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Old 11th December 2011, 07:48 PM   #11
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Default still hoping for a miracle.

Tested it with the aux and dat input with an external CD player. it seems as is the volume is a bit higher, is still very low, have to max it out to hear it. fidelity is great though.

I wonder if it's the actual potency/amp?
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Old 12th December 2011, 07:02 AM   #12
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You have to do a real measurement on this. I can't see any normal fault giving low gain on both channels. Without hearing it, it is impossible to gauge what you mean by "low volume" so measurement is the only way to get a definite answer.

Any DVM is tolerably accurate at the voltages we are talking about and will give a ball park figure. You must use a test frequency of around 50 to 400hz as that is guaranteed within frequency range of any DVM. And it must be sinusoidal for accuracy.

Watts = V squared/R so first measure the AC voltage across the speaker terminals with NO speakers attached using a known test CD with tones on it. By rearranging the formula to give,

V = Sqr root (Ω * W)

we can say an amp of 20 watts RMS should produce just over 12 volts RMS.

Turn the volume up slowly untill it begines to "limit" and show no further rise as the control is turned.

If that is OK the next step is to then to reduce the level to around 3 volts and make sure that adding a speaker does not pull that voltage down. 2.83 volts RMS is one watt into 8 ohms and is "loud".
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Old 12th December 2011, 08:43 PM   #13
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Moonly, thank you for your reply. I will do those tests but first I wanted to tell you that yesteday I was able to make it work for a few hours.

I plugged an external CD player to the aux to test if it worked and it had the same issue as the regular cd. Had to turn the volume all the way up to hear it (almost like a record without being amplified). but a few minutes after that, with the volume maxed out, I heard like an explosion in the speakers. Somehow it triggered it. The radio came to life and so did the CD. I had to turn the volume all the way down. It worked perfectly for hours. I turned it on and off with intervals of 5 to 10 minutes and it seemed ok as long as it was still warm. After leaving it off for about an hour, turned back on and it went back to the very low volume.

so what I get from this is that the radio and CD are both affected by the same volume issue, (the radio doesn't tune when this happens, it's absolute quietness and no signal at all), so there's got to be a component or part that is not doing it's job triggering the amplifier to work or something not making the right contact unless you mess with a few things here and there. I've had similar issues happened before in other receivers where you had to turn the volume all the way up in order to "trigger" or "unclog" the normal volume but I never new what it was. What do you think, do I still have a chance to save this great little receiver? thank you!!
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Old 13th December 2011, 07:03 AM   #14
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The fact that it has now worked show that it is capable of doing so.

Two things come to mind,

1. That there is a physical issue such as cracked print somewhere, although tbh it would be unusual for both channels to be affected.

2. Is there an electronic "mute" or attenuator. If the unit has remote control then that is likely. If so there may be an issue here. It could be going into mute.

3. And another thought... does it have an output muting relay in series with the speakers ? The contacts could be tarnished. If it does it again then tap the relay hard with a screwdriver handle and see if it "corrects" it. You may be able to dismantle the relay to clean it. That is quite a common problem on a lot of equipment.
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Old 30th January 2012, 04:08 PM   #15
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Default Old Sony MHC 1600

Mooly, thank you so much for you replay. It's been a few weeks and I still haven't given up on my old sony. I'm determined to repair it.

I opened the receiver and did not find anything cracked or unusual, in fact it It seemed pretty clean for being that old.

The remote does not have a muting button or feature, and I couldn't Identify the relay to tap it.
After doing some troubleshooting, I found a few interesting things:

The volume knob doesn't move when I use the remote, which leads me to believe that there is something in that particular area that is not transmitting electricity the way it should but at the same time, the volume knob doesn't move even when there is sound coming out and everything seems to be working.

Another detailed tip: when I play a CD, I can see the actual EQ level bars on the lcd screen moving and extremely low sound that can only be heard by turning the volume knob all the way up to the max.

