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Technics SU-V1X - No sound, Voltage on speaker terminal

AN7062. Is pin 1 continuous to ground?

Try shorting pin 2 and 17 to ground. What output voltage is there when 2 and 17 are to ground?

Power IC SVI2003A is fine - no faults there.
 
Hi,

pin 1 is continuous to ground.

When pins 2 and 17 are both shorted to ground they both measure 0 V, as does pin 1.

Also before I have done that a spark went while measuring and now collector of q505 is +3 V. (before it was either positive 44 or negative 44)
 
Having said that... BEWARE OF EBAY FAKES... sad fact that this ic has been counterfeited. A known original will have the triskelion logo (3 triangles on 1)

The counterfeit ones are harder to see the part info and have the M in a square.
 
Hi,

Voltages on speaker terminals are right 21, left 18.
voltages on pins 1,2 and 17 are 31 V.

So I am going to look for an7062.

For my own understanding, could you please elaborate how the shorting the pins and the transistor should bring the voltages to 0 if an7062 was ok?

Many thanks for your help, really appreciated.
 
Pins 2 and 17 of AN7062 (inputs) to ground should result in 0V at output of amplifier.

Bridge of collector/emitter on Q505 will un mute AN7062 and apply CURRENT STABILISER voltage to SVI2003A

If voltage out is not 0V issue is in voltage amp (differential/cascade) in AN7062

I would recommend also putting in 2 new 2SA1123 pre drive transistors- as you mentioned a short happening there, to be safe from transistor failure it's best to change them.
 
Thanks very much for the explanation. I can't find an7062 with the triangle logo anywhere, only with M logo. Would the 'fakes' still work?

I will get the transistors too.

Petr
 
not in the amps I put them into.... had an amp with 100mV DC offset.... put one of the new chips in... it just went up in smoke.... so did a 2nd.... pulled one from another amp, it worked perfectly.
 
Hi, just a quick update and quick question. I got another working unit to be able to do direct comparisons. I have swapped the an7062s and the good amp actually works with an7062 from the bad amp. Bad amp still had high voltages on pins that should have 0 or low voltage. Then I swapped the SVI2003A. The good amp still works, but the sound is distorted and some voltages are incorrect, so the SVI2003A is faulty. The bad amp with both good ICs still have wrong voltages. So there must be something else wrong, I will test it component by component.
Question - can I use svi2003 as substitute for svi2003A? I can't find svi2003A anywhere, I can find svi2003.
Thanks
Petr
 
Hi, another update. I now have the bad amp with good ICs. I have tested everything in sections 400 and 500. I have discovered that Q402 was opened, so I swapped both q401 and q402 from the good amp. I then had negative voltages in the muting circuitry, found out q502 was open. Got the working part from the good amp. I still have positive 30 V on speaker terminals. I have used the tone board from the bad amp in the good one previously and it worked fine so tone board should be ok, I know my ICs are good and I think I have checked all resistors,diodes and transistor in the power amp and mute circuit. Electrolytics are new. There is somewhere where the 30V DC is leaking into the signal path, but I can't figure out where from:-) I am basically where I started as far as voltages go. Collector of 505 is sometimes correct -40something, sometimes positive. Pin 18 on 7062 though is always positive 26, instead of negative 10.
On SVI2003A, pins 2,15 and 4,13 bring the correct 40+ positive and negative voltage. Pins 8 and 9 are correct 0, 7 and 10 are correct -14 V.
The rest that should be 0 or +/- 1.8 V are 32 - 35 positive.
Any idea, or any suggestion as to what to check?
Also what would be a good substitute for the q401 and 402 - original part 2SA1123?
And q502 - 2SCI685NC?
Thanks
Petr
 
It's fixed!! After the last time when I found open resistor and 2 transistors but still had the wrong voltages I got to it today. I checked again if pin 1 on 7062 is continuous to ground and it was, when I had the unit flat, wasn't when it was on its side. Checking wires and connections, then I discovered, that it was connected to ground when flat, because the tone board was touching the chassis. The ground is connected to pin 1 via the tone board, loudness board, back to the main PCB and then via a screw above the phono ground. Took me an hour to find where was the physical connection to ground... I had the backl of the unit off at that stage, so I made sure the screw is properly tighten and whadayaknow. Pin 1 connected to ground. Turned it on, voltages on 7062 perfect. Amp IC too, no DC on terminals. Test tone in, headphones out. Speakers in, sound out! And it actually sounds pretty amazing. Loads of bass.
So now I know: check connections to ground properly at the beginning:-)) I think that was the main problem, I believe I broke the transistors and the IC myself. But you have to learn somewhere:-)
I have replaced the broken transistors with new equivalents and the amp still works great. Returned the replacements back to the good amp, now only waiting on the replacement svi 2003 to fit and will have 2 working units.
Thanks very much for your help.
 
Good to see it's fixed.... which transistor and resistor was it?

I did bring up grounding earlier... that series of amp drifts if no ground... V2X and V4X drift if the input plug is unplugged from main board
 
Hi, you did bring that up and that's I went and checked it again yesterday after I run out of parts that could be out of spec.

Gone was q402 and Q502 and one of the resistors R413-414 or R419-420. They are 2 pairs in parallel, one above the other don't know without having the unit in front of me. The one on the picture.

upload_2017-6-16_12-26-11.png
 
Hi, one quick question. What influences DC Offset on these? The amp i repaired and has the donor SVI2003 chip has 5 and 1 mV dc offset. The one that I bought good with SVI2003 A has 35mV on one channel and 8mv on the other. The differences are the chips and q401/402 and q505/502 that were changed on the repaired amp. After a quick listen the amp i repaired I think sounds better. Would the q 401/402 have impact or is it due to the ICs?

Thanks

Petr
 
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