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Denon PRA-1100 & POA-2200

PTL-Pioneer

Super Member
Hi all
Bought first bits of denon there recently, power amp needs work because speaker terminals all smashed up, the plastic is super brittle. Seems like really nice build quality other than those terminals obviously. Ill post more on that when i take a look at it properly.

The preamp needed a serious cleanup, and I Recapped everything on it, using film caps anywhere I could, there are a lot of 1uf caps in this unit. I used upw series nichicon everywhere except the phono section, I tried to keep it to ukl series there.
Build quality is very nice indeed.
Listening to it now connected into my onkyo a10, really nice, seems very neutral.

I seen lots of questions around opamps upgrades etc, but cannot see why it is needed, Denon seemed to have done a great job.

What I a struggling with just a little is how to setup the preamp per the service manual. I cannot see the test points I am supposed to clip onto to dial everything in.
Is it just one side of the volume pot from each channel?

upload_2021-10-10_18-6-7.png
 
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Same, less than useful, diagram for my PRA 1200. You just have to estimate by the shape of the circuit printing and number of pins over. You will get a reading close to what you are expecting, adjust that side to make sure you have the correct pin. Plan B is to trace the circuit to the main board.

I second your observation on build quality. Not a Yamaha but close.
 
yes it is certainly less than useful for sure, especially for idiots like myself who cannot read a schematic properly.

I had the PRA1100 connected to an onkyo a10 currently running to Qacoustic concept 20 speakers and it sounds good, but any songs that have heavy bass make the bass sound a little tinny in the speakers.
Might be a synergy thing, but its actually weird

All music sounds great but when the bass hits heavy the PRA1100 makes those low bass notes sound poor on the speakers.
Tonight ill try the jamo c103 and see does a different set of speakers produce the same result
 
I found out the cause of the weak/weird/sloppy bass. I didn't solder one leg of a film cap, I'm surprised it played at all!


All fixed now, I'm super impressed with the preamp, really really clean sounding.
 
DSC_0084.JPG


Moving to the poa-2200 now.
Speaker terminals are smashed up badly in one side, going to have to replace all of that. Tested with some alligator clips, I have sound in both channels, great, everything needs a clean and a deoxit treatment.

Will recap the amp next, I want to avoid touching any transistors or diodes but I would really appreciate any guidance you all have on this, I cannot see any of the shoot on sight transistors in this unit.
 
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Hi all, got this unit all recapped throughout, kept the filter caps and existing relays.

Powered up on dbt safely to test and have distortion in the right channel. I thought when i initially tested this unit that it was just dirty pots, unfortunately it looks like i may have some hurt transistors??

I can set bias on the left channel nicely, but the right channel does not move at all when i adjust the pot so i left it be.

I bought this unit as spares/repair thinking it were just the speaker terminals that were busted, obviously some other hidden issues to be found.
At a bit of a loss as to where best to look next, my toolkit is DBT, multimeter and cheap component tester.
The component tester is only good for identifying parts, it wont tell me if a transistor is hurt, only if its shorted.

I would appreciate some help from some of the gurus as to where best to start i can post voltages etc

Service manual detailed below (if link not allowed let me know and i will remove it immediately)

https://www.hifiengine.com/manual_library/denon/poa-2200.shtml


DSC_0178.JPG DSC_0177.JPG DSC_0176.JPG
 
For review for potential replacement, work in progress for me, still some more digging to do.
Cheekily calling on @merlynski for some guidance

Picture i found on the internet - this is not mine i did not generate it and can remove it if it infringes on anybody
denon poa2200 schematic stages colored.JPG

2sc3298 = ksc2690ays
upload_2021-10-27_9-16-33.png

2sa1306 = ksa1220ays
upload_2021-10-27_10-19-45.png

2sc2238 = MJE15032

2sc2705 = ksc2383yta
upload_2021-10-27_20-34-13.png


2sc3423 = ?
2sa1360 = ?
2sc3334 = ?
 

