Hitachi KH-1190E radio stopped working

[Martfoxy]

My Hitachi KH-1190E was being used on mains but stopped working - no sound. I have tested on battery but still doesn't work. I checked the input voltage to the pcb and are getting around 6V (4 of 1.5D cells).I have checked voltages on three transistors:

Q8 B 0.32v C 0.65 and E 0 should be B 1.3v C 2.78 E 0.72
Q9 B 0.5v C 0.62 and E 0 should be B 0.6v C 2.85
Q10 B 0.54 C 0.60 and E 0 should be B 0.7v C 2.47 E0.1

Can anyone help on this please? I have attached schematics.

 

[Bluejets]

Haven't recently plugged an earphone in at all...??

 

[Martfoxy]

No not before it stopped working. I did try afterwards but only got a very soft white noise on earphones.

 

[73's de Edd]

Both AM and FM are missing of any sound ?
What is the voltage at both pin 1's of IC1 and IC2
Also the voltage reading across zener D5 ?

 

[Martfoxy]

Yes both AM and FM are missing sound.
Both pin 1s are 5.6v
its 0.22v one way and 0v the other.

 

[Martfoxy]

Correction 0.22v both ways.

 

[73's de Edd]

Sir Martfoxy . . . . .

O.K., then it looks like that the audio power output ic's are not bad and thereby not bleeding down the derived SUB power supply line of its needed voltage.
So the . . .4.7 VDC . . . D5 zener regulating diode now smells most suspect.
And if they are cramped for space, I am suspecting that diode has one lead folded up beside its body and that they are mounting it vertically.
And in my seeing that the downstream transistors, sharing that developed sub supply, have 220 or 1k isolative resistors as collector series dropping resistors.
I don't suspect any shorted out transistor junctions . ..just yet.
Lets put the positional plane of the radio, with end solder joints of D5 facing towards the ceiling and then unsolder that D5 by adding two big BB sized drops of new solder to its present two leads being soldered points to the pcb foil.

Eyeball WHICH diode lead is WHICH now, for future install reference.

Then the diode should pull out the bottom with ease, after a slanting soldering iron tip liquifies BOTH of those BB laden solder joints simultaneously.
Then test the diode ohmmically to see if it doesnt read of a very low ohms reading , by using both polarity possibilities of your ohmmeters test leads.
If so, you are being in the market for a new 4.7 V zener diode, but if you are looking forward to a 100 year reliability factor of the new, one replace that present ~500mw unit with a 1 watt unit like a 1N4732 or 1N4732A or 1N4732B.

Now if you are still being left uncertain of / in ¿ ¿ ¿ ¿ your testing ? ? ? ? . . . . . . of the D5 unit . . . . .jes call me at BR549 . . . . . and ma will run out and fetch me up frum the mule barn . . . .and we can then further discuss yore conundrum in an even greater perspective and depth .



Thaaaaaaaaaaaaassit . . . . .



73's de Edd . . . . .



Budget:
A specialized systemology for going broke . . . . . . . BUT . . . . . . by doing it methodically.



.

 

[Martfoxy]

Thanks for your detailed reply.
I have taken D5 out and as far as I can tell its open both ways. I also took out the large capacitor C29 to test for shorting but seems ok.
I measured the resistance across the pads on the pcb and measured 7 Ohms.

 

[Bluejets]

Thanks for your detailed reply.
I have taken D5 out and as far as I can tell its open both ways. I also took out the large capacitor C29 to test for shorting but seems ok.
I measured the resistance across the pads on the pcb and measured 7 Ohms.

What are you using to test components..?
I found the little component tester off Ebay etc. for around $30.00 to be invaluable especially with a range of different components.

 

[Martfoxy]

I am using a Maplin Precision Gold WG020 meter.
I have tested the zenor diode on diode test get 0.72v

 

[73's de Edd]

That zener should be good then . . . . if you want to positiely nail it, just DC voltage monitor it while you use a 9V rectangular "radio" battery to feed its + terminal to a 1K resistor that has its other lead end going to the diodes cathode . . .banded end . . . . . of that zener.
The meter neg then goes to anode of the zener and the neg of the battery.
HOWEVER . . .. the REAL suspect/ cause is the 7 ohm loading of that sub voltage supply line to ground.
The E-cap was a good suspect . . . and any others . . .as all o the other caps endikig up from that buss to ground are being commonly "infallible" other types.
And that just may be a real hassle in isolating parts, if the foil path circuitry is being as dense as small pocket transistor radios are.

