Looking at the picture of the good output, the audio is between 6-8v. I assume that is normal?
I will start picking the crap glue out, and will try to desolder the caps to see if they are still holding their rated capacitance. My DMM can read caps, but not esr. What type of caps do you recommend they get replaced with?
What are the white parts that are near the caps? Fusibles?
I want a good radio cause no new radio fits in the radio slots of these cars. Mine will be going in my 1981 toyota tercel. The previous owner hacked up the wiring, and jammed a junk jvc radio in the hole. It looks real bad. The other reason is, a buddy of a buddy has a similar year toyota pickup, and wants it to maintain the original look as well. Only issue is, these old 2 post radios are getting real hard to find, especially in good condition.
They are Fujitsu MB3713's.
I’d probably use something like Nichicon VR series.
I have had a few Toyota’s here, oldest one was a ‘78 Hilux.
Good luck with the project.
I have had a few Toyota’s here, oldest one was a ‘78 Hilux.
Good luck with the project.
The speakers are AC coupled by large value cap connected between Pin1 and the speaker so 0VDC across the speaker and with no signal Pin1 should be at half supply voltage or close.
If a cap is dry it will usually measure lowered C, replacement standard decent quality will do.
No they are link/jumper wires can also be voltage test points.
A brake light globe in series with the 12V supply radios will diagnose power amp faults, replace chipamp and caps and you should be good to go.
IIRC these types of radio had RC or LC filtering for the radio section and the C may need replacing also.
Max.
Got the schematic, and we are in luck! The manual included I think both the japanese and us variants of the radio, which is for the celica. The japanese one is completely different, but the us variant is the same as the tercel radio.
Ill check the voltages the manual calls out for the amp. I still need to check the 2 black and 2 light green caps on each channel. I've been busy installing the motor on my car.
Anything else I should check now that we have the schematic? What are the large green things near the amps? Inductors?
Ill check the voltages the manual calls out for the amp. I still need to check the 2 black and 2 light green caps on each channel. I've been busy installing the motor on my car.
Anything else I should check now that we have the schematic? What are the large green things near the amps? Inductors?
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Power the radio up for a few seconds. If one output IC heats up much quicker than the other, either remove it or desolder it's B+ terminal.
Does the output heatsink heat up with that IC removed from the circuit?
Does the output heatsink heat up with that IC removed from the circuit?
I work 2nd shift, so I am unable to test things in the evenings when most people are online :/
The IC that works doesnt get very hot at all. The IC that makes loud popping gets hot quickly.
Are you wanting me to remove power from the bad IC and see if it still gets hot?
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I'm online at all times of the day because I rarely sleep for more than a couple of hours at a time.
I want you to take the dead IC out of the equation. There's no point is having to deal with that at this point.
I want you to take the dead IC out of the equation. There's no point is having to deal with that at this point.
Once I take it out, what do you want me to test for then?
edit: I suppose to test to see if the heat sink gets hot?
edit: I suppose to test to see if the heat sink gets hot?
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Yes you need to isolate abnormal loads such as blown chip amplifier ics.
It is most likely these amplifiers were 'killed' by too low impedance load or reverse polarity 12V....yes this happens surprisingly often.
Once faulty amplifiers are isolated you could connect say a headphone across the volume control and monitor the AM/FM stages.
Max.
So basically either using the radio with bad speakers or hooking up the battery backwards? Makes sense.
I know I've asked this, but I am wanting clarity on specifically what you want me to do. Do you want me to:
1. remove the IC and test for heat, or
2. remove IC, bend pin 2 out of the way, solder it back in, then check for heat?
I know I've asked this, but I am wanting clarity on specifically what you want me to do. Do you want me to:
1. remove the IC and test for heat, or
2. remove IC, bend pin 2 out of the way, solder it back in, then check for heat?
Yup.
You don't need to remove the chip amps, just isolate the jumper wires I have highlighted in red at A and B and check the operation of the radio section by connecting headphones across the volume control.
If all is good then proceed to diagnose which amplifiers are dead by connecting speakers and briefly reconnecting jumper at A OR B BUT with tail light parking bulb in series with the 12V supply.
Faulty amp will draw excessive supply current and cause the lamp to glow brightly even with volume control at mute, this is safe way to diagnose.
Max.
So shame on me for not following proper diagnosing advice and procedure. I have a couple spare MB3713's I ordered and replaced the one getting hot out of curiosity. Now, it doesn't get hot, plays audio at low levels, but as soon as you increase the volume from low to medium, the popping comes back. At low levels, I tried balance control and the tone control, and neither one did anything. I still need to pull the caps and check them in the output section. I shall dig around for a bulb and hook it up as a DBT to ensure it isnt drawing excessive current.
