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My Rotel RC-1070 stopped powering up after several static…

Customer Question
My Rotel RC-1070 stopped...

My Rotel RC-1070 stopped powering up after several static shocks yesterday. I remember this happened before but corrected itself after I left it unplugged for awhile and tried again. Not this time though. What can I check inside before bringing it to service?

Technician's Assistant: What's the make/model of your device? How old is it?

Model RC-1070. Its about 10 yrs old

Technician's Assistant: How long has this been going on? What troubleshooting have you tried?

Since yesterday. Moved to a much dryer climate last and I got a couple static shocks yesterday that may have caused it.I have let it sit 24 hours and tried to power up. Took cover off but only looked around inside so far.

Technician's Assistant: Anything else you want the Electronics Expert to know before I connect you?

I still get the standby light and the volume control lights up as well.

Submitted: 7 months ago.Category: Consumer Electronics
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Answered in 15 minutes by:
11/13/2017
Electronics Technician: Louie, Technician replied 7 months ago
Louie
Louie, Technician
Category: Consumer Electronics
Satisfied Customers: 13,369
Experience: 25+ yrs. experience in the field and 5+ yrs. online, down to component level.
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Hi and welcome to JustAnswer, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.
Initially, please post back with clear pictures of the inside circuitry since ".... Took cover off ..." Click HERE.
http://ww2.justanswer.com/help/how-do-i-send-photo-or-file-expert-hl
These pictures would then serve as common references allowing me to see what you are seeing.

This is an independent site and members of this online community provide information, repair tips, technical assistance as a form of paid Q & A service.

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Customer reply replied 7 months ago
5 pics enclosed. Let me know if they are clear enough.
7BA1D556-23BE-4E3B-B293...jpeg7BA1D5...jpeg740D8152-F799-4D9B-A5B5...jpeg740D81...jpeg4A765EF0-A976-490E-85BF...jpeg4A765E...jpegEECEE925-05DA-43E1-85B1...jpegEECEE9...jpeg972DB84A-E6FA-48B6-9015...jpeg972DB8...jpeg
Electronics Technician: Louie, Technician replied 7 months ago

Appreciate the pictures.

With the RC-1070 plugged in and turned on, What are the AC voltages of connector CON4:

  • red to red;
  • red to black;
  • blue to its black

A friendly reminder: voltage measurements by its very nature requires that the unit be plugged in and turned on. It is therefore LIVE! Please exercise due care and caution.

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Customer reply replied 7 months ago
The unit is plugged in but will not turn on. I do have standby light on. I get nothing with my voltage tester on any color combination. Should I be using a multi meter?
Electronics Technician: Louie, Technician replied 7 months ago

Yes please; use a multi-meter.

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Customer reply replied 7 months ago
Red to red;41.6
Red to black; 20.6
Blue to black 11.6
Electronics Technician: Louie, Technician replied 7 months ago

Please check the voltages:

  • at pins 1 and 3 of IC901;
  • collector and emitter of transistor Q904.
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Customer reply replied 7 months ago
IC901is 19.8
Looking for Q904
Customer reply replied 7 months ago
Q904 is 0.7
Electronics Technician: Louie, Technician replied 7 months ago

Sorry, there should be two (2) readings from IC901; pin1 and then pin 3

Likewise with Q904; i.e. voltage reading at its collector and then at its emitter.

...inputs and then at their outputs.

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Customer reply replied 7 months ago
Having trouble with this webpage. Are you still there?
Electronics Technician: Louie, Technician replied 7 months ago

Yes, still here. Were you able to carefully check the voltages at:

  • pin1 and pin 3 of IC901; and
  • collector and emitter of Q904?
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Customer reply replied 7 months ago
Hopefully my pic went through. The label for the transistor is on the other side of the drawing. This is how I measured it. Not sure which is pin 1 or 3 but I measured the outsides using the center pin. I got 10.1 and 32.3. I will do the same for Q904 with a pic. Not sure which is collector and which is emitter. Will that work? I am newbie at this but I think I can handle it with a little patience. Thanks.
Electronics Technician: Louie, Technician replied 7 months ago

Use the chassis ground as common reference.

