Yamaha RX 500U Checkup (Ep. 145)

[@mdzacharias]

Yamaha's variable loudness works thusly: With Loudness control set flat, adjust volume with the volume control to about the maximum you would normally listen to, then use the Loudness control to reduce to your desired listening level, the low and high frequencies will be compensated accordingly, more correctly than a conventional loudness pushbutton.

[@SergZak2023]

Always a pleasure to watch your level-headed and calm approach to repairs. Keep up the great work Trevor! Thank you for taking the time to record and post great quality content.👍

[@TrevorsBench]

Thanks Serg, Nice to hear your feedback on my vids. Stay tuned for more

[@kevinrempel4059]

These are my favorite amps all because of the loudness knob. Its not the same as the volume. It lets you change the sound depth for every genre within seconds. Its incredible

[@craigm.9070]

I always enjoy your attention to detail; it's always the little things that make a difference. This little tune up should serve the owner well for years to come. thanks again for your time!

[@ggeter]

I've got one of these in my closet that I bought brand new in 1988 or 89. Plan on repurposing it in a home office. This will be very helpful as I recondition if needed. thank you!

[@jubemarsh2202]

Excellent as usual! 💯 You make taking apart pots look easy! 🤙

[@mikewillegal682]

My unit smoked about a year ago. I was able to debug and repair it without completely removing the front panel, which would be a major pain. The silastic goop that was supposed to stabilize a capacitor had etched trough a trace on the circuit board. The result was several burnt out transistors and a hole in the circuit board. I have posted several KZbin videos on the process I took to repair it.

[@TurntableGuy]

I picked one of these up recently with no relay click. Had a leaky transistor in one of the channels and boy was that hard to find. Now it has a channel imbalance (left is much louder than right). Anyway, that's as far as I went.

[@alexismethenitis]

Thanks for another great video.

[@greyfreeman5537]

Cool!! I'm trying to fix one right now!

[@poormanselectronicsbench2021]

A large surface area, and good air flow on a heat sink is a good design. One with more mass will take longer to absorb and transfer heat away from the components needing to be cooled. Many a computer CPU cooler have a large amount of thin fins that can dissipate heat quickly ( I have a few with a "heat pipe" and central fan set up that work very well) Hope that the servicing gets it back into good shape.

[@paulb4661]

One with larger mass will take longer to change its temperature as a result of the absorbed heat, but the heat transfer itself is a function of the thermal resistance of the IC/sink interface and heat conductivity of the latter only. One could argue, that a high thermal inertia of a large, preferably copper sink, will result in lower mechanical stress and slow down temperature changes in response to absorbed heat, thus providing a stable environment for the temperature sensitive output transistors.

[@poormanselectronicsbench2021]

@@paulb4661 One could see where, more mass to a heat sink would afford some "thermal regulation" , but as long as the components temperatures are kept within reasonable tolerances, both types of heat sink designs should work acceptably. Most audio output transistor heat sinks on larger amps are fully exposed on the back side or sides of the unit, so, you definitely would not want to put a fragile, thin finned heat dissipation assembly there, and the fact that he noticed that interior mounted assembly getting warm quickly means that it was doing its job well by moving heat away from the components and to the fins to dissipate it with a larger surface area. I guess most are just use to seeing that "old school" heavy aluminum finning.

[@paulb4661]

@@poormanselectronicsbench2021 At no point will the temperature of the actual devices have been lower, than that of the sink itself, therefore they will have heated up quickly and, respectively, cooled down fast upon lowering of the output level. This is a polar opposite to large heat capacity and slightly lower dissipation afforded by classical designs, where even rapid changes in output level result in moderate and delayed change of temperature of attached devices, thus maintaining nearly constant working conditions.

[@poormanselectronicsbench2021]

@@paulb4661That would be the difference between a larger massed "sink" design, and a "radiator" . A short term need to dissipate heat is handled in a more controlled manner by a sink design, where, an extended increase in temp is handled better by a larger surfaced area "radiator". The bottom line is, if this was such a bad design, it would have induced a chain of failures in any device it was applied in. It seems to work well for this application, and Trevor did not have to replace any final output transistors, so, it seems to be doing it's intended work.

