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Denon POA-1500 lighting
- Thread starter rickflaherty
- Start date
Yes, I still have a few 5002's with meters and LED's, they don't even heat up in heavy home use, what an efficient design, back to the thread here, Dave.
Something not right after the lamp upgrade
I bought the 2SC2655 transistors and replaced the 2SC1815 according to the upgrade instruction, together with the new lamps 28v 0.06A. But when I turned on the amp, the meter windows lighted up very very dim... from 12 feet away it looks like there was no light at all. Only up close about 1 or 2 feed to the amp I would see the light from the meter windows. I checked and sure enough all 6 lamps for the meters are lit. But they are very very dim.... I measure the voltage at the plug that the light boards plugged into the amp and I got only 14 volt ??? Since the lamps are rated at 28v, I expect the voltage must be at least 24v or so. Something is definitely wrong with my amp. Does anyone have any idea?
I bought the 2SC2655 transistors and replaced the 2SC1815 according to the upgrade instruction, together with the new lamps 28v 0.06A. But when I turned on the amp, the meter windows lighted up very very dim... from 12 feet away it looks like there was no light at all. Only up close about 1 or 2 feed to the amp I would see the light from the meter windows. I checked and sure enough all 6 lamps for the meters are lit. But they are very very dim.... I measure the voltage at the plug that the light boards plugged into the amp and I got only 14 volt ??? Since the lamps are rated at 28v, I expect the voltage must be at least 24v or so. Something is definitely wrong with my amp. Does anyone have any idea?
Classic_CJ
Well-Known Member
Did you also change the two base resistors on the transistors? Resistors R101 & R102 must be changed from 15K to 4.7K. If you still have the 15K's in place it may not be fully turning on the new transistors. The schematic shows 25.5 volts sourcing the lamps (3 to each meter), each meter set turned on seperately by one of the two transistors, which ground the other end of the lamps when switched on.
If you are reading 14 volts, yes, something is wrong.
Classic_CJ
Well-Known Member
No, not that it should matter in this usage if there were. They are used as switches, so as long as there is enough base drive to turn them fully on (saturation), they should work.
Is the part number marked right on the transistors? The 2S prefix is rarely there, but you should see "C2655" or somesuch.
Thanks for the reply CJ, I did changed the resistors R101 and R102 to 4.7K value. You mentioned that the jobs of these two transistors jobs is to provide ground to the lamps, the other connector to the lamps should always has 25.5 volts. My lamps did turned on, meaning the transistors are doing their jobs, right?. Maybe the source of 25.5v is not providing enough voltage?
One thing I notice that when I first turned on the amp, the voltage at the lamps is only about 12v, then it gradually go to 14v then stop at 16 volt (I just measured again). Is this gradually going up voltage normal?
My 'bad'.... really bad... I just double-checked everything and realized that I used '47k resistors' instead of 4.7k as you suggested... (I am realizing that I am old now). I hope it did not damage the transistors. They were running quite hot. I will run to Radioshack to get the 4.7 resistors and use them tomorrow morning and report back the result. Thanks CJ
Classic_CJ
Well-Known Member
Not so young myself anymore (57), so I know the feeling. The higher ohms value on the base resistors you put in could certainly explain what was happening. You may have damaged the transistors if they were very hot for an extended time period. Did you get only the two you needed, or any extras? If you got extras, I would change them even if the lights work OK once you have the correct value resistors in place. If not-- wait and see.
Good luck!
It works .. CJ... The meter windows now light up very nice and the transistors don't run hot anymore, I will change them (the transistors) anyway as you suggested since I bought a pack of 10 of them.
Tonight I finally have the set PRA-1000/POA-1500 both are fully functional and work perfectly. Thanks CJ...
rickflaherty
New Member
Thedo,
Did you find something in a good replacement binding post set-up? The stock stuff is a block of eight that doesn't accept bananas.
Did you find something in a good replacement binding post set-up? The stock stuff is a block of eight that doesn't accept bananas.
Yes, I agree that the non-banana accomodation is very inconvenient. I have not found a way to get around it yet as you already know that the original posts come in a block of 8 posts. I will post whatever I find or think of in this thread.
Henry
rickflaherty
New Member
Good deal. Thanks for the consideration.
rickflaherty
New Member
Thedo,
I found that these work: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=091-1140 &FTR=091-1140
If you screw out the old thumb knobs, you can take the little nut off these and screw them righ in where the knob was. They stick out a bit, but they work.
You don't even need to take off the rear cover.
I found that these work: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=091-1140 &FTR=091-1140
If you screw out the old thumb knobs, you can take the little nut off these and screw them righ in where the knob was. They stick out a bit, but they work.
You don't even need to take off the rear cover.
Rick, thanks for the tips, I will do it sometimes.
Below is the link to some pictures of my PRA-1000 and POA-1500
http://www.audiokarma.org/forums/showthread.php?p=4140005&posted=1#post4140005
Rick
I could not screw out the old thumb knobs? they stopped at the end and I'm afraid if I used more force I would break them. The service manual did not show them separated from the whole speakers block.
How did you manage to do it? can you post a picture of the post after removed?
Thanks
rickflaherty
New Member
Hi Thedo,
The threads on the thumbs are upset at the ends, so that they are self retaining. What I did was to unscrew them (top row first-of course), first by hand and then with a pair of needle nose. Then, I tightened the nuts against the lock washers of the new units and took the small jamb-nuts off.