With IC901; tab with hole is the back hence front left pin is 1, middle is 2 and right is 3.

From 1 of the pictures provided, it would appear that Q904 has its base marked with a "B". Thus with the flat side facing you, left leg is emitter, center is collector and right would be base.

Exercise caution as it is easy to miss a leg and inadvertently short the 2 pins of the parts.

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Customer reply replied 7 months ago
At Q904 emitter is 24.1 and collector is 31.1
At IC901 pin 1 is 32.5 and pin 3 is 10.6
Electronics Technician: Louie, Technician replied 7 months ago

Please re-check. The expected readings are:

  • pin1 of IC901.......+14.5V;
  • pin 3 of IC901.......+5.8V;
  • collector of Q904....+13.4V; and
  • emitter of Q904.......+12V.
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Electronics Technician: Louie, Technician replied 7 months ago

Try using the range 20 of the V-- not the V~

Yes, that would be pin 1 of IC901

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Customer reply replied 7 months ago
Pin 1 of IC901 is 15.08
Pin 3 is 5.38Emitter of Q904 is 11.41
Collector is 14.48
Electronics Technician: Louie, Technician replied 7 months ago

Locate connector JP1B.

Ensure that all the wires are properly/securely inserted and locked in place.

Measure the voltages from all its pins. Pin 1 has a circle mark.

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Customer reply replied 7 months ago
JP1B
Pin 1 is 4.09
Pin 2 is 0
Pin 3 is 11.41
Pin 4 is 5.37
Pin 5 is 0
Pin 6 is 0
Customer reply replied 7 months ago
Did I lose ya?
Electronics Technician: Louie, Technician replied 7 months ago

Thank you for your patience; had to step out.

Please try measuring the voltage of pin 2 again while pressing on the STANDBY button.

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Customer reply replied 7 months ago
Pin 2 is 4.08 with the standby button pressed.
Electronics Technician: Louie, Technician replied 7 months ago

And do the same for pin 5; i.e. re-measure while pressing on the STANDBY button.

Thanks.

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Customer reply replied 7 months ago
Pin 5 is 0 with the standby pressed
Electronics Technician: Louie, Technician replied 7 months ago

This last reading is very critical as this is the signal that drives the relay transistors to turn on the RC-1070. This signal is provided for by the CPU TMP47C400BN-1A57.

At this point, the housekeeping-logic circuitry including the CPU itself is highly suspect.

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Customer reply replied 7 months ago
the 0 at pin 5 makes you think it is the CPU. Do I just replace the CPU (if I can find it) or is there more to it? The component looks fine. Would it show any signs if it was bad? Can it be tested? Not sure what you mean by Housekeeping -logic circuitry.
Electronics Technician: Louie, Technician replied 7 months ago

The "Housekeeping -logic circuitry" is the electronics that interprets the remote control commands and/or the manual front panel controls as well as the rudimentary functions such as supply power to the volume control motor, muting and yes, even turn on by trigerrin g the relay transistors to enable the relays. The relays in turn switch on the power to the other circuitry.

The CPU works like a brain and takes into consideration several factors before turning on a command into an action.

Absence or incorrect 'factor' would cause the CPU to halt the execution of a command such as pressing on STANDBY button but still would not turn on the relays.

