Yamaha DSP-A3090 broken - Page 1
Forum section: electronics / repair

author: abhi1981
author_rank: Regular Contributor
timestamp: April 25, 2025, 11:45:47 am
content: HelloJust got a pretty beat up Yamaha DSP-A3090 for around $140. I picked it up mainly for the AC3 input for my LD player. The good ones usually sell upwards of $300. It is working, but when I opened it, I found that the entire video card containing the s-video connectors and monitor out is missing. Only the RCA jacks were there on the backplate. Looks like the amp had been dropped and the card broke due to the impact. But the AHwho fixed it removed the video card along with the front amp card and the rec selector switch and the entire wiring. To make the front channels work, he just jumpered them with the main spk out. Again what an AH. There was absolutely no reason to remove the front amp board as it is a separate board. And he even put a fake potentiometer to fix the rec knob.Now, I don't want s-video, but I would definitely like the front LR channels to work, although they are actually the front effects channel. Also, the monitor out should be there for viewing the settings on screen.Will it be possible to make a front amp circuit board and also tap the monitor out from the remaining circuit. Please help.I also have a Yamaha HTR 3063, which can be used for parts, if any.

author: abhi1981
author_rank: Regular Contributor
timestamp: April 28, 2025, 09:02:50 am
content: What is this the purpose of this modification? Please help.Connector #7 - DAR is shorted to FR with a 82ohm resistor.Capacitor C34 has been removed and and the positive legs of C34 and C38 has been shorted with a red wire.

author: m k
author_rank: Super Contributor
timestamp: May 01, 2025, 12:56:34 pm
content: Removing C34 means that this R is disconnected from its source.Shorting to C38 means that this R is rerouted in from somewhere else.Added resistor can mean that all functionality of DAR to FR is bypassed, compared to what DAL has before it becomes FL.If D means digital and FR is analog then this resistor can be a simple snubber/terminator for DAR.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 01, 2025, 04:16:23 pm
content: I have removed the resistor, installed a new capacitor and removed the jumper wire. The amp seems to be working fine.Even with the front channel amp removed, the preamp output should work.But, there is no output from the preamp sockets. The rear channel preamp is working.I will test the circuit continuity and will post further developments.I have also attached the full circuit diagrams.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 01, 2025, 05:48:50 pm
content: IC7 is missing(rather pulled out)No wonder there is no front output. But why was it pulled out???I wonder what else is missing from this poor old amp.IC7 was NJM2068MD, which is not available.Will LM4562 be the correct replacement? Please advise.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 01, 2025, 06:06:58 pm
content: Can I use NE5532 ?It has better availability.

author: madires
author_rank: Super Contributor
timestamp: May 01, 2025, 06:26:08 pm
content: The LM4562 would be the better choice, but NE5532 should be fine too.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 01, 2025, 06:43:45 pm
content: Thanks.Will get one and then we'll see how deep the rabbit hole goes.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 01, 2025, 10:50:32 pm
content: Can I use NJM4565M from my HTR3063?

author: madires
author_rank: Super Contributor
timestamp: May 02, 2025, 07:14:03 am
content: NJM4565M should work too, but isn't as good as the NE5532.

author: Haenk
author_rank: Super Contributor
timestamp: May 02, 2025, 07:31:29 am
content: Looks like you were scammed pretty badly - likely you were sold a parted out machine at a lower-than-usual price.I have doubts it will be up to the task with some major parts missing.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 02, 2025, 10:16:37 am
content: Yeah, it was a scam, but considering the riciculous prices good amps, this one was a steal. But fortunately all the channels, except the front effects channel, are working. I checked with optical input.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 02, 2025, 12:35:37 pm
content: Just put in the NJM4565 but no sound. There is a humming sound from the speakers when I touch the IC pins. Maybe the salvaged IC is fried or the DSP circuit is bad.

author: madires
author_rank: Super Contributor
timestamp: May 02, 2025, 01:12:44 pm
content: If you got a function/signal generator you could inject a 1 kHz sine wave into to the different stages to check which one causes the issue. The mains hum when touching the OPamp's pins is an indication that the stages after IC7 are likely ok.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 02, 2025, 08:33:20 pm
content: The dac chip is missing. Its an AK4320VM.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 03, 2025, 07:44:15 am
content: PCM5102 was suggested as a suitable alternative to AK4320.Please advise.