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I am going to buy some freezer spray to hopefully be able to identify the dodgy transistor, and i remember that i had a set of active speakers and a rca probe with film cap attached, that i could use to probe the circuit
 
Well damn it. Had unit on for a bit today to check voltages and something popped. It must have been just waiting to happen. Need to come back to it when head is clearer, today I have had enough.
 
Sorry to hear of the troubles yesterday. I’m not much above ascending amateur status at repairs like this, and I don’t have this actual unit (closest is a PMA-900V, which shares some design aspects in its amp section), but I can offer some advice on how to start evaluating the current situation.

You can (and should) do the following checks with the unit unplugged, and nothing connected:

— Check the fuses on board ETC9071-4 (same board as the bank of 8 large PS caps). There are 8 total, 4 x 8A and 4 x 5A. These are rail fuses, through which power is supplied to the output transistors, among other things. If any of these fuses are blown, it is likely some of the output transistors (the ones bolted to the large heat sinks) are shorted, or another short exists (e.g., from the recap).

— Check the continuity between the C and E (collector and emitter) leads on the 8 output transistors; there will be 4 mounted to the right heat sink, and 4 to the left heat sink. If the PCBs are like the 900V, they will be well marked, including not only the part number for the transistors, but also the pin labels for 2 of the 3 pins; from that you can determine the label for the missing one by elimination (C, E, and B are the only possibilities). This check for C-E shorts can be done in circuit; no need to desolder them. If any of them shows a short, it will need to be replaced.

— Check the resistance of the emitter resistors R634/R636 and R633/R635. From the schematic, it looks as though internally each of those is two 0.18Ω resistors with a third (center) lead between; if so, you can just measure off the end leads, and should read something consistent with 0.36Ω. Since these will be in circuit, alternative paths could lower the measured resistance, but that should be minimal. N.B.: some DMM are not good at measuring such low resistances. It isn’t a bad idea to, after making a measurement, follow it by noting the resistance you get when you just cross the DMM probe tips; the difference between these two measurements might be a better measure of the resistor’s value.

— If any of the transistors and/or resistors indicate damage, you want to check the transistors further upstream (the drivers, then the pre-drivers; just work to the left on the diagram in your post #8), and possibly other components. You can check for C-E shorts in the same way as above, but for a more complete check of them, you probably should consider desoldering them and checking them on your component tester (if it identifies C, E, and B, it does more than just identifying shorts, which could be done adequately in circuit). A general rule seems to be to replace the first of the transistors upstream from the last damaged one.

Lastly, I’ll say that from what you describe as your initial checking of the unit after recapping, where you had “distortion” in the right channel, if that distortion was something like weak and variable static, it would match what my experience was with a Denon 500V, which had blown rail fuses and shorted output transistors in one channel. But if the situation prior to the recap was not the same (you said you had sound in both channels), something probably went wrong during the recap, so check all of that work carefully, things like bridged solders, caps installed with improper polarity (the latter might have resulted in a popped cap).

I hope this helps, and I wish you better luck with the followup.
 
Sorry to hear of the troubles yesterday. I’m not much above ascending amateur status at repairs like this, and I don’t have this actual unit (closest is a PMA-900V, which shares some design aspects in its amp section), but I can offer some advice on how to start evaluating the current situation.

You can (and should) do the following checks with the unit unplugged, and nothing connected:

— Check the fuses on board ETC9071-4 (same board as the bank of 8 large PS caps). There are 8 total, 4 x 8A and 4 x 5A. These are rail fuses, through which power is supplied to the output transistors, among other things. If any of these fuses are blown, it is likely some of the output transistors (the ones bolted to the large heat sinks) are shorted, or another short exists (e.g., from the recap).

— Check the continuity between the C and E (collector and emitter) leads on the 8 output transistors; there will be 4 mounted to the right heat sink, and 4 to the left heat sink. If the PCBs are like the 900V, they will be well marked, including not only the part number for the transistors, but also the pin labels for 2 of the 3 pins; from that you can determine the label for the missing one by elimination (C, E, and B are the only possibilities). This check for C-E shorts can be done in circuit; no need to desolder them. If any of them shows a short, it will need to be replaced.