I know the FM radio circuit works, at least on the radio I've been working on. I've been using a BT-to-FM transmitter to transmit the 1khz test tone. The other radio with both channels dead doesnt do anything except get hot and the lights turn on. I'm saving that one for when I have a functional radio to use as an example.
Where would I connect my headphones to test the FM radio on the volume control? The wiper of each variable resistor? Also, would just the FM circuit have enough oomph to drive headphones?
Why do you think the balance and tone control dont work? More bad caps?
As for the popping, seeing as the amp is no longer getting hot, do you think its just one of the caps that has failed?
I know its all speculation, but I'm just trying to think what else could be causing these issues. Not knowing exactly what to look for and where makes it difficult for me to diagnose (hence why I'm here)
I know the FM radio circuit works, at least on the radio I've been working on. I've been using a BT-to-FM transmitter to transmit the 1khz test tone. The other radio with both channels dead doesnt do anything except get hot and the lights turn on. I'm saving that one for when I have a functional radio to use as an example.
Where would I connect my headphones to test the FM radio on the volume control? The wiper of each variable resistor? Also, would just the FM circuit have enough oomph to drive headphones?
Why do you think the balance and tone control dont work? More bad caps?
As for the popping, seeing as the amp is no longer getting hot, do you think its just one of the caps that has failed?
I know its all speculation, but I'm just trying to think what else could be causing these issues. Not knowing exactly what to look for and where makes it difficult for me to diagnose (hence why I'm here)
To be frank I am tired of you not following simple directions and lack of civil manners.
Connect a headphone driver or small PC amplifier/speakers across the volume control outer contacts, connect a suitable car antenna and you should have FM hiss or AM noise.
No balance control suggests loss of earth connection to bal pot, no tone control suggests loss of earth connection to tone pot which would be unusual, broken wires ?.
So, do you have line level audio between system ground and each of the two balance control outer pins (or vol control input pins, see schematic) ?.
Max.
Connect a headphone driver or small PC amplifier/speakers across the volume control outer contacts, connect a suitable car antenna and you should have FM hiss or AM noise.
No balance control suggests loss of earth connection to bal pot, no tone control suggests loss of earth connection to tone pot which would be unusual, broken wires ?.
So, do you have line level audio between system ground and each of the two balance control outer pins (or vol control input pins, see schematic) ?.
Max.
What civil manners am I lacking? I understand the not following the procedures, but its not like I'm going around calling people names or belching in your face...
I don't have a headphone driver or small pc speakers to work with. In your earlier post, you said to connect headphones across the volume pot, not a headphone amp. As I mentioned before, the radio I am currently working on has a working FM circuit. No testing is needed on it, and I do not care about AM. As for the second radio, there may be an issue with the radio circuit, or the AM FM switch may be dirty seeing as the power button didn't work until I cleaned it.
I will check the balance and tone control later once we have a functional radio. It might be because I have all the screws taken out of it to work on the amp, and it lost its ground due to that. Or it might be a broken wire or another bad electrolyic cap. If thats the case, its going to be a huge pain to get the controls out due to how they are hooked into the radio chassis.
We already know the FM signal is getting to both IC's as confirmed with a scope. The first issue was that the dead channel's IC was getting hot and was producing loud popping noises. Yes, I should have used a DBT to ensure no damage was done to the radio, and to see if there was a short somewhere. Shame on me. I replaced the chip IC and it no longer got hot, indicating that the bad IC had an internal failure. However, the popping is still present.
I went ahead and pulled the light green capacitors and the dark green one as it causes no harm to anything to check them, and just about everyone who has commented said they need to get replaced. I pulled one of the four 1000uF caps, only to find out my DMM can only test up to 200uF. Here are the values my meter gave me. Factory will be in (). I think you'll see the issue:
C86 155nF (.15uF)
C80 35nF (47uF)
C78 124uF (100uF)
C85 152nF (.15uF)
C79 64uF (47uF)
C77 138uF (100uF)
Now, I don't know if its my meter, or if the values have drifted that much. But look at C80. It is no where near the original value, and it was gradually getting lower the longer I held my meter on it. My guess is with the cap between pin 1 and pin 3, it's fine at a super low voltage, and as soon as it starts to charge, it shorts and sends voltage directly to the speaker and to the output of the amp, hence the popping. I might have damaged the amp IC I installed because of this. Either way, I am going to order new caps for the amp section, then we can go from there diagnosing tone control and balance, then the second radio.
C80 is in the foreground, and C79 in the background. It's hard to see but the bottom of C80 is bulging out.