author: madires
author_rank: Super Contributor
timestamp: May 03, 2025, 02:04:54 pm
content: I think it's time to learn reading datasheets.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 03, 2025, 04:30:09 pm
content: If I could read datasheets, then I probably wouldn't need your help

author: abhi1981
author_rank: Regular Contributor
timestamp: May 08, 2025, 03:28:40 pm
content: Last but not the least, THE HEADPHONE AMP IS MISSING TOO!!!!!!!I have assembled back everything, but now there is no output. The optical and analog inputs are not working.Earlier it was working beautifully on 5.1 channel and optical was working too.Except the Main LR, all the remaining channels are producing a test tone in test mode.I had opened the volume control for cleaning, but it is working in test mode.As I'm using the remote to change inputs, I have left the input selector disconnected (I'm trying to fix a broken gear). Could that be the reason?Or maybe its a ribbon cable.Please help me diagnose the issue. I don't know where to start.

author: madires
author_rank: Super Contributor
timestamp: May 08, 2025, 06:30:55 pm
content: Yes, if the input selector is a rotary switch.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 08, 2025, 07:12:44 pm
content: Yes, it is a motorised rotary switch.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 09, 2025, 10:57:04 am
content: Quote from: madires on May 08, 2025, 06:30:55 pmYes, you are right. Putting it back solved the input problem. Even after cleaning, it is still a bit dodgy.But the volume is very very low. At full volume it is barely noticeable. I touched the bass treble board and there was a loud hum. It has some damaged traces and repairing has been done with jumper wires. I'll check it again for more damaged traces.

author: madires
author_rank: Super Contributor
timestamp: May 09, 2025, 01:54:49 pm
content: Several of the old Yamaha amplifiers use ALPS rotary switches as input selector and they are known to become flaky after a while. For whatever reason the engineers chose a switch type without gold plating which is problematic for line level audio signals. It's possible to take the switch apart, and clean and lubricate the contacts. But it will only last for a few years and the switch will become flaky again.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 09, 2025, 02:06:20 pm
content: I have cleaned the contacts. I really want the motor function to work, but I could'nt find a replacement gear.

author: madires
author_rank: Super Contributor
timestamp: May 09, 2025, 05:08:52 pm
content: Another thing to check is if your amp has a super cap for the settings RAM. If it lost too much capacitance or leaks it needs to be replaced.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 09, 2025, 05:30:00 pm
content: Indeed it does have a super capacitor. But I'm beginning to think that the modifications, which I have mentioned earlier, have been done for this no sound problem.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 09, 2025, 06:29:55 pm
content: I restored the modifications and its working again.Any idea as to what those modications are??

author: madires
author_rank: Super Contributor
timestamp: May 10, 2025, 08:30:39 am
content: Looks like DAR is fed into FR, the signal path for DAR is interrupted after the volume pot (C34 missing), and then FR is bridged to DAR again. A bypass for a bad volume pot (multigang)?

author: abhi1981
author_rank: Regular Contributor
timestamp: May 10, 2025, 08:40:02 am
content: Thanks Madires. Yes, its a motorised multigang pot.Please see Pg 61 and 62 of the service manual which I have uploaded earlier.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 10, 2025, 09:27:29 am
content: Checked the preamp outputs, with 5.1 optical input.Very low volume in main R and no volume in rear L. Rest of the channels are ok.

author: madires
author_rank: Super Contributor
timestamp: May 10, 2025, 12:37:36 pm
content: One picture you've posted ealier shows the power transistors missing for one channel. Do you know which channel? The missing OPamp IC7 is for FL and FR. And which channel is the missing DAC IC27 for? Maybe there's a pattern.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 10, 2025, 12:48:42 pm
content: IC27 is also for FL and FR. Everything related to front channel has been removed.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 10, 2025, 07:42:47 pm
content: Quote from: abhi1981 on May 10, 2025, 09:27:29 amSorry, its the other way around. Very low volume in main L and no volume in rear R

author: abhi1981
author_rank: Regular Contributor
timestamp: May 12, 2025, 06:52:47 am
content: The vol pot does have a bad track, which is Main R.My guess is that someone might have tried to rotate the knob full 360 deg, like modern digital ones, and broke the stop tab. This twisted tab of metal scraped off the carbon track so much that it severed the connection. I tried to solder what seemed like brass, but it wasn't. The solder didn't stick to it.Anyways, after modifications, I managed to fit the track of another 100k pot.It pot is working now, but there is still very low volume from the main left channel. I have removed the earlier cap/res mods.Earlier, when I touched the bad pot pins, there was a loud humming from the speakers which has gone now.But, the same is there when i touch the mica caps on the bass treble control board.The main amp is ok. I checked the preamp inputs.

