Korg DTR-1000 Tuner advice please...  [schematic]

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ryanuk
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Post by ryanuk »

Hey

I obtained a KORG DTR-1000 from ebay. Attempting to fix it.

There is no input getting to the tuner section. Power and tuner lights come on. I've confirmed that the power supply, and mute relay circuit is all working correctly.
So that leaves the FET/Op Amp input to the tuner. Using signal tracing I've confirmed the faulty component is the BA10358F op amp. I get a signal at pin 2, but no output from the first 1/2 of the op amp.

BA10358F is now obsolete. Its a 'ground sensing' dual ap amp. Finding it hard to understand the difference between this an any other op amp. Schematic (attached) doesn't suggest its doing a special function.

Can someone help with these questions?
1. Could I sub the BA10358F with a LM358 (which google suggests can be a replacement)?
2. Would any dual op amp suffice?
3. What is a ground sensing amp?
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KORG DTR-1000.png

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mauman
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Post by mauman »

Yes, an LM358 will work fine, it has a similar supply voltage range, offset voltages and bias currents. Ground sensing means that with a single supply voltage (like +9V and ground), the input can go as low as the negative rail = ground, but not necessarily as high as the positive rail = 9V. Rail to rail means the signal can go both ways, ground sensing means it can go to the negative rail only. The LM358 will do ground sensing too.

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ryanuk
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Post by ryanuk »

mauman wrote: 26 Sep 2022, 21:57 Yes, an LM358 will work fine, it has a similar supply voltage range, offset voltages and bias currents. Ground sensing means that with a single supply voltage (like +9V and ground), the input can go as low as the negative rail = ground, but not necessarily as high as the positive rail = 9V. Rail to rail means the signal can go both ways, ground sensing means it can go to the negative rail only. The LM358 will do ground sensing too.
mauman - works out well as the BA10358 IC is getting expensive, and I happen to have a new SMD LM358 in my parts bin!

Thanks for the explanation - so ground sensing Op amps are designed for single rail, and are more sensitive toward the negative rail?

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Post by Manfred »

An alternative would be to use the SMD version of the BA10358F the BA10358F E2, and solder it to a SOP8 to DIL-8 adapter.
You can find the BA10358F through-hole version on the net, but only very expensive and from countries where you have to be careful not to buy a fake.

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Post by mauman »

ryanuk wrote: 27 Sep 2022, 07:55
Thanks for the explanation - so ground sensing Op amps are designed for single rail, and are more sensitive toward the negative rail?
Right. See the "Input Stage Concerns" section in this application note: https://www.maximintegrated.com/en/desi ... 6/656.html

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Post by ryanuk »

Manfred wrote: 27 Sep 2022, 08:52 An alternative would be to use the SMD version of the BA10358F the BA10358F E2, and solder it to a SOP8 to DIL-8 adapter.
You can find the BA10358F through-hole version on the net, but only very expensive and from countries where you have to be careful not to buy a fake.
Manfred. Its actually an SMD version of the BA10358F that is needed. However, they are not readily available in the UK. I can buy from china (for about $2!) but wary of fakes.

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Post by Manfred »

Hi Ryanuk.
The BA10358F is available in the UK.

https://www.digikey.co.uk/en/products/d ... hALoC%2BQA

https://www.mouser.co.uk/ProductDetail/ ... RizA%3D%3D

Also available in other SOP-8-XX packages at these dealers, I do not know which package you need.

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Post by ryanuk »

Sure but the shipping is $12 :shock:

Thanks through manfred

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Post by Manfred »

I am sorry that this does not help you.
It is often the problem of the minimum order amount,
there remains only the possibility to order other items to exceed this limit.
Remains only to buy the IC somewhere cheap and hope that it is not a fake.

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Post by ryanuk »

Manfred wrote: 27 Sep 2022, 21:07 I am sorry that this does not help you.
It is often the problem of the minimum order amount,
there remains only the possibility to order other items to exceed this limit.
Remains only to buy the IC somewhere cheap and hope that it is not a fake.
Absolutely - I dont order from Didikey or Mouser often. The delivery costs are too high for the hobbyist.
The other thing is, I bought the tuner itself for only £20 (~$20 :shock: ). So I dont want to spend too much money on it.
I think I will try the LM358 to see if the unit works. If so, there is a UK seller on ebay who can provide a BA10358 SMD for $5. I might get one of those if the unit proves worthwhile.

RyUK

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Post by ryanuk »

So, I had a frustrating evening with this project.

