Luxman T-110U Tuner Right Channel Out

[gabrielsand]

Hello To All!
Hope someone can help me with a dead channel issue. I purchased said tuner from Ebay knowing there wasn't audio from any of the channels. I'm no electronic tech but like to tinker on things.

Testing the various components starting with the diodes, I found one diode defective. Replaced it and had sound coming steadily from my left channel but intermittently from the right. Further testing revealed some resistors were out of spec so I replaced those with the proper wattage ones. Same result, steady sound from the left channel, right channel cutting in and out. I decided to change all the electrolytic caps, again no positive results. Matter of fact the blinking dial pointer doesn't blink anymore and when I press the muting switch in the dial pointer light increases in brightness. Measuring the voltage with the switch depressed is about 12v, released is 6v. I triple checked my work ensuring I placed the right values of caps observing correct polarity and resistors where they should be, all seemed fine. Oh yes, the right channel is no longer intermittent, it's totally dead now!

Checked wires for continuity, connections solid, cleaned pots (not the ones in the sink) and re-soldered circuit board connections. I'm thinking now it's a transistor or IC chip that's faulty. Without removing transistors from the board, I measured them using a multimeter set on the diode setting. All seemed well. Perhaps They need to be removed from the board and retested, would that give more accurate results? I'm running out of options perhaps someone can enlighten me on steps to take. Thank you in advance!

 

[DF96]

In order to fix a fault you first need to find the fault. Changing everything simply introduces new faults, as you have found.

 

[gabrielsand]

Sigh! At least I've sound if only on one channel. I attempted reading the schematic but what I downloaded was difficult to read due to lack of sharpness in the print. I've the Luxman service manual but it doesn't go into detail on how to test, just gives numbers. I wish I had a simple, clear path to follow instead of guessing and throwing parts at it. Any ideas?

 

[anatech]

Hi gabrielsand,
Remove the transistors and test for beta. In circuit testing can often hide problems and the only thing you will know for certain is if there is a dead short or not.

DF96 is quite correct, you only create extra issues if you do work before troubleshooting the problem. What you did is something we call "shotgunning". Those kind of techs only luck into repairs and never learn anything as they work.

There are sometimes polystyrene capacitors that are in the output filter from the MPX chip. They have very fine leads and are often clear with silver foil or plating inside. These can short. They are also extremely temperature sensitive. It's easy to short them by heating up their leads more than a good tech can solder them. The types that were used in tuners seem to have very thin dielectric that fails more often. When replacing these, use the same type at 50 VDC or higher rating. Never use them in places where there is a lot of heat. They can be replaced with Polypropylene or similar types. These have a very large effect on sound quality as they are close to being the "perfect capacitor" for audio signals. They are not the best for many other things.

Simple paths exist once you gain the knowledge. When you are learning, things are always more difficult. Now, do you have an oscilloscope? You need one for this.

-Chris

 

[gabrielsand]

Thank you for your response and help Chris!

Yes, I'd rather learn than "shotgun". Only John Wayne could do that! I do have a Velleman HPS 10 Handheld Scope, perhaps that would suffice? I guess I'd better bone up and get a crash coarse on oscilloscope usage. Would a in/out of circuit transistor be enough? There are many analog ones on Ebay including inductance types, can you recommend a good brand?

 

[anatech]

Hi gabrielsand,
I'm not sure where you have got to with this, so let's answer some questions.

The handheld 'scope might do it. If not, grab a new Rigol or Keysight (Agilent - HP) oscilloscope. Do not bother with the USB wonders. They are easy to kill.

Used 'scopes. Tektronix, HP or Agilent, Philips (PM30xx series). The next are okay. Kenwood, Leader, B&K. There are others that are less desirable but might serve to get your feet wet. It does not pay to buy an unknown or cheap brand of equipment.

Transistor testers are out of circuit only for a real meaningful test. In circuit testing can show you dead shorts or possible open circuits. Old Heathkit testers are pretty good. Some of the Chinese testers on Eeeekbay that use a ZIF socket (Zero Insertion Force) are better. Try to get one of these that only test transistors if you go this route.

A good multi-meter! It really pays to get a good one. With these, Fluke, Agilent / Keysight are about the best. The others really are substantially less good meters. Unless the meter is an expensive one, consider capacitance ranges with great suspicion! Older Fluke 87 series, or HP meters are extremely good. I have some of both, and a new Keysight (fantastic meter!). The older HP 974A is wonderful. You can get these used and they are generally in great condition. The basic DC accuracy is 0.05%, and they are good on AC ranges to 100 KHz. That spec. is hard to beat. The Fluke 87 and 85 I have are good meters, but I enjoy using the 974A's far more.

-Chris

 

[gabrielsand]

Hello Chris,

Thank you for taking the time in posting this valuable info, I will definitely look into your recommendations.

At the present, I've a Velleman DVM850BL multimeter, a Sencore Cricket (not the Super Cricket!) bought through EeekBay (so aptly named -you pay your money,you takes your chances) that arrived dead as a parts or repair unit, and a Sencore TF-166 that awaits testing to see if its operative, which was claimed to be and appears to have been hardly used. All bought at so-called 'bargain' prices. You plug these things in, hide, hope it works and doesn't explode! Well, got to start somewhere on a limited budget with the hope the repairs are simple on these units.

As an ongoing tinkerer in electronics, it appears I'll just have to bite the bullet and obtain quality, reliable equipment as you suggested to avoid frustration and the hassles.

Regards,
Gabriel