— Check the resistance of the emitter resistors R634/R636 and R633/R635. From the schematic, it looks as though internally each of those is two 0.18Ω resistors with a third (center) lead between; if so, you can just measure off the end leads, and should read something consistent with 0.36Ω. Since these will be in circuit, alternative paths could lower the measured resistance, but that should be minimal. N.B.: some DMM are not good at measuring such low resistances. It isn’t a bad idea to, after making a measurement, follow it by noting the resistance you get when you just cross the DMM probe tips; the difference between these two measurements might be a better measure of the resistor’s value.

— If any of the transistors and/or resistors indicate damage, you want to check the transistors further upstream (the drivers, then the pre-drivers; just work to the left on the diagram in your post #8), and possibly other components. You can check for C-E shorts in the same way as above, but for a more complete check of them, you probably should consider desoldering them and checking them on your component tester (if it identifies C, E, and B, it does more than just identifying shorts, which could be done adequately in circuit). A general rule seems to be to replace the first of the transistors upstream from the last damaged one.

Lastly, I’ll say that from what you describe as your initial checking of the unit after recapping, where you had “distortion” in the right channel, if that distortion was something like weak and variable static, it would match what my experience was with a Denon 500V, which had blown rail fuses and shorted output transistors in one channel. But if the situation prior to the recap was not the same (you said you had sound in both channels), something probably went wrong during the recap, so check all of that work carefully, things like bridged solders, caps installed with improper polarity (the latter might have resulted in a popped cap).

I hope this helps, and I wish you better luck with the followup.


Many thanks for your reply, grateful for all advice
I can see already that one of the fuses have popped. Ill check them properly with multi-meter tonight if i can.
And C588 has popped also, not holding out much hope for those output transistors to be honest.
New ones cannot be found easily either to make matters worse, and i was struggling to begin with in the selection of replacement transistors

The distortion never changed from initial testing to after recap testing, originally i presumed dirty pots.
The recap went fine as far as i can tell, this unit had been powered up for hours after i got the recap done, passed all DBT tests etc.
I do one cap at a time and i work off of pictures i take before i do anything, i also verified cap orientation using the opposite channel.

Either way this amp seems to be trying its hardest to break me!

What i will do
1. Pull all fuses and check
2. Remove emitter resistors R634/R636 and R633/R635 and ohm them
3. Remove the output transistors and test them with my cheap meter
4. Report back

Thanks for the guidance! The good folks here are probably running low on patience with me, always something wrong! :)
I am a slow learner thats for sure
 
3. Remove the output transistors and test them with my cheap meter

The output transistors have a lot of solder on them, making them some work to remove. I encourage you to test them for C-E shorts while in circuit. It is easy and the results can be telling.

As to selecting transistors, this amp isn't that old and I am sure suitable replacements for things at the back end of the amp are available (that can't always be said for FETs on the front end). In fact, I just checked bdent and they have your output transistor pairs (TR531-TR538, Sanken 2SC3519 and 2SA1386) in stock. And installing new outputs seems a lot less formidable once you've done one. After my recent experience with the PMA-500V (https://audiokarma.org/forums/index...placements-for-sanken-2sa1106-2sc2581.967679/), I feel I have enough of a sense to get you started on selection of other transistors if need be, and others here will chime in, but it might take a new post with specific transistors listed in the thread title to elicit comments, when that time comes. But first do the C-E short tests.

C588 sits between the +72V rail and ground on the right channel; it should see the same conditions as C587 on the left channel (they both root back to the same places in power supply). It would seem you either have other damage (transistors presumably) on the right channel, or you got unlucky with a faulty new cap for C588 when you recapped (recheck that it is a 100V cap).
 
Thanks Northpaw, i tried checking the outputs in situ but my meter doesn't read em properly so ill have to remove them i think in order to test.
My little tester does not read these either, it goes into a "Self test mode", first time i have seen that.