author: madires
author_rank: Super Contributor
timestamp: May 12, 2025, 08:56:06 am
content: Nice job with the pot! To make sure the low volume on main left isn't a setting have you reset the amp?

author: abhi1981
author_rank: Regular Contributor
timestamp: May 12, 2025, 09:22:00 am
content: Thanks. Luckily the donor pot was the same fake one that I mentioned earlier. I had to drill a hole and chip off the edges. It was a perfect fit.Just found a rotten trace that carries the main L signal to the bass extension switch. That might be the cause. There are several bad traces on that particular board. I'll check them all.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 12, 2025, 10:36:24 am
content: Repairing the trace greatly improved the level, but still it is 50% lower then the R channel. I will try factory reset.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 12, 2025, 11:03:38 am
content: Nope, factory reset didn't help.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 13, 2025, 06:49:07 am
content: How do I do signal tracing with an oscilloscope? I have a TEK2235.Do I need dummy loads?

author: madires
author_rank: Super Contributor
timestamp: May 13, 2025, 07:25:30 am
content: Take a signal source, e.g. 1 kHz sine, inject the signal und use the scope to follow the signal. A dummy load is only needed for measuring output power and some other things, but not for signal tracing.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 13, 2025, 10:01:21 am
content: The L vol pot seems to be defective.That means the R pot, that was damaged, was actually ok. The L was defective all alongI will have to repair it againThis image shows the comparison between L and R output signals from the pot.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 13, 2025, 10:04:26 am
content: The LR input signals to the pots.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 13, 2025, 10:08:45 am
content: I used a 1k hz youtube video as an input signal

author: madires
author_rank: Super Contributor
timestamp: May 13, 2025, 10:16:39 am
content: A PC's audio output is fine too and you can get audio test software for free.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 13, 2025, 04:19:03 pm
content: The Yamaha part no. for the pot is VT882400 Y100K.What is Y type pot???I used a W100K for repair.I cannot find much info about W or Y type.Only A and B seem to be available.

author: madires
author_rank: Super Contributor
timestamp: May 13, 2025, 05:06:51 pm
content: Y is negative logarithmic, W is negative logarithmic up to the midpoint and positive logarithmic beyond.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 13, 2025, 06:23:17 pm
content: Both L and R pots are showing almost identical increments, on a multimeter, while the pot knob is turned.Upto 50% - the resistance drops gradually to about 85ohms, then rapidly to 0hms. That means the pot is ok.What else could be the problem??

author: madires
author_rank: Super Contributor
timestamp: May 13, 2025, 06:45:09 pm
content: The next step would be to check the L/R stages after the pot (signal before and after each stage).

author: abhi1981
author_rank: Regular Contributor
timestamp: May 13, 2025, 07:20:18 pm
content: I already checked that. The cro readings are taken directly from the pot legs. Both LR signals are identical while entering the pot, and while exiting, the L signal is weaker than the R signal.

author: madires
author_rank: Super Contributor
timestamp: May 13, 2025, 07:48:38 pm
content: If the pot is fine that would mean that something is loading down the L signal. IIRC, after the pot there's a 1 MOhm resistor to ground and a 2.2 µF coupling cap for the OPamp stage. Do have both channels the coupling cap installed? Or is one missing the cap?

author: abhi1981
author_rank: Regular Contributor
timestamp: May 13, 2025, 08:12:36 pm
content: You are right. C34 was missing (the mod which I mentioned earlier). I replaced it with a same value cap ( jamicon tl series- don't know if its original) Could that cap be the culprit?

author: abhi1981
author_rank: Regular Contributor
timestamp: May 13, 2025, 08:28:55 pm
content: I measured the resistor and caps and values are as below -R85 56k and C33 300k nearly stableR87 rising to app. 900k and C34 falling quickly from 2M toapp. 1M

author: abhi1981
author_rank: Regular Contributor
timestamp: May 13, 2025, 09:29:54 pm
content: There is definitely something fishy about these jamicon capsI tested their resistances and two of them started from 20M and went upto over 90M and beyond, and another two started from 40M and dropped to 10M and below. They might be fake.