With the radio is different, when "it works" I see the EQ Bars on the LCD display and everything sounds fantastic. When the volume shuts down the bars don't show up anymore, almost like it's not getting a signal at all, but the CD still show the bars with the low sound described above. same as CD with an AUX input.

Help help help??? I really appreciate all your feedback, thank you!!!
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Old 31st January 2012, 07:54 AM   #16
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Never give up

My immediate thought on this with you saying the radio is OK and so on.... is that one possiblilty could be cracked or damaged print. Rereading your earlier post it did work intermitently too on CD. Maybe worth carefully pressing/bending the PCB's with it playing.

The volume control... look at it closely... does it use a motorised pot or is it a "rotary encoder" If you can spin the knob round and round with no end stops then its an encoder and the knob itself would not physically move as the control is purely electronic. If motorised it should move and so if you are sure the remote is 100% good and transmitting OK then maybe look at why the motor doesn't turn.

I think you are going to need the circuit details and tbh a scope would be the minimum test gear needed to help locate this problem.
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Old 31st January 2012, 08:57 AM   #17
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This unit will definitely need resoldering. The board on which the display sits has smd ics that will need resoldering.

The graphic EQ ic which is fitted on the right side vertical pcb runs hot and will also need resoldering. Be careful not to damage the flat cables.

Do one check. Find out whether u get output at DAT OUT feeding signal at video/aux as source. U can also open up the unit and find whether the REC OUT level is good enough. U can look for it on the connector of the right side vertical pcb.

The set uses STK4132II

I have this stereo and presently is used as a premp for my low TIM amp. I just tapped the STK input signal and connected it to the DAT OUT RCAs by cutting the original tracks. This can be easily done by opening the top and back cover.

I bought this second hand nearly 10 years back and first thing I did was resoldered it.
My tape deck display does not work but functionally ok but for the pinch rollers(unobtainium)

Uses a motorised potentiometer and not a rotary encoder. Mine was also not turning low and the culprit is the 0.22 Farad storage cap on the front pcb. It corrodes the surroundig tracks. I suspect most of your problems will be near this cap.

There is no relay in this unit.

Gajanan Phadte

Last edited by gmphadte; 31st January 2012 at 09:05 AM.
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Old 31st January 2012, 10:25 AM   #18
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Quote:
Originally Posted by schmegegy View Post
Hello: I too, have an MHC-1600. The cassette deck does not work. When I turn it on and press the play buttons, the decks just turn one way and then stop and turn the other way--back and forth, back and forth. This happens on both A and B. As others have mentioned, Sony has no information, no parts, no help. There is a "manual" if you believe that telling you what each part does, is a manual. I'm looking for a parts manual for the inside of the deck, not just the buttons and lights. I have a genius friend who will fix it if we can find the parts. But I can't even find a schematic of the inside, let alone, parts.

Can someone help! I do have cassettes that are no longer in print as records--such as Radio Breakfast. I would love to play it.

Thank you.
Schmegegy
Did u check the belts and the pinch roller...
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Old 31st January 2012, 03:00 PM   #19
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Default I fixed it!!!

Finally I came down with a solution thanks to all your help and I wanted to tell you about it.

After checking everything Mooly and gmphadte suggested, I went back to the earlier posts that mentioned that the issue may be that the receiver may be going into "mute mode"
there's no "mute" button on the remote, but I found the mute on the actual print inside. Basically I tested it with a wire from mute with some other contacts (touching them at the same time, until it actually bypassed it. I soldered it and it works, CD, Radio and DAT in. I will post a pic of the not so elegant solution later in the day. what do you guys think? will it last?

Again, thank you for all of those who posted possible scenarios and helped me troubleshooting the issue.
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Old 31st January 2012, 06:28 PM   #20
Mooly is offline Mooly  United Kingdom
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It's good you have found a solution of sorts. It should last if you are bypassing some muting circuit or forcing a logic level.

As long as you happy, that is all that matters
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