Hi Guys,

I've decided to try and learn to repair the 72 model Hitachi Radio. KM-1520ZC however I cannot find this manual anywhere. I have 1 for TM-1081ZB(S) but not the 72 model radio.

The radio powers up, has static but doesn't tune into anything. I have so far managed to repair the tuner needle which wasn't moving when the knob was being turned. Think that is resolved now but next up I need to determine why it won't tune into anything.

Just stumbled across this guys videos and think it might be useful.

 

This is a worthwhile adventure. Slightly off-topic, but I think there have got to be some possible hacks, maybe substituting different transistors or power supply parts, that would improve the horrible power, sensitivity and selectivity of these radios. It's by far the quietest car radio I've ever heard, and my ghetto blaster picks up about twice as many stations. 

I was given this radio for nothing when I was visiting the US a year or so ago. Our AU market cars never had this radio, so I'm kind of using it as a guinea pig to see if I can repair it, before moving onto my TM-1081ZB(S) radio's. I've got 3 of those all working in terms of reception, but the auto-tune/signal seek function on 2 of them doesn't work in both directions and on 1 of them it's a little slow.

However I want to practice on a radio that isn't worth as much as the earlier AM radio. So far I've managed to fix the tuner needle which wasn't moving but have no idea what other tests I need to do to try and make it work. I figure the service manual is a good start.

At this stage how well it works or sounds is another matter.

maybe one of these sites or not. but hopefully get you in the right direction

http://www.manualsonline.com/

http://www.stereomanuals.com/

http://freeservicemanuals.info/en/?page=3&sort=typea&search=&sorttype=asc&brand=Pioneer

Antenna possibly bad connection or trimmer adjustment needed.  Hard to find schematic for the km-1520  below.

keywords hitachi radio schematic  km-1520zc schematic for future searches. km-1520 operation manual

Hitachi KM-1520ZC Operation Guide.pdf

schematic.pdf

Edited May 11, 20168 yr by hr369

Thanks I have seen Antenna trimmer written on the radio chassis before and had no idea what it was for.

A quick Google:

http://www.chevelles.com/radiotech/reception.html

Quote

 

TRIMMER ADJUSTMENTS 

On all factory radios there is a "trimmer" adjustment screw that is used to optimize AM reception by properly trimming the antenna (electronically). Normally this needs little or no adjustment, but when radio and antenna components get swapped or reception is constantly poor despite a normally operating radio, it may be necessary to use this adjustment. 

 

Sounds like it's worth a go. That schematic is also great. Although I really wish I paid more attention during Analog Electronics class back in my computer science degree days!

 I might add that trimmer is only for AM.  Also if you're inside a solidly built house, the reception might be bad.

Thanks but I somehow doubt that is the issue with this radio, mainly because the earlier AM radio's performed fine when I tested them (all 3). I will test it again now that I've fixed the tuner adjustment issue just to be sure. I did hear a crackle in the speaker so it should in theory be working with reception.

sure you have it hooked up right? 

Blue is + 

White  is speaker,

w/b is speaker and also ground

 

So.... the radio works sort of...

The Antenna trimmer screw seems to do nothing. Behind it is a wire that appears to be tensioned but really does nothing as far as I can tell.

The problem is the radio is half apart but.. I've had it working with loud clear volume and reasonable reception but moving the pieces of the radio around (it is still soldered to ground on the chassis in parts) so I can't remove it fully from it's chassis.

Near the blue power in cable is another brown and red wire to what looks like a small form of coil. I will need to take photos but the small wound coil appears to be part of the equation. The brown wire came undone and needs re-soldering but I was able to move the wire around on the solder point and find a sweet spot where the radio was clear and working correctly.

The coil doesn't look like an off the shelf part but I'm not that familiar with older electronics so maybe a modern replacement is available? Anyway I'll need to see what I can do. I'll take some photos of all the above, but basically it does work. Which I'm happy about but needs a few tweaks and a bit more troubleshooting.

The antenna trim screw probably adjusts the value of a small variable inductor of capacitor. I'm not sure if I'm understanding your findings or not, but there should be no visible physical mechanical change as you rotate the screw.

The other problem sounds simply like a broken connection. Is it something that you can't just resolder into place? Can you take some pics of the area of concern?

And as for off the shelf or not... Even if it was off the shelf in 1970, it's not off the shelf anymore. Things have changed.

Well then you found the problem. Solder it up if you can.  Now you found out why it was free   I looked at mine and couldn't find that coil you're talking about.

You could possibly talking about an IF transformer or just a transformer. 

A picture of the coil may help others that have the same problem.

My problem with these radio's is i  keep buying radios almost hoping someone sold me a dud and I can use it for

parts but every one works!  Im working  on one now that needs  just a volume/on off switch and I don't want to ruin a perfectly good radio

just for the switch.

 

 

 

 

Edited May 12, 20168 yr by hr369