Denon 3808 - No Display / Audio Output

[crashp3]

Hey Guys:

Got an interesting one the other day off of Craigslist. Picked up a Denon AVR-3808CI off of Craigslist the other day. I currently use the same model for my home theater system.

In anycase, he stated it was dropped during a move, and since then, the front display wouldn't light up and it wouldn't output sound.

Took it home and tore it apart, was dropped on the front left of the reciver (by function knob and transformer), there was a small crack to the function knob PCB and knob selector was damaged, repaired the knob and verified all traces were in tact on the PCB, all was well!

Powerd on the unit again, there is no display and it doens't output any sound through any of the terminal connectors, in fact, the main transformer doesn't seem to kick in at all.

The unit otherwise works flawlessly, it comes online on my network, I can adjust any of the settings via the webGUI (input, etc.) and it does output video, so it appears all the main circuitry is working fine.

Looking at the service manual, the front display is also powered by the main transformer, not one of (2) secondary (smaller) ones.

Is there any easy way to test a transformer other than tearing it apart? Any suggestions?

Thanks!

[selldoor]

Re: Denon 3808 - No Display / Audio Output

Pictures might help I for instance have no idea what a Denon3808 looks like on the outside never mind the inside.
Any fuses to check? Transformers can be quite heavy has the fall cracked the
solder joints?

Can you update your profile with country and mains voltage.

[crashp3]

Re: Denon 3808 - No Display / Audio Output

Updated my profile. Sorry for the poor pictures, my good DSLR is at the shop currently for repair, so I had to use my Android phone.

I can upload more photos if required, and also have the service manual/schematics if it'd be of any assistance.

The drop was significant enough to slightly bend the chassis on the front left, the main transformer sits about 6" behind where the chassis bend occured. The receiver weighs a good 50 lbs, majority of the weight is on the left side (where the transformer is), so I wasn't surprised it bent the chassis.

All fuses were checked, and all tested good.

Picture 1: Main Transformer. Wire leads on left of picture go to front panel
Picture 2: Power board to upper left - Amp section in middle
Picture 3: Picture of power board. Lower left is where the main transformer get's its power (red/black cable). Fuse is missing as I tested, and didn't put back in for photos.

Picture 4: Close up of power board. Main transformer plugs into white plug on upper right of picture

Picture 5: Another angle of power board
Picture 6: Another view of transformer

[tom66]

Re: Denon 3808 - No Display / Audio Output

More than likely there will be a relay and a circuit to switch on power to the main transformer. See if you can bypass this temporarily to get it to work.

[crashp3]

Re: Denon 3808 - No Display / Audio Output

Thanks Tom! Not sure if you remember me, but I was helping you with service manuals there for a while. Life got in the way of things and I had to put a ton of stuff on hold! If you need any service manuals, let me know... I'm back in the game

I still had the logon to your service manual site, so I am uploading the 3808 service manual, and 4308 (bigger brother) to it now


In any event, I'm likely over my head with your suggestion, attached is the powerboard schematic from the service manual. Are you able to assist in your recommendation?

CX023 is the wire lead (red/black) that goes to the main transformer that isn't powering on.

To note, the secondary transformer (CX025) does properly power on.

[tom66]

Re: Denon 3808 - No Display / Audio Output

Hi Crash, yeah, I thought I recognised the name RL401 is probably the main relay.

If you have any Panasonic service manuals, I'm interested -- I managed to get a few hundred off Panasonic's Chinese service site due to a leaked log in, but I haven't got some of the newer ones for the X/S/GT/ST/VT(30|50) plasmas etc.

[crashp3]

Re: Denon 3808 - No Display / Audio Output

Thanks Tom, I'll work on pulling this board out to bypass it, this is unit is packed like sardines and removing anything is a pain.

For reference, the relay is as follows:
DLS1U (model series)
6VDC 0.25w
TV-8 (model #)
5A/100A
3A/120A
250v
DEC (manufacturer)

Was trying to figure out a way to test the transformer out of circuit (by itself), but failed at figuring that out. Figured if I could atleast see if it powers on, I could trace back from there.

Quick google search didn't show any results, other than MCM Electronics' replacement part (Denon's replacement part supplier).

I'll work on those service manuals for you

[tom66]

Re: Denon 3808 - No Display / Audio Output

You can upload them to a Dropbox account to make it easier -- that uploader is still limited to about 7~8MB.

[selldoor]

Re: Denon 3808 - No Display / Audio Output

Are you getting 120 volts on the outlet CX023 and on the other end of the cable?

[crashp3]

Re: Denon 3808 - No Display / Audio Output

Are you getting 120 volts on the outlet CX023 and on the other end of the cable?

Thanks for the reply! Luckily I saw it before I tore the board out!

With CX023 (main transformer lead) plugged in, I do not get any voltage reading in standby or on "power on" mode - thankfully there was enough spacing in the socket to insert my probes.

However, when the transformer (cx023 wire lead) is NOT plugged in, and I connect my probes directly to the power supply pins (cx023), I DO get a steady 119/120VAC while in standby and power on mode.

So, in a nutshell, transformer plugged into power board = no VAC on the cx023. When transformer unplugged, probed directly to powerboard = 120vac.

Without tearing the transformer out and apart, there's no (easy) way to get my probes on the end of the lines that go into the transformer to measure for voltage. If this is necessary, I'll try to figure out a way.

Assuming this points towards the main transformer?

