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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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1st Jan 2021, 5:37 pm | #1 |
Triode
Join Date: Jan 2021
Location: Buckingham, Buckinghamshire, UK
Posts: 17
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Hitachi KH-1190E portable radio
My Hitachi KH-1190E portable radio (mains and battery) - stopped producing any sound a few days ago whilst in use on mains. I have checked the voltage going into the PCB when on battery and its around 5.8v. (it takes 4 D cells). I can't see any obvious bulging capacitors or anything else burnt out. I have taken a photo of the PCB and also attached a schematic of it.
I have tried an ear plug in it and just get some very soft white noise. Has anyone any ideas on likely components to go wrong or a method of testing please? Thank you |
1st Jan 2021, 6:32 pm | #2 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,482
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Re: Hitachi KH-1190E portable radio
Hello Mart, Happy new year and welcome to the forum.
As a general rule on radios like this the radio section is before the volume control and the audio amplifier section is after the volume control. Checking with a headphone was a sensible first step to rule out failure of the speaker. Next thing, with the headphone unplugged, power on, volume wound up quite high, try touching the volume control terminal I have indicated on the attached image either with your fingertip or ideally with the tip of a terminal driver with your fingers touching the metal shaft. If you don't hear anything, try touching the next terminal up on the volume control (the middle one). If the amplifier section is working you should hear a loud buzz from the speaker when you do that. Please do -not- go touching the same screwdriver to anything else in the set, especially in the power supply area. Sorry to sound overcautious but as you are new to us, we don't really know what level to pitch our advice at. The audio amplifier is an interesting design as it appears to use two TBA810 power amplifiers in a 'bridge' configuration for higher mono output power. Probably sounds quite beefy when it's working. |
1st Jan 2021, 9:14 pm | #3 | |
Heptode
Join Date: Jan 2009
Location: West Lothian, UK.
Posts: 760
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Re: Hitachi KH-1190E portable radio
Quote:
Is the PCB voltage similar when switched to mains? The circuit was reduced a bit too much for me to read details. They sometimes survive the forum upload procedure better as a PDF if you can do that.
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George |
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1st Jan 2021, 10:13 pm | #4 |
Triode
Join Date: Jan 2021
Location: Buckingham, Buckinghamshire, UK
Posts: 17
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Re: Hitachi KH-1190E portable radio
Thanks very much for your reply and Happy New Year.
I tried touching the volume control connection with a screwdriver (whilst touching the metal on it). There was no buzzing on either connection. No that’s fine stating about the dangers of touching the power supply etc. Thanks |
1st Jan 2021, 10:19 pm | #5 |
Triode
Join Date: Jan 2021
Location: Buckingham, Buckinghamshire, UK
Posts: 17
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Re: Hitachi KH-1190E portable radio
Thanks for your reply. The noise seems the same on mains.it’s not very loud on either.
The voltage on pcb is higher on mains about 7.57v. Thank you |
1st Jan 2021, 10:20 pm | #6 |
Triode
Join Date: Jan 2021
Location: Buckingham, Buckinghamshire, UK
Posts: 17
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Re: Hitachi KH-1190E portable radio
I tried uploading as a pdf but I think the file size was too big just over 4mb.
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1st Jan 2021, 10:45 pm | #7 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,482
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Re: Hitachi KH-1190E portable radio
OK Mart, that preliminary result suggests there could be a problem with the audio amplifier section. Since you have a meter, can you look for power to the two audio amplifier ICs?
Check for a supply voltage on pin 1 of both of the audio power amplifier ICs (see attached IC pinout). I know you said you had ~6VDC going to the PCB, this is to check that it is reaching the amplifier ICs. Try attaching the original diagram scan in a .zip file - as long as the size of that file does not exceed the allowed size for a .zip that should work. |
2nd Jan 2021, 12:43 pm | #8 |
Triode
Join Date: Jan 2021
Location: Buckingham, Buckinghamshire, UK
Posts: 17
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The two ICs have 0v on their power in pins.
