Sony STR-DN1030 Distorted audio when Volume adjusted

[R_J]

Re: Sony STR-DN1030 Distorted audio when Volume adjusted

If R709 was open, you need to look at how it would open, Q703 would short C~B so +59 volts was likely on the base. so I would check and compare the values of R707,706,708 and Q701,702, if they seem to be ok, the next path is through ic701

[jason123]

Re: Sony STR-DN1030 Distorted audio when Volume adjusted

Actually... I think you're on to something. The datasheet for the MP1620 is cryptic, but it sure shows i got the wrong part. The MP1620 should have been -Y, but i seem to have gotten -P installed... -Y is on order. Hope that does it. I will keep you updated. Thank you!

[CapLeaker]

Re: Sony STR-DN1030 Distorted audio when Volume adjusted

Yep, it's a dumb mistake that can very easily happen as not always folks are aware about the gain value (hfe).
When I source replacement transistors with something else than stock, in one case I bought 25 pieces and matched a pair to the original spec on the working channel, then made another matched pair and exchanged the other channel too. I think the transistors also had to be backwards mounted, since the leg configuration was opposite, but that didn't matter, since there was no heat sink involved.
So when you did the transistor pair (NPN and PNP), where they both having different gains, or just one transistor?

[jason123]

Re: Sony STR-DN1030 Distorted audio when Volume adjusted

Yep, it's a dumb mistake that can very easily happen as not always folks are aware about the gain value (hfe).
When I source replacement transistors with something else than stock, in one case I bought 25 pieces and matched a pair to the original spec on the working channel, then made another matched pair and exchanged the other channel too. I think the transistors also had to be backwards mounted, since the leg configuration was opposite, but that didn't matter, since there was no heat sink involved.
So when you did the transistor pair (NPN and PNP), where they both having different gains, or just one transistor?

Sorry, I don't understand the question. I simply bought a pair on eBay, not sure matched or not, but I didn't notice the hfe rating. The current system on all channels, they seem to use -P option for MN2488, and -Y for MP1620

Do I need to match these and if so what do I need to do? is it impedance measurement? I just ordered one MP1620-Y

[R_J]

Re: Sony STR-DN1030 Distorted audio when Volume adjusted

These transistors are no longer manufactured by sanken, so who manufactured the ones you got?

The Sony sub part number was 8-749-010-26 (MP1620-OPY-M) and 8-749-010-25 (MN2488-OPY-M)

[CapLeaker]

Re: Sony STR-DN1030 Distorted audio when Volume adjusted

I had to match mine up, because the originals were not available for a long time (45 years) and the replacements I've chosen had a pretty wide hfe span. It's just an example I had to go through for one old amp I had to go through. I just hope this time you get the right ones.
So the MN2488 is exact the same than it supposed to be? It's just the MP1620 that was / is wrong?

[jason123]

Re: Sony STR-DN1030 Distorted audio when Volume adjusted

These transistors are no longer manufactured by sanken, so who manufactured the ones you got?

The Sony sub part number was 8-749-010-26 (MP1620-OPY-M) and 8-749-010-25 (MN2488-OPY-M)

I am buying Sanken parts from Ebay.

[jason123]

Re: Sony STR-DN1030 Distorted audio when Volume adjusted

I had to match mine up, because the originals were not available for a long time (45 years) and the replacements I've chosen had a pretty wide hfe span. It's just an example I had to go through for one old amp I had to go through. I just hope this time you get the right ones.
So the MN2488 is exact the same than it supposed to be? It's just the MP1620 that was / is wrong?

Yes, based on the markings on the part

[jason123]

Re: Sony STR-DN1030 Distorted audio when Volume adjusted

These transistors are no longer manufactured by sanken, so who manufactured the ones you got?

The Sony sub part number was 8-749-010-26 (MP1620-OPY-M) and 8-749-010-25 (MN2488-OPY-M)

When I try to see what these Sony Numbers translate to as far as manufacturer numbers, I see them listen as, for example: 8-749-010-26 is MP1620 with O, or Y, or P marking on the parts. All of these are very different hfe.

