Sparkplug
Super Member
These had to be changed anyway. The IR module cap should do it. Check the solder joints inside that module while you have the top off.
RX-770 Remote control issue. Works briefly after cycling receiver power.
- Thread starter RS-MN
- Start date
I edited my last post with images of the IR receiver. See images. Not sure what to do with it. No conventional Cap there.
Sparkplug
Super Member
Yes, there are only two surface Mount caps and no electrolytics. If the solder work looks good, put it back together as I doubt if the LED is bad, they usually don’t go bad.
I've looked at it under a magnifying glass and all joints look solid. I'll re-assemble and re-install it tomorrow.
One interesting thing is when the receiver is off for a while (few hours), the remote works longer (10-15min) after initial plug in.
The remote works for only a 2-5 minutes if re-powered soon after that initial power up.
Sparkplug
Super Member
I think U301 voltages need to be checked/monitored using your neighbor’s oscilloscope before after the failure occurs. Need to find out what happens to the received remote control signal. For starters, maybe monitor U301 pins marked Vc and Vd(?) to see what happens to them during the failure. Also, keep double checking the solder work related to this chip from the power supply that provides the +12V all the way to the regulator that puts out +4.8V (Q317).
Good work.
This reeks of a bad solder joint, cap, or diode somewhere. To narrow it down, need your neighbor’s oscilloscope. If someone has specific experience with this issue, I’m sure they’ll chime in.
Good work.
We'll keep checking it out. I did check Pin1 and it was 4.778V before and after failure. It has been running at that value since we started checking this receiver. We'll get the scope back out and check the other pins.
Sparkplug
Super Member
Sounds good. I’ll have another look once I get back to my lab a bit later on. On the train now.
Sparkplug
Super Member
Try monitoring U301 middle pin (marked Vo or Vd, can‘t tell) and pin 17 of the μ-processor U306 (they’re directly connected) while the issue happens. They should read the same at all times. If not, investigate the trace/cable connecting them plus the solder work. Pin Vc of the U301 should always be 4.8V (its power line).
Edit: Pin G of U301 is ground, please check its solder joint.
Edit: Pin G of U301 is ground, please check its solder joint.
Last edited:
Sure sounds like either a bad solder joint or a cap heating up and doing something strange.
Check the VCC (4.8V) with the 'scope -- if you have significant ripple or intermittent voltage drops, the computer will restart constantly every time the voltage drops below about 3V.
Suspect ALL the electrolytic caps in the circuit, they've been energized for quite a while now!
Check the VCC (4.8V) with the 'scope -- if you have significant ripple or intermittent voltage drops, the computer will restart constantly every time the voltage drops below about 3V.
Suspect ALL the electrolytic caps in the circuit, they've been energized for quite a while now!
It sure seems like a cap heating up and acting strange someplace. Voltage has no drops or ripples that we've seen. It's a steady voltage at the IC whether the remote works or not.
C388 (0.47uf) seems to be in the path (not sure which others), but with the voltage not changing, I don't think it's bad? Suggestions for other caps to check would be welcome.
The remote still works for 20-30 minutes until it quits when first started, but less that 5-10min if cycled after that.
I've ordered an IR Receiver (GP1U501X). I'll swap that out when it gets here and see if that has any affect.
C388 (0.47uf) seems to be in the path (not sure which others), but with the voltage not changing, I don't think it's bad? Suggestions for other caps to check would be welcome.
The remote still works for 20-30 minutes until it quits when first started, but less that 5-10min if cycled after that.
I've ordered an IR Receiver (GP1U501X). I'll swap that out when it gets here and see if that has any affect.
Sparkplug
Super Member
What happens at the middle pin of IC301, the one that connects to the u-processor (pin17)? Is there any data on it after failure? You’d have to operate the remote control while monitoring REM pin of U301 on the oscilloscope. If no activity, then the problem is most likely inside U301 or its inside connections.
Last edited:
Still waiting to get some time with my neighbor and his scope again.
I re-soldered a bunch of things around the IC and the Cap that was replaced with the super Cap and where the wires come in from the IR receiver. I need a smaller tip before I try to re-solder the IC. pins
The new U301 should be here in a few days.
I re-soldered a bunch of things around the IC and the Cap that was replaced with the super Cap and where the wires come in from the IR receiver. I need a smaller tip before I try to re-solder the IC. pins
The new U301 should be here in a few days.
It's fixed.
The IR receiver part (U301) came this week and I installed it tonight. The RX-770 remote has been working as it should all evening.
Thanks everyone for your help!
I learned a lot.
The new IR receiver is the one listed in the service manual. New one is on the left in the images.
The IR receiver part (U301) came this week and I installed it tonight. The RX-770 remote has been working as it should all evening.
Thanks everyone for your help!
I learned a lot.The new IR receiver is the one listed in the service manual. New one is on the left in the images.