author: madires
author_rank: Super Contributor
timestamp: May 14, 2025, 06:48:56 am
content: R85 and R87 are in parallel with the pot's bottom halfs. And at the input and output of that stage there are coupling caps. If the pot's tapers are the same both channels (R85 and R87 ) should measure also about the same. You could remove the two coupling caps C33 and C34 and check the signal levels again to verify if the pot/1MOhm stage for L is fine.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 14, 2025, 08:49:53 am
content: I removed C33 and C34 and now the amplitudes of both are almost same upto about 50% of the turn. After 50% , R stops increasing and L continues to rise normally.

author: madires
author_rank: Super Contributor
timestamp: May 14, 2025, 10:24:38 am
content: We should keep that in mind, could be another issue. Anyway, let's continue with the IC5 OPamp stage for channel L. Start with replacing C33 and C34 with new caps (or whatever you've got in the drawer) and check the signal levels again. If L is low in comparison to R that would point to the OPamp stage.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 14, 2025, 07:11:37 pm
content: Changed both caps - no change. Attached pic shows amplitude at 50% turn. Ch1 is R and Ch2 is L.

author: madires
author_rank: Super Contributor
timestamp: May 14, 2025, 07:43:53 pm
content: The circuit diagram notes a +16.5 dB amplification for the IC5 OPamp stage. That would be a factor of 4.5. Does that match with the signal levels after the OPamp stage?

author: abhi1981
author_rank: Regular Contributor
timestamp: May 14, 2025, 08:08:52 pm
content: I don't understand factor of 4.5.I measured IC5 voltagepin8 +14.3vpin4 -13.97v

author: madires
author_rank: Super Contributor
timestamp: May 15, 2025, 07:07:14 am
content: The audio signal should be amplified by a factor of 4.5. When you compare the signal going into the non-inverting input of the OPamp with the signal at the OPamp's output its voltage should become 4.5 times higher.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 15, 2025, 07:42:46 am
content: R is amplified 5 times and L only 3 times at the OPamp's output.

author: madires
author_rank: Super Contributor
timestamp: May 15, 2025, 09:48:56 am
content: So something is wrong with that L channel OPamp stage. The next step is to check the passive components of that stage (R86, R101, C42, R102 and C41). My bet would be on C41 (lost capacitance). Since IC5 is amplifying it's unlikely to be bad.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 15, 2025, 11:24:32 am
content: Changed C41 and C44. No change in output.R channel seems a bit too loud.

author: madires
author_rank: Super Contributor
timestamp: May 15, 2025, 12:20:16 pm
content: Are the other passive components ok?

author: abhi1981
author_rank: Regular Contributor
timestamp: May 15, 2025, 02:13:20 pm
content: Yes, the others are ok.Could be something else down the line. If the line ahead IC5 is disconnected somehow, and if the signal is ok, then IC5 will not be at fault.

author: madires
author_rank: Super Contributor
timestamp: May 15, 2025, 04:58:25 pm
content: The issue should be around the volume pot or IC5 because the 1 kHz sine has the same amplitude for L and R before the volume pot.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 17, 2025, 07:05:14 pm
content: I think I found the problem. Its the volume pot that I changed. The original pot has 1KΩ and 20KΩ resistance at 90° and 180° turns respectively. Whereas, the replacement one has 10KΩ and 60KΩ resistance at 90° and 180° turns respectively. That's why the R channel was so loud.Now I will have to look for a A100K dual pot and replace both the original tracks, so that the tracking is equal on both channels.Right now the market is flooded with B100K pots. A dual type A pot will be difficult to get.I tried repairing the old one by rubbing a pencil over the cracked trace. Its working, but its adding an additional 4-5KΩ. Conductive paint might do the trick, but its damn expensive.

author: m k
author_rank: Super Contributor
timestamp: May 21, 2025, 05:42:05 pm
content: Forget the paint, it's too fragile.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 21, 2025, 06:10:23 pm
content: I don't have many options.If paint doesn't work, then since A type pot is not available, then I will have to convert B pot to log by resistor mod.Paint might work because the crack is not in the path of the wiper..