Using a multimeter on diode setting

NPN transistor 2SC3519A - TR532
Positive lead on the base. Negative lead on the emitter = 0v
Positive lead on the base. Negative lead on the collector = 0v
Negative lead on the base, positive on the emitter = 0V
Positive lead on the collector, negative to the emitter 0V
This one is dead

Using a multimeter on diode setting
NPN transistor 2SC3519A - TR534
Positive lead on the base. Negative lead on the emitter = 0.32v
Positive lead on the base. Negative lead on the collector = 0v
Negative lead on the base, positive on the emitter = 0.33V
Positive lead on the collector, negative to the emitter 0.34V
This one is dead also

further test to follow, need to pull the 2SA1386 next and test
 
For the simple in-circuit C-E short tests I mentioned, you use the resistance mode on the meter. It should be straightforward, unless the meter is malfunctioning. You can check it on the transistors you already pulled and tested bad via the diode test.

On the little component tester, if it is the one I am thinking, the small LCR-TC1 (I have one as well), they sometimes go into Self Test mode when connected to a badly damaged component, like a shorted output transistor. The fix to that is to disconnect the component, and then give the button a long press (> 1.5 sec). That should bring it back to life. It may do it again if connected to a similarly damaged component; if so, just repeat the above fix.

Yes, those measurements on the unmounted transistors indicate they are dead. Probably all 4 on the right channel are damaged, and should be replaced even if any seem to test ok. You should also determine what rail fuse(s) are out, and do they align with the rail(s) that each failed transistor is on, as this will confirm cause and effect. If that is so, it seems likely that there was a catastrophic, user-induced event in this amp's history, such as shorted speaker wires on the right channel.

Hopefully this will turn out like my 500V, and replacement of the outputs and the adjacent set of driver transistors (even though they were not shorted) will correct the problem.
 
Yes amp came to me as non working, speaker terminals on right side had been smashed up badly, I need to replace them as part of this restoration, which is now a repair.

Thanks for taking the time to help me with this, I'll have more details tmro
 
Here is a thread on AK by sinnerboy describing a clever way retrofitting new speaker wire binding posts to the existing rear inset panels. His method did minimal alteration to the inside, not even requiring touching the PCB itself. Looks very neat and factory-like on the outside, and you end up with a better quality connector. Many seem to dislike the bare-wire-only connector Denon used on some of their high-power integrated and power amps during this period (my PMA-900V has them). I don't mind them so much, but their quality really isn't the highest, especially considering what these units cost back then.

https://audiokarma.org/forums/index...post-upgrade-path-of-least-resistance.934123/
 
Thanks for that, i am doing something very much like that, i have ordered some black anodised aluminium sheeting and some decent binding posts with isolation hardware. I'll be able to mount everything nicely and keep it all looking good all going well. I'll make sure that I show all that in this thread. Remember when unit came to me the rear right channel speaker terminal block was all smashed up, I think if you look closely at the first dusty image of the amp it can be seen

Struggling to get the time to work on this today, life gets in way of hobbies!

Quick checking ohming out E and C of the other two output transistors shows them to be OK, but I'll verify them properly same as above

I actually have restored a few amps at this stage, an onkyo a7090, a10 and a few pioneers too with the help of the great people on audiokarma. I struggle when things go wrong as I cannot read a schematic and missing the electronics knowledge.

Thanks for the help
 
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Updates:

It was F6 fuse that blew

TR536
PNP transistor 2SA1386A - TR532
Positive lead on the emitter. Negative lead on the base = 0v
Positive lead on the collector . Negative lead on the base = 0v
Negative lead on the emitter , positive on the base = 0V
Positive lead on the emitter, negative to the collector = 0V
This one is dead

Using a multimeter on diode setting
PNP transistor 2SA1386A - - TR534
Positive lead on the emitter. Negative lead on the base = 0v
Positive lead on the collector . Negative lead on the base = 0v
Negative lead on the emitter , positive on the base = 0V
Positive lead on the emitter, negative to the collector = 0V
This one is dead

Will pull some more transistors tmro and report back, thanks
 
Assuming these PNP are TR536 and TR538 (I see the TR536 but the 532/534 labels in bold seem to be typos, left over from before), yes, it seems all 4 outputs on the right channel are blown.