I managed to get the op amp off quite easily. Fitted an LM358... still no tuner. There appeared to be a very distorted signal at the opamp pin 7 output. I traced this distorted signal to the tuner input. So it appears to be getting to the processing IC.

After checking a few voltages elsewhere, I came back to the LM358... and then could not get an output!???

I was beginning to think the original BA10358F IC was ok. So I put the BA10358F back in. No output at all at Pin 7. Pretty sure this chip is dead.

So swapped it for an LM258. Now I have an output again from the buffer circuit. But again its very distorted.

Any ideas?? Full schematic attached.

I can't imagine the processor IC is dead as all the lights come on in the test mode (which are triggered by the processor). And when I select the tuning mode I can get the display to strobe and cycle through all the modes. It seems to be operating ok; Im convinced that its just not getting the right signal.
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mediy
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Post by mediy »

It is a bit hard to know what to look for - the tuner itself may not in fact be using/needing a clean signal - there may be some analogue processing going on to make it more suitable for the processor. Having said that I would be tracing the audio input with an audio probe just to see/hear what is going on.

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Post by x-tn »

ryanuk wrote: 26 Sep 2022, 19:32...Power and tuner lights come on. I've confirmed that the power supply, and mute relay circuit is all working correctly.
ryanuk wrote: 28 Sep 2022, 22:43...There appeared to be a very distorted signal at the opamp pin 7 output.
...
So swapped it for an LM258. Now I have an output again from the buffer circuit. But again its very distorted.
Did you check the voltage divider circuit (R3, R4, C20) that is connected to opamp pins 3&6? Maybe that 6.3V C20 is busted?
How did you confirm the power supply is working correctly?

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Post by ryanuk »

@X-tn @mediy

Thanks for your responses.
I'm going to sit down later and work through the schematics.
They are a bit hard to follow with 5v power rails being routed all over the place across the different boards.
In one instance 5v is being supplied to the from board at 2 places, so need to check these traces.

Will also look for shorts to ensure signal isn't being lost anywhere.

Going to check all the connector cables and make sure sure connections are being made between all the busses.
Not checked that voltage divider but I will later.

Also, I'm going to look closer at the eprom reset supervisor IC and make sure that it's working. Not familiar with these but I'll try and figure it out.

I have ordered the correct op amp out of desperation. The original was absolutely faulty. But Im not confident the unit will function once I've replaced it.

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Post by bmxguitarsbmx »

That ba10358 has some serious gain. making some square waves for sure. Maybe it has clipping properties that are special

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Post by ryanuk »

So, update on this.
I replaced the BA10358 op amp. Getting a good output. Still distorted but less harsh. I don't have a scope so cant "see" it, but this op amp stage is clearly boosting the signal prior to measurement in the microprocessor EPROM.

I've checked all the power rails for correct voltages and shorts. I've checked all on board ICs which appear to be working (save for the EPROM MPU?) All the switching logic and relay are working fine.

I can trace the audio input to the EPROM. And power gets to the EPROM. I have to conclude the EPROM is damaged.

Korg have spare boards. Ive managed to convince a UK service centre to purchase one on my behalf. Fingers crossed.
I would have loved for this to be simple component level swap out. Hate having to sub a whole board.

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Post by bmxguitarsbmx »

Way to stay on this repair! The output of that op-amp should be square waves. It is easier to count the period if it is a square wave. It may even be going into a digital input. No analog input needed. Best of luck! I think the Korg DTR1000 is a cool tuner. It looks cool at least. I have the DTR2000 and it is cheesy looking with molded plastic and bright blue LED's. Blue LED's harsh my mellow.

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Post by ryanuk »

Final update:
Received the "new" board; I say "new" as the part is NOS and labelled 2014! The replacement had a lot of dulled solder joins and residue around the connectors. So needed some cleaning.

Fitted it - tuner works. However one segment of the LED display was not functioning. I traced this to a poorly soldered through-hole jumper. Fixed.

Really pleased to report that the tuner is now at full working order!!
bmxguitarsbmx wrote: 07 Nov 2022, 16:13 Way to stay on this repair! The output of that op-amp should be square waves. It is easier to count the period if it is a square wave. It may even be going into a digital input. No analog input needed. Best of luck! I think the Korg DTR1000 is a cool tuner. It looks cool at least. I have the DTR2000 and it is cheesy looking with molded plastic and bright blue LED's. Blue LED's harsh my mellow.
@bmxguitarsbmx - my only gripe is that replacement board they sent is blue/white LEDs opposed to the original red/green. It could sub the LEDs from the old to new board. Id rather enjoy the tuner for now though.

Really pleased to report that the tuner is now at full working order!!

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