author: m k
author_rank: Super Contributor
timestamp: May 23, 2025, 11:18:54 am
content: Amazon has many pots, maybe too many.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 23, 2025, 11:29:29 am
content: Amazon India has got only B type pots. I even ordered from one seller, who was selling both A and B pots, but I received both B type pots. I was not surprised and even the seller doesn't know the difference between them. Here they will sell whatever they have.Anyways, tried the paint today. The paint has good conductance, but, as you said, it is a bit fragile.What if I seal it with green UV glue?

author: m k
author_rank: Super Contributor
timestamp: May 23, 2025, 07:47:30 pm
content: Better try AliExpress or near by electrical music instrument store.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 23, 2025, 08:10:40 pm
content: The main problem is that Aliexpress is banned in India.And local shops and online shops are all selling B type pots, saying they are all the sameThose shops that actually have the stuff are wholesellers, and will not even talk to small retail customers.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 25, 2025, 07:01:47 pm
content: It's fixed!!!!!It was the volume pot. The R vol trace measurement was off by 10K after the repair, so I switched it with the LFE one. The 10K difference wouldn't matter as the LFE is a single channel and it uses a powered sub, which of course has it's own volume control.The amp is working beautifully now.I changed the pot body with the B100K one, since I was afraid the tabs on the older one might break, as it was already opened 2-3 times.Thanks, everyone, for your invaluable help! I couldn’t have figured this out without your insights, and I truly appreciate the time and effort you put into guiding me.The only thing left is the front channel and video out, which will be a future project.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 25, 2025, 07:07:26 pm
content: Also, I didn't bend the tabs of the motor unit. I just put a glob of solder on them, so that they can be easily removed after desoldering.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 31, 2025, 09:44:03 am
content: More missing components.Just when I thought that it was over.Q1, Q2, Q3 and Q4 all missing. In the schematic it says audio trim. What's that?They have something to do with analog input.

author: madires
author_rank: Super Contributor
timestamp: May 31, 2025, 10:50:03 am
content: It's a switchable attenuator. The first transistor pair enables a -4dB attenuator for L and R, and the second pair a -2dB attenuator.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 31, 2025, 11:39:27 am
content: What is an attenuator?How will the missing transistors affect the analog input?Also, 2SD1915 is not available. Please suggest a suitable substitute.

author: madires
author_rank: Super Contributor
timestamp: May 31, 2025, 12:52:36 pm
content: An attenuator reduces the signal amplitude, like a volume pot. The BJTs are switching the two attenuators, i.e. without them the attenuators can't be enabled. The signal will simply pass that stage without attenuation. Any jelly bean NPN (hFE > 500) should do the job.

author: abhi1981
author_rank: Regular Contributor
timestamp: May 31, 2025, 01:32:23 pm
content: That means the audio will be louder without attenuation. He must have removed them to increase the volume.

author: madires
author_rank: Super Contributor
timestamp: May 31, 2025, 03:16:09 pm
content: Let's check the circuit diagram. The control lines of both attenuators are interconnected, acting as one -6dB attenuator. And they seem to be enabled via a simple 5V Zener based voltage regulator fed by the +15V rail. Those 5V also power the LC7536s (electronic attenuator). Should be part of the operation mode control.

author: abhi1981
author_rank: Regular Contributor
timestamp: June 06, 2025, 03:28:41 pm
content: I used four 2SC1815Ys, that I had in stock. Didn't notice any difference.Some analog inputs like CD and TUNER are not working. TAPE PB is working, even with the input selector switch on a different input. Maybe it has something to do with the missing REC SEL. switch.I have ordered a similar 1 pole 12 position switch and the resistors. That should fix the rec out selector.

author: abhi1981
author_rank: Regular Contributor
timestamp: June 21, 2025, 07:39:35 am
content: Fixed the REC.SEL. switch. The analog inputs are working now, but its still acting funny.By rotating the rec sel, the volume of the inputs is also changing. Also, the output of a particular input is available on all the other inputs.I also changed the supercapacitor, now the last input memory is being retained. Earlier the input selector switch rotated to the top position every time the amp was turned on.Got the broken gear of the input selector 3d printed. Its working now.

author: abhi1981
author_rank: Regular Contributor
timestamp: June 21, 2025, 08:05:07 am
content: This is how it looks like now.The volume control knob is not original. I made it from a 40mm PVC end cap and coloring it black with permanent marker ink and acetone. Not perfect, a bit out of round, but it does the job.The door hinge was broken too. All fixed now.