I have reattached a compressed version of the pdf. Correction approx 5v at both pins when I use the ground on the ic. I was using the negative on power into pcb before. Tried again with negative into pcb and now getting 5v on both ICs I think I just had a bad connection before. |
3rd Jan 2021, 3:20 pm | #9 |
Heptode
Join Date: Jan 2009
Location: West Lothian, UK.
Posts: 760
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Re: Hitachi KH-1190E portable radio
The pdf circuit is much clearer (especially with the split pages).
I am not familiar with the radio but notice that the output from the detectors (both AM and FM) TP3 and TP4 are fed to Q10 then the volume control. In the path to Q10 there is a changeover switch operated by the DIN connector so this is a possible place to lose all the audio signal. Pin 5/3 of the DIN would be a handy place to inject an audio signal from CD/MP3 etc to check the audio amplifier(s).
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George |
3rd Jan 2021, 3:26 pm | #10 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
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Re: Hitachi KH-1190E portable radio
On the back of Buggies's observation you could also just try plugging / unplugging a suitable DIN plug a few times as it may just be that the switch in the socket is dirty - that might show up if you 'exercise' it a bit.
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3rd Jan 2021, 9:56 pm | #11 |
Triode
Join Date: Jan 2021
Location: Buckingham, Buckinghamshire, UK
Posts: 17
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Re: Hitachi KH-1190E portable radio
Not having much luck. I haven't got a DIN plug - so tried putting wires into the socket but got nothing out of speaker. I guess I have to push the plastic pin it at the top at the same time but that is tricky. I did exercise the sprung metal at the back of the socket to see if that would help - but it didn't. Also wasn't sure which are pins 3 and 5 of the socket.
I did get sound out of the speaker if I connected the sound lead (connected to hifi radio) across pins 1 and 3 on the volume control. (where 1 is the lower connection of the three on the right). |
7th Jan 2021, 4:16 pm | #12 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
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Re: Hitachi KH-1190E portable radio
OK, well your amplifier section is obviously OK. (Strange that the 'buzz test' did not work, but injecting an audio signal as you did is a better, more hi tech way of doing the same thing).
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7th Jan 2021, 5:10 pm | #13 |
Triode
Join Date: Jan 2021
Location: Buckingham, Buckinghamshire, UK
Posts: 17
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Re: Hitachi KH-1190E portable radio
I am waiting for a DIN lead to arrive to see if this works as well to confirm the amplifier is working properly.
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9th Jan 2021, 1:21 pm | #14 |
Triode
Join Date: Jan 2021
Location: Buckingham, Buckinghamshire, UK
Posts: 17
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Re: Hitachi KH-1190E portable radio
Tested with DIN lead plugged into stereo - it works but not very loud have to turn the stereo right up and the radio. Its also distorted.
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9th Jan 2021, 1:26 pm | #15 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,482
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Re: Hitachi KH-1190E portable radio
Sorry, it's not clear if you are connecting speaker outputs from your source to the DIN socket, which will be expecting line-level inputs.
You may very well get distortion and other effects if you do that. Ideally take the source audio from the source system's TAPE OUT sockets if it has one, or use the phono / RCA jack output from a hi-fi 'separate' (like a CD player, tuner or cassette deck) as the source. |
9th Jan 2021, 7:42 pm | #16 |
Triode
Join Date: Jan 2021
Location: Buckingham, Buckinghamshire, UK
Posts: 17
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Re: Hitachi KH-1190E portable radio
I used the headphone socket on the tuner to connect to the radio DIN socket. Should this work ok?
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20th Jan 2021, 9:29 pm | #17 |
Triode
Join Date: Jan 2021
Location: Buckingham, Buckinghamshire, UK
Posts: 17
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Re: Hitachi KH-1190E portable radio
I have found R37 a 150ohm resistor is open will try replacing that to see if fixes it.
However during testing I broke D3 a 1N60 diode. I notice there are germanium and Schottky diodes with the same part number - does it matter which is used. Its a clear glass diode with black blue black bands on it. Thanks |