1 such factor is the time base controlled by the crystal oscillator X701. Absence of this time base would cause the CPU to 'not work'

The only easy tests would be to:

  • check for Vcc +5.0V on pin 42 of IC701 using the multi-meter;
  • logic HI @ pin 8 when pressing on the STANDBY button using a logic probe;
  • and on pin 36;
  • time base waveform at pins 31 & 32 using an oscilloscope;
  • initialization pulse @ pin 34;
  • logic conditions of the other pins.
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Customer reply replied 7 months ago
Absorbing and researching all that while I cook and feed the family. Will you keep working with me on this? About all I can do is check the pin 42 with my multi meter (if I can figure out where pin 42 is). I don’t own the other testers you mentioned. Get back to you on that.
Customer reply replied 7 months ago
I will be picking up a logic probe tomorrow to check what I can with that.
Electronics Technician: Louie, Technician replied 7 months ago

Pin 42 would be off to 1 corner, the last pin.

And yes please, an update when conveniently able.

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Customer reply replied 7 months ago
Hi Louie it's Steve again. Thanks for sticking with me. I will keep rolling with this project if you will. I spent the morning looking in vain for a logic probe around town. I ordered one from Amazon and it should be here tomorrow. I printed out my own schematic and located/rechecked everything that we've done so far. I got 4.75 v on pin 42 at IC701. I'm not sure how you got that value as I don't see it indicated on my schematic. I see from the schematic that pin 5 at JP1B should be 1.5 v and its 0. Is that why you say that the cpu is highly suspect? Are we testing X701 at pins 31 and 32 with an oscillator to try and eliminate the CPU as culprit? As I said I'm newbie but learning. Thanks for your patience.
Electronics Technician: Louie, Technician replied 7 months ago

4.75 v on pin 42 at IC701...not sure...don't see it indicated on my schematic - follow/trace back connections through D722 to pin 4 of JP1A where pin 4 of JP1B is +5V.

Yes, +1.5V @ pin 5 of JP1A/B from pin 36 of IC701 is expected upon pressing of the STANDBY button. That it is 0.0V even if STANDBY button is pressed would mean that the CPU is not allowing the turning on of the RC-1070

...or, the CPU is faulty.

Yes, X701 test on pins 31 & 32 preferably with an oscilloscope. In the absence of a scope, try voltage measurement.

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Customer reply replied 7 months ago
Hi. Still waiting for the probe. Mail hasn’t been delivered here yet. I’ve been practicing my soldering to prepare for the repair. Hopefully we can ID the culprit so I can fix it. Thanks for the help so far and I will hopefully have some more info for the search tonight or tomorrow
Electronics Technician: Louie, Technician replied 7 months ago

Appreciate the update now and again when able.

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Customer reply replied 7 months ago
Hi Louie. Something unexpected happened today when I was checking values with the logic probe. The unit powered up. I had checked all the pins on IC701 already and was getting ready to double check all my readings.. I was trying a different positive supply to the circuit and when I plugged the unit in I heard a relay click and suddenly power. I haven't hooked up an amp to it yet but its definitely powering up as normal. I checked pin 5 at JP1B and it reads 0 on its own. When I press stby it reads 1.4v and stays that way when it is powered up. I went ahead and took all my values at IC701 again. Do you want all those numbers? One oddball I found was pin 31 reads low toggle/pulse when powered on or powered off but if I push the stby button while holding the probe to the pin the power will not come on. If I push it again it will power up. It seems the measuring is interfering with the power up. Now that the unit is powering up will I still be able to find the culprit?
Electronics Technician: Louie, Technician replied 7 months ago

Consider a 'shotgun' approach; i.e. carefully re-solder all the pins of IC701 including the earlier posted time-base crystal X701.

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Customer reply replied 7 months ago
Okay. I will try that. I am going to practice a bunch more first. I don't want to damage anything in my unit. I will get back to you when I finish. FYI I was wrong when I said the unit is powering up normally. I noticed that the indicator light on the volume knob stays dimly lit when the unit is off. I don't think it did that before it broke. I think I will put the pre amp back in the system while I am practicing my soldering technique to see if it works.
Electronics Technician: Louie, Technician replied 7 months ago

I understand and yes please.

For insight, I normally use a hot air solder station for similar re-touch / re-flow work. Click HERE.

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