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Old 4th Jun 2019, 7:59 pm   #1
nigelr2000
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Default Sharp VZ3000 no audio FM fault

I am doing battle with one of these upright music centres. Now I have done a lot of these units and never had a radio fault that didn't come down to dirty selectors but this one has got me confused, with no aerial a weak signal comes through ok but noisy, plug an aerial in and there is distorted audio either side of the tuning point but when tuned in the audio goes really low and no noise. Select stereo and theres is silence and no beacon light It has an HA11225 IF chip with an HA1196 stereo decoder, the front end is a FET with 3 transistors and a couple of filters at the end.

I don't have any experience on how this kind of setup works as I have never had to fault find one. I tried the easy way out and changed the IF chip but that had no effect.

Anyone got any ideas

snip of circuit enclosed
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Old 5th Jun 2019, 9:37 am   #2
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Default Re: Sharp VZ3000 no audio FM fault

Ooops forgot to press upload
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Old 5th Jun 2019, 10:38 am   #3
crackle
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Default Re: Sharp VZ3000 no audio FM fault

If it had been a conventional circuit with discrete components rather than IC's then I would be looking at changing the discriminator electrolytic cap.
But I can't see one in the diagram, neither can I in the data sheet for the IC. http://nice.kaze.com/av/HA11225.pdf
But then I hate IC's .

Mike
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Old 5th Jun 2019, 8:18 pm   #4
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Default Re: Sharp VZ3000 no audio FM fault

The datasheet linked to by Crackle has a useful section detailing the effect of components of less than and greater than the nominal values quoted in the test circuit. Have a look at the electrolytic capacitors C124 and C13x (I can't make it out, but it is connected to pin 12 of the IC via R131). They may be causing the mute circuit to misbehave.

Paula
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Old 7th Jun 2019, 1:45 pm   #5
Chris55000
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Default Re: Sharp VZ3000 no audio FM fault

Hi!

I'm a bit more used to that American style of typeface used on a lot of 1970s American and Japanese drawings and the capacitor on pin 12 is C135!

Have you tried carefully tweaking the "Mute Adjustment" preset VR101?

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Old 12th Jun 2019, 8:26 pm   #6
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Default Re: Sharp VZ3000 no audio FM fault

OK got it back on the bench today, tried the suggestions, no luck. the muting pot has no effect. I will have to do some voltage and scope work tomorrow as I have done the other 5 yes 5 of these nightmares, 2x 2500's 1x3000 and 1x3500 this is the only one left and then he can pick them up and free up some workshop space.
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Old 13th Jun 2019, 3:09 am   #7
tri-comp
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Default Re: Sharp VZ3000 no audio FM fault

The HA11225 should be easy to replace as it's equivalent with several others if the original is not available, see the attached NEC x-ref list.
Also attached is the NEC datasheet for uPC1167C2 which is their equivalent.
Moreover the full schematic for the VZ3000H Radio-section is attached.

Now, before thinking about replacing the chip I would check the Quadrature Detector Transformers T102/T103. More specifically the capacitors inside the transformers. They are known to drift causing misalignment of the FM-detector. Very likely this fault will show the symptoms described.
It will be fairly easy to determine if this problem exists. Notice the core-setting of each transformer and tune-in a station center with low volume level. Now tweak the cores either way around and notice if this restores sound. Possibly not to the full level, but at least an improvement.
If volume was improved the transformers are out of alignment because of failing internal capacitors.
First reset the cores to their original settings.
Now you should follow the alignment procedures as per the attached schematics pdf-file.
If you're unsuccessful in aligning the set reclaiming sound, I would suggest replacing the internal capacitors in T102/T103.
But, with WHAT ? The schematic doesn't show any values so this will be difficult.
Last time I had this problem in a Pioneer SX339 receiver, I took the transformer (only one in this recvr.) apart and measured the resonance of the transformer with a modified grid-dip-meter with output for a frequency counter for precise measurements. It was around 200KHz higher than 10,7MHz.
You can't trust this to be absolute accurate as the transformer-can is missing, but close enough. Then I removed the original cap. and measured it with a suitable capacitor tester. It was found to have some value around 100pF.
Normally the capacitor reduce in value when it fails but by how much ? At least the value you measure will give you a pointer. In this case I replaced it with 2 x 47pF in parallel and re-assembled the transformer. The missing capacity was added by mounting a small 30pF ceramic trimmer cap. across the appropriate transformer-legs, under the PCB. Now the FM-detector could be aligned as per instructions with the aid of the trimmer-cap.

Rgds,

/Torben
Attached Files
File Type: pdf VZ-3000_CP-V300H_Radio Section.pdf (138.9 KB, 88 views)
File Type: pdf uPC1167C2 x-ref HA11225.pdf (33.8 KB, 206 views)
File Type: pdf uPC1167C2.pdf (348.2 KB, 66 views)

Last edited by tri-comp; 13th Jun 2019 at 3:15 am.
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Old 13th Jun 2019, 1:21 pm   #8
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Default Re: Sharp VZ3000 no audio FM fault

I could kiss you Torben All sorted, I cheated and nicked T103 from a scrap board as it was simpler than taking it apart, I fitted it and got blasted out with perfect sound, I forgot to back the volume off before powered it lol.
That is certainly a fault I have not encountered before have a beer on me
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Old 13th Jun 2019, 3:50 pm   #9
tri-comp
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Default Re: Sharp VZ3000 no audio FM fault

I'm surprised you've never met this fault if you're repairing more or less vintage receivers. I believe it's quite common. Possibly not to the extent that all sound is lost as in your case. Distortion and lowered sound output on FM reception is more the rule. This problem has been described on lots of forums over time but I guess there's always a first

Glad you nailed it.

Rgds,

/Torben
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Old 13th Jun 2019, 4:01 pm   #10
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Default Re: Sharp VZ3000 no audio FM fault

I tend to repair more audio equipment and don't have much to do with RF fault finding unless I have to like in this case
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