[@paulb4661]

@@poormanselectronicsbench2021 What I was trying to point out was that a high mass heatsink does not take longer to absorb or to dissipate heat, because that's simply not true. Heat dissipation, conductivity and capacity define all parameters, but cannot possibly conspire to result in the action implied in second sentence of your initial post and in fact to the contrary, as high capacity sink would maintain large temperature difference between the IC and itself for longer in case of impeded heat transfer, but with the usual low thermal resistance of the interface simply keeps it cool for longer. Imagine having two identical kettles side by side, one quarter full, the other filled to the brim. Which one will boil first ? Does it mean it's more efficient at absorbing heat ? The only advantage of the sink featured here is cost, pure and simple. Please note also, that with low bias, class AB designs, the highest heat dissipation takes place at between 1/3 and 1/2 of nominal power output. With 120-250mA bias per pair, common in lateral mosfet designs bordering on class A for example, the sinks run hot at idle and actually cool down as the power output increases.

[@Poppinwheeeeellllllieeeeez]

After watching this video I kept my eyes peeled for one. Today I bought a mint condition example for the grand total of $20 Canadian. The volume knob was a touch loose and it needed a micro squirt of f5. I tweaked the case nut and am very impressed with it. A huge score. I was expecting to do some work to it. Nope. The pots were not even crackly. Sometimes you win.

[@TrevorsBench]

I had the pleasure of listening to this Yamaha for a while before I sent it back to the owner. Sometimes everything works as it should, nice score

[@nancybrummer5451]

nice one, thank you

[@frankgeeraerts6243]

Base extension is another name for some Loudness function ...

[@frankd.4528]

I have one of these and the “protection relay” won’t click in. Is that a difficult DIY?

[@cien0000]

Hi ! I saw one without the remot for 45€ , can i go for it?

[@mihaibalint8183]

Hi, I just found your channel, I'm killing my self with a Fisher ca915. Had to change a few components, amp works fine but keeps shutting of after 2 seconds, not more nor less. amp has idle current ok, no dc on output, cheked every power supply and they are good in a margin of 5%, and still does this. there are more details that I cant write down here. Can I get in touch with you personally? I'm from Spain and can't find technicians that go so far and deep inside old electronics. I'm kind of alone, and need some help. thx

[@TrevorsBench]

Hi Mihai, I can't find any info on the CA915 so I'm working blind here. Sounds like it wants to be in protect mode. Lots of things may contribute but the most obvious is a bad power supply. I would suspect one of the regulated supplies to be missing or bad. If you can find documentation please check all the power supplies for proper voltage. Aside from that, one of the amplifiers may have a problem with the input or voltage amplification stages. That could be tricky to track down without schematics. It's not something I can troubleshoot through emails because I'd need to see the amplifier to test it. Sorry I can't help you out more than this right now

[@josephlalock8378]

caps that are known to leak but they are not YET so you leave them? i'm outta here. good luck.

[@TrevorsBench]

Yes

[@Poppinwheeeeellllllieeeeez]

The biggest hit in 1987 - Walk Like an Egyptian. This is a prime example and all the more reason to learn how to service your own gear. I use silicon damping fluid 500 000 weight to restore feel to pots and Lpads. I got ripped off 12 years ago by a shitty Vintage audio shop in Calgary. Beat up an ADC 3 mk 3 sound shaper parametic equalizer. That was motivation enough to learn how to service my own equipment. Then I got addicted to servicing items. Like an adult puzzle. I love it. Who needs soduko? I always run a external cpu fan sucking air out. PLAY A TUNE AT THE END WILL YA! youtube track would suffice.

[@TrevorsBench]

True, fixing things is a great mental exercise plus you get the satisfaction of fixing it yourself, something not many people can do