Denon audio receiver. Hit by lightning while in standby. Puzzled with PSU.

[fastline]

I am messing around with an old receiver that has received a surge from lightning somehow. There are no obvious signs of damage, no blown fuses, no odor.

I have the service manual and combing the circuits for minor issues first. I have enclosed the CPU circuit and the PSU circuit. I cannot determine what is power TO the CPU and what is power being sent FROM the CPU.

The basics of the circuit as I understand it is the "P. SW" is the master switch on the front that allows the standby systems to function. This is a mechanical switch and works as it should. When it is enabled, the "on" switch has an LED surrounding it which also functions as a warning indicator. Red or flashing would indicate problems but it stays solid green. When the "on" button is pushed, it does nothing. I am not quite sure yet where this "on" switch goes or what it does, if the CPU stays powered all the time, or what.

There are two mechanical relays that latch up a couple more larger transformers when the unit would switch on. Those relays never turn on. I need to determine how to troubleshoot the circuit. There are 12 traces from the PSU to the CPU. V protect, GNDs, M6V, CPU/E PWR, etc. I cannot make heads or tails of this....? It looks like the Vcc or CPU power is 5V from another source. What is the 6V?

I ultimately need to determine if power is sent FROM the CPU to the relays to power up, or if the "on" switch simply fires up the relays, which further powers everything else, including the CPU?

As of right now, none of those 12 lines produce reasonable voltage IMO. A few are about 1.7V, but no 6V or anything higher.

 

[fastline]

UPDATE: Sorry, after digging into the manual more, the CPU is clearly spec'd out and appears that it is powered all the time and is receiving power because it send out the "green LED" signal to the standby light on the front. The CPU also sends a RED LED signal when there is an issue. I think the red LED will flash, etc if there is a problem but the green is solid and never changes state.

There is also a "main power" line from the CPU and indicates this is the line output for the main power relays to fire up the receiver. The issue is this appears to go to the front panel switch, not the relays as I expected. I also sort of lose the line a bit because of how they drew the schematic. Trying to sort it now.

 

[fastline]

Further, I should have probably read more...... I rarely find much use for the troubleshoot sections but this one clearly points me right to a 6V PSU IC if there is not 6V present on the M6V pins during standby. I do not have voltage on those pins. Hoping that is all of the issue..... At least the CPU seems to be getting power and not tripping out.

 

[fastline]

Update: Looks like the IC501 is good. This is the 6V regulator working off the standby transformer. It is making a nice 5.997V and then 5.6xxV at the CX126 connector with everything unplugged. By connecting nothing but the CX126 connector in circuit, that voltage drops to 3.0V. So does this look like a short somewhere on the 6V rail? Still not really sure what this even powers. My luck though, that reg was easy enough to get to.

 

[vtech]

I used to deal with Denon for many years and I can tell you that when it came to a true lightning/surge damage, it was NEVER straightforward regardless of the AVR or AVC series. Almost always, the main problem is somehow related to the standby power circuit that is incorporated on majority of their receivers. As you have noticed, when it is plugged in to AC, the standby power is always powering the CPU in standby mode waiting for an on command.
Any surge, can do a LOT of damage within the unit---some of which may not be apparent at first.
I can literally write a book about the subject as I have seen my share of it. As a rule of thumb, if any of your valid supplies, is pulled down, get ready to find short(s). Anything in the CMOS switching or even a single port on main processor or EPROM etc. For example, any of the Mitsu. Mxx series or NEC UPDxx series of processors were easily damaged. Even if/when you get the unit operational, don't be surprise to see other issues down the road.
Denon has always had a High End moniker in the consumer audio. Certainly a refined look and perhaps better sound/features.
However when it comes to servicing, in my past years of experience, it has got to be one of the absolute worst, especially when dealing with lightning damage. As you will notice, control and power circuitry tend to be way over-engineered for basic tasks which can easily translate to nightmares.
Good Luck

 

[fastline]

Thanks for the reply. Just out of curiosity, I used the thermal camera on the circuits to see if anything stood out. There are a few warmer areas on the CPU board but one thing that really stood out is ZD501 on the CPU PSU board. I meter tested the zener as good with .7v drop. The diode does not warm up until the master switch is on which turns on the standby systems.

As well, this diode does not heat up at all with the supply disconnected from the CPU board.

Do you think this instant heat level is normal for the diode or would this indicate it is throttling current due to a short and getting hot?

 

[fastline]

Grr.... I suspect vtech may be right on this one. The thermal image shows the CPU chip. tracing things out and following the heat signatures, R155 on the CPU board diagram is pumping some heat. From the PSU, the 6V goes through only 1 diode, then to the R155 on the CPU board, then another diode. This effectively drops the voltage seen at the chip at 5V and it is further used in multiple circuit at 5V.

Pin 99 on the CPU is the leg going to the M6V from the supply and that leg is also showing a short to ground. I might otherwise wager it is something else but the chip is obviously getting hot and I would think if it were something else shorted, it would show up on the thermal. ??

