Troubleshoot Sanyo DCX-3300ka Amp section

[jimkarl]

Have a Vintage sanyo receiver with no audio/channel hum on left front channel. Traced goo audio from the preamp board to the amp board. Amp board schematic attached. Pin Voltages on the main Amp IC are (with right channel included as a comparison):
Pin L R
1 GND GND
2 45.8 22.9 Pin to 1000uf coupling cap
3 46.3 46.3
4 45.8 35.1
5 N/A
6 N/A
7 10.1 23
8 45.8 23
9 18.9 22.9
10 44.5 44.5

Good audio and voltage (12V) at the TR5 emitter output. But on the other side of C503 at input pin 8 of IC501 (STK STK0231), it jumps to 45.8v, when it should be 24v. Also with pins 2 & 4 also at 45.8V, it makes me think that IC501 is fried. Thoughts? I want to be 100% sure not missing anything since that's a $25 part replacement. I've checked all the resistors and caps and they all seem good and in spec. Also weird is the Pin 9/7 combo. Should be 24v on both pins but on Pin 9 is 18.9, then on the other side of R 513 it's 17.9, then on the other side of C511 it drops to 10.1v. R513 checks out ok and I even swapped C511 to be sure (no difference).

[Longbow]

Re: Troubleshoot Sanyo DCX-3300ka Amp section

At first glance you may in fact have a bad output IC. Personally I would look at the IC block diagram, since troubleshooting a rectangle is difficult to do. The input and output pins are latched to the supply so a shorted IC is likely.

[budm]

Re: Troubleshoot Sanyo DCX-3300ka Amp section

Do you have the rest of the service manual?
I would check the resistance between pin 2 and pin in both direction with an Ohm meter to see what you get.

[jimkarl]

Re: Troubleshoot Sanyo DCX-3300ka Amp section

At first glance you may in fact have a bad output IC. Personally I would look at the IC block diagram, since troubleshooting a rectangle is difficult to do. The input and output pins are latched to the supply so a shorted IC is likely.

Unfortunately no detailed breakdown for the IC other than it's an STK-023. Nor datasheet to be found on the internet anywhere, including the manufactures I could find that still can source the obsolete part. How ridiculous is that?

[jimkarl]

Re: Troubleshoot Sanyo DCX-3300ka Amp section

Do you have the rest of the service manual?
I would check the resistance between pin 2 and pin in both direction with an Ohm meter to see what you get.

I purchased the entire service manual. Nothing more relative to the circuit. Just typical board layouts, parts list, tuner stringing etc. . Between pin 2 and WHAT? You left the 2nd pin # out to check against.

[Longbow]

Re: Troubleshoot Sanyo DCX-3300ka Amp section

Is this a Quadraphonic thing? I see mention of trouble in the 2/4 channel switch if this is the case...worth checking out. One point to consider is that a shorted output IC (the most common way to fail) will draw lots of current and blow a fuse or fry a part. You don't have those symptoms.

[budm]

Re: Troubleshoot Sanyo DCX-3300ka Amp section

I purchased the entire service manual. Nothing more relative to the circuit. Just typical board layouts, parts list, tuner stringing etc. . Between pin 2 and WHAT? You left the 2nd pin # out to check against.

Sorry, pin 2 and pin 3 which should be the VCC pin of the IC but since the diagram is not complete I cannot really tell for sure.The DC at the output pin should be 1/2 of the VCC.

[jimkarl]

Re: Troubleshoot Sanyo DCX-3300ka Amp section

Is this a Quadraphonic thing? I see mention of trouble in the 2/4 channel switch if this is the case...worth checking out. One point to consider is that a shorted output IC (the most common way to fail) will draw lots of current and blow a fuse or fry a part. You don't have those symptoms.

Since there's audio going into the chip, and none at either speaker or the headphone jack (which immediately follows, not seeing how the switch could play a role.

[jimkarl]

Re: Troubleshoot Sanyo DCX-3300ka Amp section

Sorry, pin 2 and pin 3 which should be the VCC pin of the IC but since the diagram is not complete I cannot really tell for sure.The DC at the output pin should be 1/2 of the VCC.

It's showing a short. that's in circuit of course, but the other channel IC in circuit doesn't show a short.

