Andrewausfa]

I was thinking exactly that, spiral bound boards.

[@peterjmcgee4680]

I stand corrected I admit when I'm wrong usually when that happens to bed final output transistor now I learn something new on certain amplifiers they have to check the preamp for that symptom

[@Andrewausfa]

I'm getting bored fixing radios, I feel inspired by your videos and may have to find an amp to play with. The ones I come across at boot sales are mid-80's black face things that may be worthy of tarting up but just look bad.

[@SoddingaboutSi]

I like some of the black year from the 80's Andy but lots of them have those horrid Hybrid chips that are rare as rocking horse shit. Look out for an olde British Leak or Armstrong maybe?

[@Andrewausfa]

Simon Spiers I've got a Leak Delta 30 in the loft I think

[@SoddingaboutSi]

Andrewausfa Up you go then Andy :-)

[@MrDubje]

Love this kind of videos from you, they are a pain to do though. I guess there are some bad capacitors on that board as well, the small electrolytics should be dry as a bone after all those years.

[@SoddingaboutSi]

MrDubje The caps are like new. They only tend to get dry if they are exposed to heat.

[@MrDubje]

Didn't expect that, usually I found even the best ones do age a bit. Perhaps the new old stock from work was stored in a hotter environment or are not representative in general.

[@TheDefpom]

Nice diagnostic work.

[@SoddingaboutSi]

Cheers Scott

[@micinum]

Something weird is going on with my amp (same model as this). If you listen to low volume levels it is ok but on nornal or just a little loud one speaker will lose sound but slowly it will turn dows (and while it turns down it will have distortion) and completely lose sound. If you turn off thr amp wait a couple of min and turn it on it will work...any ideas on what can i check. Everything looks normal and it is not blown. The preamp is not the problem because i have made a button to go directly to the amp without the equilizer (preamp)...

[@peterjmcgee4680]

The minute I saw that woofer bulge out and heard that hum it's got to be a final output transistor and it's definite DC to the output just got to be a final output very rarely is it a preamp or a driver that's doing that that's going to be a final output transistor that shorted

[@mdzacharias]

Wondering about the +15 volt supply and the obvious possibility of bad solder connections where the two tone boards are folded over. The whole board looks toasty too - those caps don't look too good either.

[@SoddingaboutSi]

+Mark Zacharias What's wrong with those caps?

[@mdzacharias]

I just though they looked a little cooked.

[@SoddingaboutSi]

Mark Zacharias They are audio coupling caps that have next to no voltage on them. This amp is very low powered and runs cool. All caps have low esr and leakage. That was one of the things I checked with the scope to see if they were failing.

[@mdzacharias]

The ones on the tone board?

[@SoddingaboutSi]

Yep the electrolytic's. Polyesters were to expensive and large in the 80's to fit this application.