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Old 3rd Aug 2021, 9:34 am   #1
lightning
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Default Hitachi portable radio

l've recently bought a 1970's Hitachi three band radio, it's a pretty standard unit for the time.

lt's in good condition and works well on LW and FM.
However, on MW it's fine at the top end of the band but from about 1200Khz there's absolutely nothing.

Can anybody give me any pointers as to what the fault might be? lnside looks untouched, as in nobody has messed with the IF transformers.

l've had a radio where these had been disturbed and the set didn't work properly, once re aligned (by someone on this forum who l sent it to) it worked fine.

Would it be worth replacing all the electrolytic capacitors?
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Old 3rd Aug 2021, 9:48 am   #2
Nuvistor
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Default Re: Hitachi portable radio

No don’t replace any components until you have done some fault finding, confirm the LO osc is working at the part of MW that there are no stations is a reasonable first step.

Have you any test equipment to start fault finding?
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Old 3rd Aug 2021, 11:28 am   #3
lightning
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Default Re: Hitachi portable radio

Well, l've just acquired an oscilloscope. Not sure it will do me any good though, last time l used one was about thirty years ago!

Best start reading the manual. This radio will be good practice.
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Old 3rd Aug 2021, 11:59 am   #4
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Default Re: Hitachi portable radio

A model number for the Hitachi would help to narrow down the problem area and help others to advise possible solutions.

Dave
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Old 4th Aug 2021, 8:46 am   #5
lightning
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Default Re: Hitachi portable radio

It's a Hitachi KH-1015L

MW has gone off completely now
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Old 4th Aug 2021, 12:15 pm   #6
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Default Re: Hitachi portable radio

I assume you've already cleaned the wavechange switch contacts?
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Old 4th Aug 2021, 12:27 pm   #7
G6ONEDave
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Default Re: Hitachi portable radio

There don't appear to be any semiconductors solely involved with MW, Q6 is used for both MW & LW. Check that the band switch is making proper connections through it's contacts Sf3, Sa3, Sb3, Sh3, Si3 and Sj3. Other areas to check are coils L6 & L8, also their associated capacitors being C31, TC5, C34, C36, C37 and TC6 as well as R25. There is the possibility that the preset trimmer capacitors TC5 and TC6 on the poly variable tuning capacitor have failed. Don't disturb them unless you really have exhausted all other possible causes, as these presets are very easily damaged and a replacement trimmer or replacement poly tuning capacitor are becoming rather difficult to obtain. Sorry got a mental block on the proper name for the poly type capacitor, hopefully another member will provide that.

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Old 4th Aug 2021, 9:13 pm   #8
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Default Re: Hitachi portable radio

Thank you for the comprehensive advice.
l bought the radio because l saved up and bought one as a kid.

The wave change switch was a bit dodgy but after a spray with Servisol
it seems to be OK

Funny enough l touched the top of the tuner with my screwdriver (didn't adjust anything) and that's when MW went off completely.

l've seen another of these radios for sale at £10 so l may buy it and make one good set from the two.
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Old 5th Aug 2021, 10:37 am   #9
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Default Re: Hitachi portable radio

Well that confirms the bad news, you have at least one faulty trimmer cap on the main tuner variable capacitor. The problem with buying a second set to get one working is that it needs to be fully working on all 3 bands, or you may get the same problem.

It is possible to replace the faulty trimmer capacitor but you need lots of patience and a steady hand. You will also need a suitable preset capacitor as a replacement. I did this on a Roberts radio recently. The trimmer will be about 22pf and ideally of ceramic construction and very small in size. I could tell you the method that I used if it would be of help.

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Old 5th Aug 2021, 8:32 pm   #10
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Default Re: Hitachi portable radio

l've bought the second set which is said to be fully working so will see what it's like when it arrives.
lf it's good, l will attempt repair of my existing set.
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