You say F6 blew. That feeds the +72V rail, for right channel only, and that goes with TR532/TR534 being blown. Did you determine if there is a short between C and E on these two transistors, by ohming between those two pins? I would think that they probably are shorted, and verifying that might explain the difference between what you are finding on the +72V and -72V rails (see below).

Since you did not mention it, I assume you found F8 to be intact. F8 feeds the -72V rail, for right channel only, and TR536/TR538 are on that rail. TR536/TR538 are blown according to your measurements, but you ohmed between C and E pins (post #18) you did not measure a short. That TR536/TR538 have failed but not shorted C-E could explain why F8 did not blow (TBH, I am not familiar with possible multiple failure modes for these transistors, such being dead but not shorted). But you can assume the -72V rail was stressed during the failure event, and I would replace F8 even if it checks out OK.

As we were discussing before, you want to go one step upstream in the circuit (this would be to TR528 and TR530**) to check for damage (also look carefully at other nearby components for any evidence of heat stress). Testing with the component tester would be best for this (although skip that if you ohm them C-E and they are shorted, as that will cause the component tester to go into self test mode again). Even if these transistors test good, you should consider replacing them anyway, and then you should be done with transistor replacements. If they are indeed damaged, replace them but also then go one further step upstream (TR524 and TR526), and repeat testing. The principle is to replace one step upstream from the last observed damage.

I have somewhere in my "notes to self" that you can get some idea if upstream damage has occurred by measuring for B-E and B-C shorts on those damaged TR532/534/536/538 transistors. If they are not shorted, it is likely there isn't damage upstream. These transistors are already removed and are easy to test for shorts, but if needed, the remaining transistors that are not yet removed can be tested for B-E and B-C shorts in circuit as well by ohming their leads.

** Looking at your first photo in post #7, I see that TR528 and TR530 are heat sinked, and that TR530 has an extra nut on its tab, and two crossed black wires immediately in front of its face. I'm not positive what these are, but I think they are a sensing component (a thermal tracking diode) stuck in the hole in the tab (or near it, since the bolt is present). I first saw this in my PMA-900V, which shares a lot of circuitry with the POA-2200 (see this thread on the PMA-900V, which contains a lot of potentially useful info for you -including transistor subs- since the amp circuits are so similar, but the discussion of the tracking diode starts in post #25, and post #33 has a good photo of the diode stuck in the hole; the driver transistor in the 900V is not bolted to a heat sink, so the mounting of the tracking diode is likely to be somewhat different than what you will find in the 2200. https://audiokarma.org/forums/index.php?threads/denon-pma-900v-troubleshooting.944587/). The equivalent sensing diode on the right channel of the POA-2200 is D528, and despite the fact that it is physically placed with TR530 (no electrical connection), it is located on the schematic in a location quite remote from TR530 (you can find it just to the left of TR522, the bias transistor). I mention this because you will likely need to pull TR530, so you have to be careful about separating that diode from the transistor (again, there is no electrical connection to TR530), and replacing it in the same position as you found it when you reinstall. There will be some heatsink compound slathered on it, and you should duplicate that when you replace. My understanding of the purpose of this sensing diode is to modify the amp's bias if TR530 starts to overheat.

Lastly, given the smashed right channel speaker terminals and the transistor damage you are now finding, it seems possible to imagine the failure event. The amp might have fallen, or had something fall onto it, while powered, and the physical damage to the right channel speaker connectors caused the right + and - wires to be shorted, leading to the electrical damage you are finding. Equally possible is the physical damage occurred while powered off, such as if the amp was dropped while carrying it, but the previous owner did not heed that damage and powered the unit on, and it was electrically damaged then.
 
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