Denon Amp Repair

[Oldman79]

Hi Guys

I have a Denon AVR-1909 that has failed.
I think I have diagnosed the issue down to the standby transformer (it is open circuit on the primary side) but the issue I am having is where to source a spare part, anyone know a place that could help me out?

[shakalnokturn]

Most often open transformer primaries are due to the integrated thermal fuse.
The fuse can sometimes be spotted, accessed and replaced by cutting a bit of plastic away from the winding connection tabs.
In some cases there are even connection tabs before and after the fuse.
I do not recommend however running the amp without a thermal fuse.

[Oldman79]

Interesting... I'll take a look

[mzacharias]

Small standby transformers have no fusible link. The fine wire of the primary IS the link.

[shakalnokturn]

Small standby transformers have no fusible link. The fine wire of the primary IS the link.

Maybe not all...
Have you torn any apart to check? I have, and I've seen more than one with primary fuse, sometimes thermal sometimes not.

[xavier60]

These small transformers have very high primary resistance and could be mistaken for being faulty.

[bob91343]

Even without a fuse, an open winding could be repaired with patience and some good tools.

[TheMG]

Small standby transformers have no fusible link. The fine wire of the primary IS the link.

Not in my experience. The great majority of small mains frequency (50/60Hz) transformers that I've seen do in fact have a thermal fuse. This is often done as it is somewhat more difficult to protect such small transformers from a meltdown with a regular fuse due to the low amount of current drawn and the high impedance of the primary.

The winding wire itself won't normally fuse open until it reaches a very high temperature. By the time that happens it could have gotten hot enough to release some magic smoke and present a potential fire hazard. Thus the integrated thermal fuse.

Unfortunately sometimes the thermal fuse can let go for other reasons, such as the unit being operated in a very warm environment (enclosed A/V shelf for instance), too high line voltage, or even just thermal cycling.

[floobydust]

I've seen many small 50/60Hz mains transformers have no thermal fuse, yet the winding melts at the bobbin terminals where the flying leads connect. The winding is the fuse. Copper melts wherever there is the most thermal insulation and can glow hot, so not within the winding.
But, to be clear there are gross overloads that melt the winding almost instantly, or moderate overloads say 300% of rated where the transformer heats up and smokes for a while until the winding shorts.

I've done surgery on a few transformers but it's almost hair fine wire and pretty tedious.
OP might have a 120/220V issue, a mains surge or corrosion from very old flux at the pins, that cause the open circuit.
I would hit up Denon for the part 00D9630387602 (US/Canada 120V) looks around 9VAC.

[mzacharias]

I've seen many small 50/60Hz mains transformers have no thermal fuse, yet the winding melts at the bobbin terminals where the flying leads connect. The winding is the fuse. Copper melts wherever there is the most thermal insulation and can glow hot, so not within the winding.
But, to be clear there are gross overloads that melt the winding almost instantly, or moderate overloads say 300% of rated where the transformer heats up and smokes for a while until the winding shorts.

I've done surgery on a few transformers but it's almost hair fine wire and pretty tedious.
OP might have a 120/220V issue, a mains surge or corrosion from very old flux at the pins, that cause the open circuit.
I would hit up Denon for the part 00D9630387602 (US/Canada 120V) looks around 9VAC.

I have seen MANY on which the primary winding was blasted - no thermal fuse or other element.

This applies to Denon, Yamaha, Marantz, Pioneer, Onkyo, Sherwood, and other modern receivers and amps using small standby power supplies.

[Haenk]

If it's only a standby-transformer, an older cheap 9V wall wart might be a good source for a replacement; there probably is a voltage regulator anyway, so something with a wattage and voltage around the original part should be fine.
In case the original part is no longer available or prohibitive expensive or you want to keep repair costs down...

[wraper]

I doubt it uses regular transformer for standby, not SMPS.

[Haenk]

https://www.manualslib.com/manual/815424/Denon-Avr-1909.html?page=161#manual

I'd say SUB501 is a simple and small single-voltage transformer going into 78R05, so that wall wart transformer should be fine. (Of course that's no "nice" solution, but it's easy to find and crack open for parts...)

[Oldman79]

Thx all for your input.

I can confirm that it has no thermal fuse and the standby transformer has burnt out for sure.

I have since hooked up a variac and set it to 12V in place of the standby transformer, this restored the 5V rail but the amp didn't come back to life. I still have no +15V or -15V, I dont even have voltage going itno the 15V regulators.

[shakalnokturn]

Variac and isolation transformer?
I second Haenk, throwing a wall wart in there even as a temporary solution is less scary than a Variac.

With 5V supply back, does the amp switch RLY501?

[shakalnokturn]

I couldn't find the information with much certainty, check coil voltage marked on RL501 itself, if coil voltage is 30VDC your 12VAC input won't be enough to switch the relay and bring the main supply up.

[mzacharias]

I doubt it uses regular transformer for standby, not SMPS.

Small conventional standby transformer - not a SMPS.

[Haenk]

You probably need to check the parts in the lower left corner, a voltage peak might have damaged something (burning the primary winding is something…)
Maybe force RLY and check if the system boots up then.
(Following the diagram on the screen is wickedly complicated, grrr)

[Oldman79]

After further testing I have found that the primary transformer is not out putting on any of the secondary winding's. At this point I think I will have to bin the Amp as finding a replacement power transformer for an amp of this age will be near impossible.

Thx to all for your input

[shakalnokturn]

If you have checked that line voltage is actually reaching the main transformer. Measured primary windings and found at least one to have gone open. You could still try and find an embedded fuse in that transformer, easier because bigger.
There are spare transformers around (eBay) depending on how much you value your amp.