[Longbow]

Re: Troubleshoot Sanyo DCX-3300ka Amp section

0 ohms between pins 1 and 3: means your IC is shorted as suspected. There is one on ebay currently. I used to have an STK cross reference but I forgot where I found it. I'm sure there a subs that would work fine, just be sure it is a mono amp and that the pins match. You might also find a scrap unit for less money than buying the one IC. Be sure to lift the coupling cap (negative lead of C517) as a double check.

[jimkarl]

Re: Troubleshoot Sanyo DCX-3300ka Amp section

0 ohms between pins 1 and 3: means your IC is shorted as suspected. There is one on ebay currently. I used to have an STK cross reference but I forgot where I found it. I'm sure there a subs that would work fine, just be sure it is a mono amp and that the pins match. You might also find a scrap unit for less money than buying the one IC. Be sure to lift the coupling cap (negative lead of C517) as a double check.

You meant between pins 2 & 3 right?

[jimkarl]

Re: Troubleshoot Sanyo DCX-3300ka Amp section

0 ohms between pins 1 and 3: means your IC is shorted as suspected. There is one on ebay currently. I used to have an STK cross reference but I forgot where I found it. I'm sure there a subs that would work fine, just be sure it is a mono amp and that the pins match. You might also find a scrap unit for less money than buying the one IC. Be sure to lift the coupling cap (negative lead of C517) as a double check.

even though I had checked C517 previously, I pulled as you suggest just to triple check - no change. Definitely a short in the chip.

No obviously substitutions as far as the sanyo pages tell me (whereas other STK model did have replacements. Pulled the chip apart but fair to say "no user serviceable parts here - unless you are working under a microscope LOL.

I have an overseas source a little cheaper then the one on ebay, but still will be in for $20 ($10 part , $10 shipping). I just hope nothing else in the circuit is the contributor to the failure, as I certainly don't want to kill the new one when I put it in!

[Th3_uN1Qu3]

Re: Troubleshoot Sanyo DCX-3300ka Amp section

It's not that bad - the power outputs is likely what went short, and i have seen pics of people drilling holes in the STK hybrids, cutting off the wires to the internal power transistors and connecting regular ones to it.

The best option is to replace the whole module but beware, lots of fakes on ebay. Most of them do work to some degree but they will not be as rugged as the original one, nor sound as good.

[jimkarl]

Re: Troubleshoot Sanyo DCX-3300ka Amp section

Been a while for this post, but my IC501 finally came in. Replaced it and same problem. Hum (only) in left channel.
IC 501 pin readings
Pin Voltage
1 0
2 45.6
3 45.7
4 45
5 N/A
6 N/A
7 45
8 44
9 44
10 45

Triple checked the caps on that channel - all are good and I even swapped out the output ones just in case. Also triple checked the resistors. measured the TR501 transistor that feeds Pin 8. B= 12.4, C=24, E = 11.9 all similar to right channel. Pulled transistor and tested on tested and checks out good., no leaks. There's good audio at the emitter and same audio quality as the right channel but that Pin 8 of IC501 is Twice what it should be, as are the 9/7 and 2/4 pins.

Any idea what is going on? Did I get a bad IC chip (would piss me off as I paid $20 for it.) Did it go bad when I put it in the circuit? Or is there something in this cicruit that I have missed that is driving one pin too high and being reflected on all the other pins as a result?? Really stuck now.


https://drive.google.com/file/d/0B_Y...ew?usp=sharing

[Longbow]

Re: Troubleshoot Sanyo DCX-3300ka Amp section

Pin 7 and pin 9 are now showing different voltages than previously. They don't seem to suggest anything to me. I would troubleshoot this as a d.c. problem. At this point I would suspect a cracked traces, solder blob, cold solder or other open connection. We hope that the new IC was actually what is says, and that connecting it in the circuit did not blow it up.

Ground the volume control wipers. Open and pull up the (-) end of the output coupling capacitors. With power off, confirm continuity between pins and parts. With power on and voltmeter monitor on pin 2, wiggle the parts, warm them up, etc. watching for voltage change on pin 2.

The input voltage on pin 8 is at the rail. Since the IC's job is to follow the input, the IC is trying to do its job - at least at d.c. Another possible source of information is to (power off) measure d.c. resistance between the IC pins and ground (note them down). Then take the same resistance measurements from an IC on a working channel. Don't rule out a leaky input coupling capacitor.