Modifying DENON POA-1500 from 220V to 240V. - Page 1
Forum section: electronics / projects

author: Sören_Marodören
author_rank: Contributor
timestamp: July 20, 2025, 04:32:16 pm
content: Background:Recently I had the opportunity to repair a DENON POA-1500 amplifier.The main issue with it was that all the bulbs on the VU-meter (6 x 28V/40mA) + the one illuminating the DENON-logo was broken. According to the owner, the bulbs didn’t last long.Googling the problem also indicated that this is a common problem.The 3 + 3 bulbs for the VU-meter are according to the schematics powered from a +25.5V supply and grounded via two transistors of the startup sequence is finished. (A previous owner has modified this unit and removed the transistors and placed the bulbs 3+3 in series. This only made them glow. Didn’t look nice.)On Ebay (search for “Denon POA-1500 Lights Service Amplifier Update Repair Kit MDK 15001 Instructions”) I found a kit with 10 new 28V/60mA bulbs together with two transistors (2SC2655) and two 4.7 kΩ resistors. According to the seller, this is an update kit similar to #MDK 15001 from Denon that shall solve the issue with “…premature light bulb burnout and other issues”. I ordered a few of these kits.Investigation:When the kits arrived, I removed the mod mentioned above and mounted the new lamps (60mA instead of what ever was mounted there). I also mounted the transistors (2SC2655) and one of the resistors. I wanted to see if a change from 15 kΩ to 4.7 kΩ was going to make any difference.When testing this I noticed two things:1) Lowering the resistance did not have any impact to current and voltage to the lamps. The transistors are saturated in both cases. (I keep the original 15 kΩ.)2) The voltage to the lamps was on this unit 28.5V! According to the schematics it shall be 25.5V.Hmmm, this isn’t right.After having a closer look at the schematics, I see that there are four international variants of this POA-1500 depending on mains voltage in the country/region.• USA/Canada: 120 VAC.• Hong Kong/Singapore: 110, 120, 220 and 240 VAC, selectable via a switch.• Europa: 220 VAC.• England: 240 VAC.The unit I’m working on is a European 220 V. Here In Sweden, we have since many years 230 VAC and where I live it is often >237 VAC. Measuring the internal voltages indicated that all were too high. The voltage to the big main capacitors (33000µF/71V) had a voltage at 69 V. A bit too close to the rated voltage to feel safe.With a unit “hardwired” to 220 VAC there seems not to be a good solution for this problem.When I looked at the P.S. UNIT (ETC-627-6) at the inside of the rear panel I noticed two labels with the text “220V” and “240V” on them. See first picture.On the bottom of that PCA I can see that the blue wire is any ware. It seems to be placed there as a spare in some odd way. But I was not sure.And the 240V label made me think that maybe we can fix this by just swapping the Yellow and Blue wires… But I need to test it in a controlled way first.Test:Measuring the resistance from the White wire (coming from the switch) to the Yellow resulted in 2.06 Ω and to the Blue resulted in 2.26 Ω. Probably a good indication that my theory is correct.Next step was to use my variac and test how the output voltages from the transformer behaves when I apply different low voltages to the Yellow and Blue wire.Test at 13.9Vac in to Yellow wire: 68V-supply at 6.02V.Test at 13.9Vac in to Blue wire: 68V-supply at 5.49V. -> A reduction by 9%My theory might be correct… I crank up the AC to 237 VAC and test that too:Test at 13.9Vac in to Yellow wire: 68V-supply at 102V.Test at 13.9Vac in to Blue wire: 68V-supply at 93.9V. -> A reduction by 8%A test on the light bulbs show that the voltage is reduced from 28.5 Vdc to 26.5 Vdc, which I think is acceptable when running at 237 VAC in.I swapped the wires and it now looks like this. See second picture.Conclusion:If you have a European DENON POA-1500 and experience issues with bulbs that burnt out too fast it can be a good idea to swap the Blue and Yellow wired on the P.S. UNIT at the inside of the rear panel.

author: Vovk_Z
author_rank: Super Contributor
timestamp: July 20, 2025, 05:26:08 pm
content: Hm, "To swap wires"?But, accordingly to manual at the back panel there is a voltage selector switch. It has '240V' position.Possibly, that's a switch whose wires you swapped.I attached a screenshot and a full service manual pdf.

author: Sören_Marodören
author_rank: Contributor
timestamp: July 20, 2025, 05:47:15 pm
content: The switch is only available in the Hong Kong/Singapore version of the amplifier. See attached picture from service manual.The amplifier I worked on didn't have that switch.