Start from the bottom row and thread on the new units. Torque them down (not too much) with the pliers.
I didn't strip the female threads of either of my POA-1500s (16 places). So you shouldn't have a problem.
I am planning a better upgrade, later. Looked into taking the old plastic blocks completely off and making some new ones from thin glass/epoxy sheets (I've got the material) to replace them. But that would have pushed the output bank into the main chassis, using these replacements. A head scratcher.
Send me an email. I don't know how to attach pictures here.
Flick23@charter.net
The threads on the thumbs are upset at the ends, so that they are self retaining. What I did was to unscrew them (top row first-of course), first by hand and then with a pair of needle nose. Then, I tightened the nuts against the lock washers of the new units and took the small jamb-nuts off.
Start from the bottom row and thread on the new units. Torque them down (not too much) with the pliers.
I didn't strip the female threads of either of my POA-1500s (16 places). So you shouldn't have a problem.
I am planning a better upgrade, later. Looked into taking the old plastic blocks completely off and making some new ones from thin glass/epoxy sheets (I've got the material) to replace them. But that would have pushed the output bank into the main chassis, using these replacements. A head scratcher.
Send me an email. I don't know how to attach pictures here.
Flick23@charter.net
rickflaherty
New Member
Hi CJ,
I wish I had an owner's manual for these things. Then, I migt be able to figure out what hey're doing.
I have one for the left channel and one for the right. both are driving a pair of DQ-12s (one on each side had the woofer removed for refurb). When on high power settings, they will both cycle power at the same time, or close to each other. There's no specific timing to it, so it must have something to do with the signal they're getting. Both have thermally controlled cooling fans that hadn't come on the last time I had the experience.
What do you think might be happening?
Rick
I wish I had an owner's manual for these things. Then, I migt be able to figure out what hey're doing.
I have one for the left channel and one for the right. both are driving a pair of DQ-12s (one on each side had the woofer removed for refurb). When on high power settings, they will both cycle power at the same time, or close to each other. There's no specific timing to it, so it must have something to do with the signal they're getting. Both have thermally controlled cooling fans that hadn't come on the last time I had the experience.
What do you think might be happening?
Rick
markallen
Luddite Tendencies
Got a POA-1500 in mint condition for a song - but the lamps didn't work. Found this thread, ended up ordering the retrofit "premature lamp failure avoidance kit" of lamps, transistors and resistors from dgwojo. They arrived FAST - thanks!
Please note that the 2 transistors and 2 resistors to be changed are the first four components (from L to R) on the top edge of the PC board behind the face panel. It's probably best to remove this board, but it has a LOT of connectors, there are many obstacles, and a ground wire that would need to be de-soldered. I didn't do this, but did loosen it enough to pull the board up a bit. I placed the amp on its face on a clean soft terry towel folded several times. This allowed reasonable access to the solder side of this board. After that, it went easily, once I established that the 2SC1815 and the 2SC2655 have the same pinout pattern.
One other related item: The DENON lighted logo bulb was burned out also, but I'd ordered an extra 60 mV bulb from dgwojo. As the logo lamp is not on the same modified circuit as the meter lamps, when I pulled the indicator module (contains the DENON logo lamp, thermal lamp, L & R channel test lamps), I removed the existing 40mV lamp from the thermal indicator and installed one of the 60mV lamps there. I then reinstalled the old 40mV lamp in the DENON logo. As the thermal lamp only lights up for a couple of seconds on start up, I figured it really wouldn't put undue stress on that circuit. If anyone can fault this logic, please let me know!
I'll add that lately there has been an auction seller who is offering the actual NOS Denon lamp failure retrofit kit for this amp. Though he has a "make offer" option, don't waste your time; the best he'd do was to knock off 95 cents, saying "these kits are selling at my asking price so I don't really need to discount". Just as well, as I saved over $12 by ordering from dgwojo. AK delivers the right information again!
Please note that the 2 transistors and 2 resistors to be changed are the first four components (from L to R) on the top edge of the PC board behind the face panel. It's probably best to remove this board, but it has a LOT of connectors, there are many obstacles, and a ground wire that would need to be de-soldered. I didn't do this, but did loosen it enough to pull the board up a bit. I placed the amp on its face on a clean soft terry towel folded several times. This allowed reasonable access to the solder side of this board. After that, it went easily, once I established that the 2SC1815 and the 2SC2655 have the same pinout pattern.
One other related item: The DENON lighted logo bulb was burned out also, but I'd ordered an extra 60 mV bulb from dgwojo. As the logo lamp is not on the same modified circuit as the meter lamps, when I pulled the indicator module (contains the DENON logo lamp, thermal lamp, L & R channel test lamps), I removed the existing 40mV lamp from the thermal indicator and installed one of the 60mV lamps there. I then reinstalled the old 40mV lamp in the DENON logo. As the thermal lamp only lights up for a couple of seconds on start up, I figured it really wouldn't put undue stress on that circuit. If anyone can fault this logic, please let me know!
I'll add that lately there has been an auction seller who is offering the actual NOS Denon lamp failure retrofit kit for this amp. Though he has a "make offer" option, don't waste your time; the best he'd do was to knock off 95 cents, saying "these kits are selling at my asking price so I don't really need to discount". Just as well, as I saved over $12 by ordering from dgwojo. AK delivers the right information again!
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