See:
https://www.genuinereplacementparts....kaAgdtEALw_wcB
https://www.unlimitedapplianceparts....-8-749-010-26/
https://www.amazon.com/-/es/Sony-OEM.../dp/B00FZXHHCQ

They treat these hfe differences as unimportant!

So is there a way to know what 8-749-010-26 is for a Sanken manufacturer number? which hfe is this number?

I'm going by the marking on the part I removed, which is Y. The one I erroneously installed is making P (less hfe.) I've ordered the Y. Do you think this is the smoking gun?

Y marking (the one use on all other channels as hfe range of 15,000 - 30,000
The P marking (the one I accidently installed) has hfe of 6,500-20,000

You'd think the distortion should not happen just because of this?

[CapLeaker]

Re: Sony STR-DN1030 Distorted audio when Volume adjusted

When replacing transistors volts on base / emitter is important. Hfe is important too. Depending on circuit, you might even want to match them! In this circuit I can see you don’t need a perfectly matched pair. But I really wouldn’t an NPN and PNP pair together that has a 100% difference in gain. I know of circuits where the Hfe on transistors went so low due to age, that the circuit stopped working as designed. But if I would measure the transistor in diode mode, I couldn’t tell the difference and things looked good. It only came about until I took the transistor out and started to measure hfe. Depending on circuit, yes, hfe does matter, specifically in parallel as one works harder than the other.
I’ve seen amps where the NPN and PNP pair were quite a bit off between them, but not like 100% off. That data sheet would suggest like 250% difference between that model what would be considered normal. Most other transistor data sheets do that too or even leave the maximum out. Look at a MJE15032.
If you want to shotgun things you’d need to replace a few resistors and a preamp stage too. If you really wanna know what’s going on and why, an oscilloscope is your best friend.

[jason123]

Re: Sony STR-DN1030 Distorted audio when Volume adjusted

When replacing transistors volts on base / emitter is important. Hfe is important too. Depending on circuit, you might even want to match them! In this circuit I can see you don't need a perfectly matched pair. But I really wouldn't an NPN and PNP pair together that has a 100% difference in gain. I know of circuits where the Hfe on transistors went so low due to age, that the circuit stopped working as designed. But if I would measure the transistor in diode mode, I couldn't tell the difference and things looked good. It only came about until I took the transistor out and started to measure hfe. Depending on circuit, yes, hfe does matter, specifically in parallel as one works harder than the other.
I've seen amps where the NPN and PNP pair were quite a bit off between them, but not like 100% off. That data sheet would suggest like 250% difference between that model what would be considered normal. Most other transistor data sheets do that too or even leave the maximum out. Look at a MJE15032.
If you want to shotgun things you'd need to replace a few resistors and a preamp stage too. If you really wanna know what's going on and why, an oscilloscope is your best friend.

I'd love to know what's going on.. however with the stacked boards assembled it's fairly tough to probe the main board without shorting the heck out of everything. So that's the risk I'm trying to avoid. But I do have an Oscilloscope!

Are the smaller transistors and their associated resistors what you're referring to as "Pre-Amp"? resistor values were checked to be within tolerance so that leaves the 2 small-sig transistors? Anything in particular that I have to get, since the SONY part numbers don't have good manufacturer number cross-reference?

[CapLeaker]

Re: Sony STR-DN1030 Distorted audio when Volume adjusted

Fix that what you know isn’t right then go from there. I am not a shotgun fan as such.

[jason123]

Re: Sony STR-DN1030 Distorted audio when Volume adjusted

Very unexpected, but i put the "new" part in and now i am getting protection error! Will swap main transistors between left and right and see if that follows the new Y MP1620

[jason123]

Re: Sony STR-DN1030 Distorted audio when Volume adjusted

Ok swapped FR transistors to the problematic channel (FL) and distortion is still happening on FL. Resistor values are good. I dont have a way to test small BJTs. Should i replace all smaller BJTs? Any matching there?