As well, the zener "ZD501" on the PSU is getting to about 130F! Is that typically a normal situation for a zener holding things back at no load or is this being caused by the shorts in the CPU board? I am having trouble understanding the function of the zener and why it is so hot.

 

[Nigel Goodwin]

As a professional service engineer I've dealt with countless lightning damage claims over the years, generally it's not worth the bother unless it's something simple and obvious.

Usually it's a continuous chain of different faults, you repair one and find yet another - I've done a few TV's (mostly as a matter of personal interest) and repaired 20-30 faults, only to find the tube was damaged as well

I don't know exactly what happens, but it appears to permanently deform the shadow mask, causing sharp edged purity errors.

 

[vtech]

Grr.... I suspect

I have been out of consumer electronics for almost ten years but reading all this sure brought back memories. All I can say is Dejavu.
As you can clearly see the heat signatures as being the loading spots. Normally you would continue on and try to isolate the shorts.
Trouble is more than likely you would be going down the path of several components to no end.
And just when you thought it was finally done, there will be more to show up.---believe me been there done that many many times.
I know that folks who spent extra on "higher end" equipment hate to let it go but for whatever reason Denon and lightning simply do not get along.
On a quick look, ZD501 is meant to provide a reference through R502 for a stable standby of +6V at the base of TR501 in the stand by mode.
Idea here is to automatically power down the unit back to standby if/when the incoming voltage drops below a specific level.
Problem arises when +6V line gets zapped (processor is definitely hosed). ZD501 survives the hit however, being the weakest link, it attempts to regulate the standby +6v line which is almost shorted through the processor(may be more)---hence the extra heat.

 

[fastline]

No biggy. I am sort of into audiophile goodies but this Denon was just a freebie. Hoped I could use it for a bedroom or something. Actually the guy tried to sell it to me but I knew it was a serious crap shoot. Lightning is the one word I don't want to hear.

I have been a fan of Denon sound quality from their AVRs but I run separate amps so I guess I more or less used one as a dead head. I run horn loaded speakers which find any digital noise, etc.

I switched to a Pioneer Elite AVR a while back. have not been too impressed. Not sure why I stick with the AVRs and use as a processor. I guess only because you get so much less guts in a preamp unit for the same price.

Recently repaired my parents Marantz AVR that was just a capacitor issue but I understand all the caps in it are junk so I am sure I will be back in it. Marantz otherwise has a nice AVR, IMO, soundwise anyway and build quality seems good.

Question - so with the heat signature of the MCU in the thermal, are we pretty safe to say the MCU is toast? Looking at the data sheet, I think that thing should be at about 100uA in standby.

One thing about the thermal images is you must look at the scale on the side to get an idea of dT. Sometimes the colors make it look worse than it is.

 

[vtech]

Sounds like you are in the quest to fix it!
As far as current draw goes, yes it should be in the milliamp range. Judging from experience, I can pretty much assure that your processor is gone. Lifting VCC pin(s) usually will bring the standby back---to what level, it is hard to tell. If you happen to luck out, it may be the only load on standby line at the moment and most likely would see a different heat signature.
I am very familiar with using the FLIR, as it is used almost daily on repairing aircraft related equipment at work.
One of the most useful features is the ability to save the complete signature from a known good board and use it as a reference. Even with audio narration!
Going back to the Denon, another major issue is unobtainable replacement parts--especially if it happen to be an older unit. Many of the model-specific processors have long been discontinued and chances of finding them were next to impossible when I was active in the field.

 

[fastline]

Na, I doubt I will move further with the unit. Just wanted to make sure the processor was gone before calling it a loss. It might be different if (all) it needed was a processor board. I might score one used but sounds like I might just chase my tail with other failures.

On a related subject, I am curious about proper surge protection? Reason I ask is the "Monster" brand has been very popular with big box stores. Monster cable, Monster power, etc. However, I found interesting reading years ago that they are mostly fluff and crap. I have some of their equipment that I got in an auction lot. I repaired most of it but not too impressed. A rack of MOVs for $500? I also have one of their "voltage regulators" which is an processor controlled auto transformer. What purpose it serves is silly. Monster quote, "for the best reliability of your TV, you need a precisely controlled 120V at all times".... So 118V will make my TV blow up. The BS on their surge units says "clean power" all over them yet I cannot find much in them that do any sort of filtering.

In short, I question if these WAY over priced devices are any more than what you get in a $20 power strip with surge protection. BUT, what is out there that can really protect expensive equipment?

 

[Nigel Goodwin]

Reason I ask is the "Monster" brand has been very popular with big box stores. Monster cable, Monster power, etc.

It's popular with the big stores because it's VERY high profit margin for them - but generally it's vastly over priced crap - NEVER buy anything with 'monster' in the name.

Most protectors do very little, but 'may' provide a little extra protection over nothing - it really depends how much you want to spend, but generally a good level of protection costs more than it's likely to save.