[selldoor]

Re: Denon 3808 - No Display / Audio Output

Looking probable - your sure it hasnt moved in the fall?
Does it have any soldered contacts direct onto any board or just via wires.
Can you post the part of the schematic with the main transformer on it.

[crashp3]

Re: Denon 3808 - No Display / Audio Output

Looking probable - your sure it hasnt moved in the fall?
Does it have any soldered contacts direct onto any board or just via wires.
Can you post the part of the schematic with the main transformer on it.

The transformer has 4 mounting points to the bottom of the chassis, all of these appear to be very tight and and have no visible signs of movement. The chassis, however about 2 inches in front of the transformer (ref pic #1, upper left) does have signs of bending, but does not appear to have impacted the transformers mounting to the chassis.

The main transformer itself is all wire leads, and the leads connect to secondary boards via socket connectors. Based on reading this, I disconnected EVERYTHING that gets power from the main transformer (amplifier boards, front panel display), excluding cx032 (trans voltage input) and the transformer still does not power on, and does not show any voltage readings at cx032 when plugged in.

Unfortunately, Denon doesn't list any schematics for the transformers itself. The individual boards that connect to it show the connects "to power trans" (ie cx023 on the schem. i posted) but there's no diagram what so ever of any of the transformers.

If it helps, I uploaded the full service manual here:

[tom66]

Re: Denon 3808 - No Display / Audio Output

This may be normal. The relay only interrupts one terminal, usually the live, but sometimes the neutral. Often the neutral is floating just a few volts relative to earth, but the live is usually much greater relative to earth and will easily pick up 120VAC (of course with very high impedance), even though the relay is off. Try a lightbulb across the 120VAC and see if it lights up.

A transformer is a coil of wire wrapped around an iron core. It's pretty rare for it to fail, and if it did, I'd expect a short between windings -- leading to a blown fuse -- or an open winding -- leading to no output, but with good 120VAC input.

[selldoor]

Re: Denon 3808 - No Display / Audio Output

With the power off can you test the primary on the transformer - start with meter on ohms
20000 and work up or down depending on what you find - what I am struggling with is when you connect it, it shuts down the input? yes? I would have thought that at 120v
if it was shorted it would blow the fuse? If it was open why would the power shut down?
Unless - what is that fl401? resettable fuse??


EDIT May not now be relevant - watching tv and forgot to press enter LOL

[crashp3]

Re: Denon 3808 - No Display / Audio Output

F401 is a typical cylinder fuse rated 10a/120v. The weird thing with this fuse, I suspected it to be bad at first as it is very smokey (not see through like all the other ones), but tested with a meter and does show continuity. Also ruled this out when I am getting 120v at cx023 when nothing is connected, am I mistaken to think that?

Tried hooking up a light bulb to cx023, light did not illuminate. Lightbulb + meter = no voltage. Removed the lightbulb, and tested the pins again, which still show 120v when nothing is connected.

Not quite sure I understand how to test the transformer? What's considered the primary side? Where do the probes go?

Tom: Figured transformers rarely go, but could a drop situation, significant enough to bend the chassis by the transformer, be a contributing factor in a short lived transformer?

The main trans is $114 (http://www.mcmelectronics.com/produc...09-/2330737009) and I'd hate to spend that without being certain

[selldoor]

Re: Denon 3808 - No Display / Audio Output

I dont mean F401 Imean FL401 at least i think that is what it says.
On the schematic extract you posted it is below and between the two
fuse holders. The primary side (winding) is where the mains goes in (in this case)
You are probing the same contacts as when you tried to measure the voltage.
REMEMBER POWER OFF.

[tom66]

Re: Denon 3808 - No Display / Audio Output

The fact that the lightbulb didn't come on tells you whilst there may be voltage, it can drive very little current (in other words, it is high impedance.)

It's not a bad transformer. You'd have a blown fuse, or 120VAC on the primary and no output. But even that would be very rare.

So, for some reason the relay isn't coming on.... and I don't yet know why, but bypassing it may show the rest, including the transformer, is working.

[crashp3]

Re: Denon 3808 - No Display / Audio Output

I dont mean F401 Imean FL401 at least i think that is what it says.
On the schematic extract you posted it is below and between the two
fuse holders. The primary side (winding) is where the mains goes in (in this case)
You are probing the same contacts as when you tried to measure the voltage.
REMEMBER POWER OFF.

FL(ActuallyRL)401 is the relay Tom was mentioning above.

Probes on the primary winding, meter set to OHMs, all meter readings show a value of "0", except on the 200 and 200M scale, which fluctuates between 0.8 and 1.0 value

[crashp3]

Re: Denon 3808 - No Display / Audio Output

The fact that the lightbulb didn't come on tells you whilst there may be voltage, it can drive very little current (in other words, it is high impedance.)

It's not a bad transformer. You'd have a blown fuse, or 120VAC on the primary and no output. But even that would be very rare.

So, for some reason the relay isn't coming on.... and I don't yet know why, but bypassing it may show the rest, including the transformer, is working.

Thanks Tom, I'm going to work on pulling out the powerboard. There's a ton of wires, and (3) boards that need to be removed to pull the part out to bypass it.

Since that fuse passed continuity tests, despite being very "smokey", should that be an area of concern at this point? Every other fuse in the receiver is nice and clear where you can see the filiment.

[tom66]

Re: Denon 3808 - No Display / Audio Output

Could just be dust. Also be wary of some meters with continuity. Often show it for far higher than you expect. Retiredcaps says some do it at up to 1,800 ohms!