Hitachi radio coil replacement

[hr369]

You checked the speaker balance to see if that speaker channel is ON?   When you reversed polarity did you smell anything burning or see smoke?

[hr369]

Your wiring sounds correct on everything and no the cap on the volume is probably not the problem. Like I said, check the speaker balance. Yea i know that sound too simple but you can get really caught up in

thinking it's other things and not realize the most obvious. If that's not it then i would start looking at the amplifier circuit.

[gotham22]

Speaker balance doesn't seem to matter happens on both speakers. In looking at the two ha1339 ic's I am getting power to them but some of the pins are showing a higher voltage then the schematic says. Could these be blown?


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[hr369]

Can you draw a diagram of what pins you tested and what voltage they were?   How big of a variance was there compared to the schematic?

I can check your voltages against those in my radio if it's not too difficult to get at.

[hr369]

Can you draw a diagram of what pins you tested and what voltage they were?   How big of a variance was there compared to the schematic?

I can check your voltages against those in my radio if it's not too difficult to get at.

[gotham22]

Will get that to you this week.  Thank you for your help.  

[gotham22]

I think I may have figured this out. Appears to be a grounding issue. When properly grounded the voltage on the ic is close to the schematic. When not grounded properly it appears the ic is being over driven. More to come


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[hr369]

You're talking about grounding to the case?  Pin 9  counting from left to right is a ground also. Check that solder joint on that pin too.

Edited January 24, 2017 by hr369

[Dave WM]

make sure you have all the screws installed and tight when testing, some are used for grounding thru heat sinks. IIRC there are two screws on the back, you have to have at least one in making firm contact with the case.

Edited January 24, 2017 by Dave WM

[gotham22]

It looks like the screws were not full in and making contact with the case. When they are not making contact the audio amps (ha1339) are being overdriven with voltage. Once the do make contact all the pins on the chip return to their voltages as stated in the schematic. Looks like it is back in business!!! Changed a couple of diodes and the qc601 transistor as well.

On a personal note, thank you dave wm. I can't thank you enough for all of the responses and help you have given. You are what these forums are all about. Thank you


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[Dave WM]

I had the same problem, but mine manifested as intermittent sound, twisting the case would activate the amp portion. That's when I realized the screws were not installed.

Glad that was of help to you. Those sure are fun to work on eh? Like a puzzle getting them apart and then the constant fear of popping some wire loose and not knowing where it went.

[gotham22]

Fun is one word!  The good thing is I know a lot about radio repair now!  HA!  Broke many connections that I had to solder back and  I burnt a trace on the board which I needed to jump to fix.  Last issue I am tracking down is why I am only getting a signal on one speaker.  I tested the balance and I turned it both ways.  Only get one speaker outputting though.  I also made sure that the button with the "s" was set properly, think that switches between stereo and mono. I just got my hands on an oscilloscope to track the signal down.  

Once all that is figured out I am going back to the original project I wanted to do which was to add a switch to change power between the radio and aux input. Happy times are near!