[budwich]

Re: Sony STR-DN1030 Distorted audio when Volume adjusted

Hopefully, you can get back to having the one working front channel (FR). IF so, before you go further in "tearing apart" your board / components, do some "simple resistance" checks. Unplug / disconnect the receiver from power. Get access to the main board as outlined in the SM (page 33/34) which shows the FR / FL. Choose "wisely" various points to compare a resistance measurement across the two different circuits... you aren't looking for "absolutes"... you are looking for "similar". Yes, I know you indicated you did an "impedance check" but that was likely at the outputs and was a "gross" check of the "entire circuit". The checks that you want to do now, are more "partitioned" to try isolate a group of components / portion of a circuit that you can then focus on specifics (individual components) there after. It might not show anything BUT something could readily pop out. It basically costs nothing other than a bit of time.

The reference points for the checks could be grounds or powering or even in / out lines depending where in the circuit you choose. The thing about doing this method is there is little to no danger in cause damage to the board / circuit (short, breaking track, etc) because nothing is being powered.

Study the circuit diagram to choose your points to isolate / test various sections that can be readily compared across the good and bad front channels. Make notes on what you observe from your meter and which test points you were using at the time.

Since you have "touched" some of the active component, that area might be your first focus.

Hope this helps.

[budwich]

Re: Sony STR-DN1030 Distorted audio when Volume adjusted

As an example of a possible check. do a resistance measurement to ground of the voltage outputs on the IC701 (page 34)... pins 2,3 and 13,14... these are signal outputs going to the subsequent components in the output stages. You can compare the meter readings / response to see if there is significant difference. Go from the result.

Note: if you can't readily get at the IC points move along the diagram to a readily accessible area / component and measure there.

[jason123]

Re: Sony STR-DN1030 Distorted audio when Volume adjusted

So, one additional observation that may mean something to you: when the system is playing, Volume level 1 for this FL channel is very high compared to the other channels that you can barely hear anything out of.

Here is today's work:.. swapped main BJTs, Smaller pre-amp ILIMITER (Q702, and Q701) between the FR (Good) to FL. No change. FR still works fine, FL still has issues.

Verified R707, R706, R709, R710 all comparable to FR and match values on schematic.
Seems the only thing that remains unchecked:
Post amp circuit and IC701
Thoughts?

[budwich]

Re: Sony STR-DN1030 Distorted audio when Volume adjusted

capacitor issue maybe. Again, the suggested resistance "probing" may point to an area of difference including ic701.

additionally, with the "new observation", get your scope going. Feed in a 1khz tone of known value. Look at the resulting output characteristic.... voltage / frequency / appearance.

[jason123]

Re: Sony STR-DN1030 Distorted audio when Volume adjusted

Started with impedance measurement around IC701. All impedance measurements were referenced to pin 7 (gnd). No significant differences between IC601. Some pins had caps so impedance was fluctuating... but similar to bad channel.

Attempted 1khz sinewave input, however relays were not routing signals unless all boards were connected and that gives almost zero room to probe with 3 board stack.

Finally went for the jugular and swapped ic701 with ic601. Problem remained on the FL channel. Checked resistor and cap values around the IC. All seem to check out.

That leaves post amp circuit? Not sure how that could be it but i am new to this audio stuff so help is very much appreciated

[budwich]

Re: Sony STR-DN1030 Distorted audio when Volume adjusted

I think you misunderstand what I was saying about the 1khz input. You mentioned that you have distortion in the original post. What does that mean? Further, you indicate that you have good sound out of all channels other than FL.... that means you are able to input sound somewhere and output it somewhere... so that is what I am asking you to do. Input a 1khz sound (from a computer file / cd disc / dvd audio setup disc... whatever). Look at that input on your scope to ensure that you are reading exactly what is being input (it should look like a nice sound wave with known frequency and voltage specification). Then look at the resulting output wave form on both a good channel and the bad channel. What characteristic is your scope showing.... that is what I am referring to. From that, this will tell us what the "distortion" that you are conveying... ie. voltage clipping, square wave, no wave, no set frequency, what.

Further, the FL and R are only on ic701 so you likely only need to be concerned with those.

Hopefully, your scope view of the output will provide more information to add to your observation about loudness of the bad versus others.

Further note, that the tests suggested on IC701 were just samples... as mentioned, other strategic points can be used to compare across R and L circuits to look for differences.