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.

 

Sorry for the late reply on this, I've been quite busy lately. The short of it is, the radio works. But interestingly I have noticed that sometimes I don't get great reception unless I put the negative lead near to the ground wires on the radio chassis.

Here is the strange thing. Say I tune the radio in to a certain frequency and I'm getting clear transmission. I switch the radio off, leave it say until morning. Go back and reconnect it to power the radio powers up but the reception is gone. If I move the black negative lead close and around the grounded black wire on the chassis (there is a couple of spots) suddenly reception comes good?

I've attached photos of the transistor / coil thing I was talking about, you can see the brown wire is not soldered down. I've now soldered it in place and the radio works, apart from the somewhat strange behavior when it comes to moving the negative terminal on my 12V supply around on the chassis with relation to reception.

The radio is not back together so half the chassis is not back together which may explain this odd behavior, however before I can reassemble I'm having some trouble putting it back together. I should have taken more photos but the transistor part I'm not sure where to fasten it down. Does anyone have photos of the internals of the radio so I can see how everything is orientated?

This rear left area of the radio I can't remember how to attach the remaining components, if anyone has photos of how this should be organised please do share. I can take better photos later of the trouble spots.

Radio lights up and works..has reception etc..

Where the dodgy solder point was, brown wire on this terminal post bit... I've since soldered it.

Transistor?

sounds like an intermittent connection at the transformer. Not sure what kind of transformer it its, but has to be audio, so its prob an interstage coupling transformer or maybe even an audio out (I would have assumed it was capacitor coupled but being that old and low power it could be audio out). the typical process would be to ohm check the transformer out of circuit if it looks suspicious. Or you could signal trace it to see where the signal is dropping out when its not working.

My guess is moving the wires around is simply uncovering a crack in the trace of the board OR intermittent wiring. I have an old 8 track AM/FM that I may pull out and service, it works but the tone control  seems bad, could be a break in the resistance trace or just dirty. While I have it out I plan to replace the electrolytic caps as they are way past normal service life. Working on vintage electronics requires very gentle handling, as the wires and PCB are old and hardened up, making them easy to crack. One thing you don't want to do is mess with any of the tuning of the IF transformers, we call that screwdriver drift, the tuning of the IF will be ok unless its been messed with.

if you are interested in transistor radio repair, check out Shango066 on you tube, he has a lot of videos, no car radio stuff but plenty of transistor radio.

 

Edited May 30, 20168 yr by Dave WM

I'm away from home and have spotty internet access, so I can't go into much detail, but I'll do what I can.

The device you are calling a "transistor?" is a coil or transformer of some sort. Hard to tell from the pics, but it looks like it only has two wires going to it, and if I remember correctly, the whole radio goes dead when it's not connected? If that's the case, it's probably what they call a "choke" and it's purpose is to filter out high frequencies on the power input line so the noise doesn't affect the electronics inside the chassis.

If it is a choke on the incoming power, it exists to keep noise from the ignition coil from messing with the radio.

Also the terminal block thingie looks to me to be a line of "feed thru capacitors" who are another means to filter signals. One feed thru for each wire entering or leaving the device. Can you take a pic of the other side of that block?

Of course I'm looking on a tiny dark screen and am guessing...

As for how stuff fits back in, my experience is that kind of equipment is so tightly packed that stuff only fits one way! Think Jenga or Tetris.

oh I see the schematic now, yes looks like it could be the choke, will need better pics of where it was on the board. Feed thru caps can develop shorts. I see it is cap coupled. I would be tempted to at least check that 470uf cap if the audio lack bass.

When you get it working I can tell you how to operate it.

 

Here are some pics of the inside of my 1520ZC.  That is the model you are working on right? Your's looks completely different.

Yep odd......internally mine looks very different. I wonder if there was more than 1 model with the same faceplate?

looks like a hitachi from another datsun that they put a 240z faceplate on. Doesn't even have the mount for the antenna switch on top of the case.

Edited June 1, 20168 yr by hr369

That's what I was thinking also, sadly...

1 minute ago, Gav240z said:

That's what I was thinking also, sadly...

You can use it for parts. Volume switch looks similar and the AM FM pushbutton knobs are probably the same.

Edited June 1, 20168 yr by hr369

True, but I hate to sacrifice a somewhat working unit.. We shall see what it's fate is.. :).

Regarding the poor reception of these AM radios, I just got hold of a TM-1081ZB and its sensitivity is zilch.  I've noted that on other series 1 radios that the sensitivity was pretty poor also but

my latest one is dead. So, I started by replacing one of the RF transistors and got to thinking this radio will need an alignment after replacing any of the RF transistors and I don't have

a signal generator to align it. So, I found the guru of AM radio repair on youtube and just sent him my radio for repair. I asked him to please video the repair process because this is

a pretty common problem on these old signal seekers.  I will post a link to the video on here when he uploads it.  So if any of you guys like to tinker on these radios, this may help you

in troubleshooting what's wrong and you might be able to repair yours for the cost of a transistor.  This should also apply to any first gen s30 hitachi am/fm. The only difference it

appears  is the location of the transistors on the boards. Stay tuned.

 

 

Edited July 4, 20168 yr by hr369