I don't have a headphone driver or small pc speakers to work with. In your earlier post, you said to connect headphones across the volume pot, not a headphone amp. As I mentioned before, the radio I am currently working on has a working FM circuit. No testing is needed on it, and I do not care about AM. As for the second radio, there may be an issue with the radio circuit, or the AM FM switch may be dirty seeing as the power button didn't work until I cleaned it.
I will check the balance and tone control later once we have a functional radio. It might be because I have all the screws taken out of it to work on the amp, and it lost its ground due to that. Or it might be a broken wire or another bad electrolyic cap. If thats the case, its going to be a huge pain to get the controls out due to how they are hooked into the radio chassis.
We already know the FM signal is getting to both IC's as confirmed with a scope. The first issue was that the dead channel's IC was getting hot and was producing loud popping noises. Yes, I should have used a DBT to ensure no damage was done to the radio, and to see if there was a short somewhere. Shame on me. I replaced the chip IC and it no longer got hot, indicating that the bad IC had an internal failure. However, the popping is still present.
I went ahead and pulled the light green capacitors and the dark green one as it causes no harm to anything to check them, and just about everyone who has commented said they need to get replaced. I pulled one of the four 1000uF caps, only to find out my DMM can only test up to 200uF. Here are the values my meter gave me. Factory will be in (). I think you'll see the issue:
C86 155nF (.15uF)
C80 35nF (47uF)
C78 124uF (100uF)
C85 152nF (.15uF)
C79 64uF (47uF)
C77 138uF (100uF)
Now, I don't know if its my meter, or if the values have drifted that much. But look at C80. It is no where near the original value, and it was gradually getting lower the longer I held my meter on it. My guess is with the cap between pin 1 and pin 3, it's fine at a super low voltage, and as soon as it starts to charge, it shorts and sends voltage directly to the speaker and to the output of the amp, hence the popping. I might have damaged the amp IC I installed because of this. Either way, I am going to order new caps for the amp section, then we can go from there diagnosing tone control and balance, then the second radio.
C80 is in the foreground, and C79 in the background. It's hard to see but the bottom of C80 is bulging out.
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Where I'm from it's customary to give acknowledgment and thanks, and using a real name too, perhaps I'm old school it's called respect.
I first suggested headphone driver because they are sensitive and you will hear something and I supposed you would have some suitable.
I advised this step because I didn't trust that the radio is working, and now you mention that earth screws are out, the first thing to understand in car audio is that pcb/screw earths matter.
Earth screw ?.
Electros of the day had -20%>+100% tolerance range and they were mostly over value so any under value are immediately suspect, especially aged caps with small diameter cans, the rubber bungs don't seal so well long term as larger diameter cap sizes.
That C80 is what's called a bootstrap cap and is critical to operation of the amp, the one you have is essentially open circuit and will cause low gain and distortion.
Like I said in my first post replace the small caps first as a matter of course and use a bulb tester to diagnose chip amps condition.
My apologies. I usually wait until I / we / you figure out what the issue is before giving thanks. I do appreciate the help you are giving me, Max Planck.
No worries. I'm not an audiophile, so I don't have a dedicated headphone driver, and the speaker setup I'm using with my computer is a dell branded ada995 altec lansing 5.1 surround sound system. I am definitely not hooking a sketchy radio up to that.
I do understand this. I have a jumper between the amp board and the rest of the radio. Without it, the radio wont work. Once I replace the caps, if the tone and balance controls still arent working, I will make a new forum post about it instead of continuing this one.
I will replace the caps and go from there. I will definitely want to make the tester for the other radio, but that'll be in a different forum post.
Good then Mr Noname.
I mean any old headphones/ear buds and two alligator clips, one connecting HP plug sleeve to radio chassis and the other connecting HP tip to circuit points.
You will get programme in one ear only but this HP tester is a sensitive and useful quick 'listen in' on the audio path, you can connect the 'active' alligator clip to a small screwdriver and use as a probe.
You can do the same with small cheap PC speakers input plug and have more sensitive probe that does not cause loading.
Yes, new caps and a BT and you should be good to go but make sure of ALL earth connections.
I say keep it on this thread as part of your voyage of discovery as it were.
Same deal, I say keep it on this thread as follow on project.
BTW I have professionally repaired for 40 years, I am trying to keep this simple and easy as this kind of fault should be provided directions are followed.
I understand wanting to keep factory look and these were good sounding and sensitive radios in their day and also feature ferrite tuning gang, now extinct as a tuner circuit technique.
With some simple mods it would be easy to sacrifice AM or FM function and insert audio signal from a phone/player or BT receiver etc, I can talk you through this if you want.
Max.