 

[Martfoxy]

That zener should be good then . . . . if you want to positiely nail it, just DC voltage monitor it while you use a 9V rectangular "radio" battery to feed its + terminal to a 1K resistor that has its other lead end going to the diodes cathode . . .banded end . . . . . of that zener.
The meter neg then goes to anode of the zener and the neg of the battery.
HOWEVER . . .. the REAL suspect/ cause is the 7 ohm loading of that sub voltage supply line to ground.
The E-cap was a good suspect . . . and any others . . .as all o the other caps endikig up from that buss to ground are being commonly "infallible" other types.
And that just may be a real hassle in isolating parts, if the foil path circuitry is being as dense as small pocket transistor radios are.

 

[Martfoxy]

Thank you very much for all your help. I will keep looking at this radio when I have some spare time and if I find out what is wrong will post solution - might be very difficult to fix though as there are so many circuits connected to that secondary power line and no easy way to isolate each one apart from desoldering components.

 

[Martfoxy]

I found a 150 Ohm resistor that is open R37. So ordered another one. Will see if that fixes it.

I did break a small clear diode D3 - its got black blue black bands on it. What type would I need to find to replace it with?

Thanks

 

[bertus]

Hello,

On the top right corner this is given on page 3 of the given document for D3:

It seems to be an 1N60.

Bertus

 

[Martfoxy]

Thanks I didn't notice that!

 

[73's de Edd]

Martfoxy . . . . .

Well its like this . . . . if you will track the main 6V HEAVY supply line buss that was feeding the IC1 and 2's pin 1's . . . on across the page . . . . and aross the gap in the page ! ! ! until it meets with the "same ? " HEAVY buss that runs both up and down. Use the top path HEAVY buss routing and it will join with your " opened" R37 150 ohm which is being responsible / functioning for supplying that top HEAVY buss that then runs BOTH right and left and has your
( assuredly good ) D5 ZENER regulating diode across it on the path going to the right .. . . . so . . . . that thereby opened supply circuit path should be your ACTUAL problem.
If you even heard anything it must have been from minute voltage bleed around a possible sneak path to this buss.
That voltage supply level is then being reduced to yet a sub- sub voltage level thru the R18 resistor and its conjunct C45 filtering E-cap.
As for your broken D3 diode, its function is being as a FM peak limiter and the units FM should work without it until you get a / its proper replacement.

( Pee Ess . . . . . did you pay enny uf yer hard earn-ded-ded munneys for this substandard schematic ?) ( It's split into two parts, with no overlapping / replications of the schemas mid sections / gaps parts and the left half is only being 90% sized.) And of course, the smaller tandem photo has resolution / definition / pixelation limitations.

73's de Edd . . . . .

Typically . . . . . parents will have to spend three years, in their fully teaching their kids to talk, and then spend the rest of their lives trying to get them to keep quiet.


.

 

[Martfoxy]

Yes I see the resistor on the schematic (I agree the schematic is poor quality - luckily it was cheap - it confuses me trying to follow the lines from one side to the other! - still better than nothing maybe I will try another supplier).
I haven't tested the voltage on D5 yet - is that important - what problems would it cause if not correct?
Ok will take your advice on the diode D3 - I ordered a 1n60 from ebay - says its germanium but I have read lots of messages saying its not and is a schottky diode - I think the proper germanium ones are rare - does this matter - I want it to work as well as possible.

Also noticed C42 is missing/snapped off - maybe in the past. What problems would this cause?

Thanks

 

[Martfoxy]

I received the diodes which are supposed to be germanium to replace 1n60 (D3)- can you tell from the photo attached?
I measured it on the diode tester and it reads 0.290. Thanks.

 

[bertus]

Hello,

The 0.290 will be correct as the 1N60 is a germanium diode.

Bertus