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Old 10th December 2011, 10:49 PM   #11
anatech is offline anatech  Canada
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Hi kotofei,
You do have all that gear? Fantastic!! You have no idea how much that pleases me. I will apologize for assuming you didn't, it didn't sound like that from the previous posts. You also have experience working with PCB circuitry, another huge plus.

Okay, so I'll assume you also have troubleshooting experience and a logical approach to what you are doing. This is unusual for someone requesting help the way this unfolded. As for the emitter resistors, you can buy those from some of the repair parts jobbers. Some of the Ebay stores in the far east likely have them as well. Failing that, just buy the non-inductive resistors carried by Digikey (I think) that are the stand up type. Not pretty, but fine electrically. Normal WW 5 watt resistors are inductive, they can cause severe instability depending on the circuit and it's construction.

The transistors that On Semi has are extremely good. Use those. My own supplier I used for 15 years for Japanese parts closed his doors a while ago. We are both in the same boat as far as procuring parts is concerned.

Replacing transistors. Replace everything to the last defective part you find. Then replace one step further back. Also, replace the diff pair with a matched set. They will be damaged due to reverse bias across one. They will test fine usually, but the beta will be changed, and the damaged part may become more noisy. They are inexpensive, but you will need to buy about 10 ~ 20 of them to get good matches. Check the other channel while you're at it. A good match does reduce distortion, the reverse is also true. When testing transistors, check leakage C-E and C-B. Also, reject parts where the beta is way out from normal, high or low - the part is still bad. It also helps to heat parts up while watching leakage C-B, or even beta. This will catch most soft failures that can really ruin your day.

Matching transistors. For outputs, you can use a jig you assemble yourself. Something like the Heathkit IT-18 (or similar) is about the best for testing and matching outputs. You do have to keep the case temperatures the same. For matching signal transistors, another jig is the only sane way to accomplish this. Transistors are very sensitive to temperature, so you must take that out of the equation. I whipped up a simple jig for this, I'd be happy to give you the details. It works so well I've worn out the sockets again, and it's still all ugly built on perf board. Someone should design a PCB for it. Just give me a PM.

The variac can be purchased easily, please do that. You only need about 2 amperes normally, but a 5 ampere model might be the best. Hanging analog meters on it is easy enough. For this, digital meters are not required and too hard to read as things change. Analog meters will allow you to watch tends. Very few people require 10 ampere units or above. If you work on tube amps, or class A types, a 10 to 15 ampere model might be needed. Another thing variacs are great for is to generate the voltage you need from a higher voltage supply. Just a filtered supply for testing amplifier (or whatever) designs that require more than an ampere or so of current. Also good for plating.

Everyone, please do not abuse sample programs. They have already tightened things up in response to this. Much more and they may cancel them altogether, except for the large customers. If you are designing with new products, then use these programs. That is what they are for.

-Chris
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Old 11th December 2011, 10:11 AM   #12
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hei Chris .... good to see you !!!

"""intelligent servo """ ....hmmm i loved that
yeap!! variac is the best way to go I have 3 of them with the bigger to be 3KVA huge id say used for pro amps .....

Chris is right often the things we do happen very fast and are not easy to explain in a non fellow of the cloth ...

best regards from 20 dg sunny Athens
sakis
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Old 27th December 2011, 02:57 AM   #13
kotofei is offline kotofei  United States
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Default Sounds revitalized

Update:

Got output transistors from Mouser, MJL3281AG and MJL1302AG as planned. Another transistors, 2SB631K and 2SD600K to replace bad switching ones, 2SC3467 and 2SA 1370 to replace drivers, and 2SA1516 and 2SC3907 to replace those between drivers and output transistors (“post-drivers”) were purchased from B&D Enterprises.

Then I run into the problem with variac. Specifically with the fact that variacs cost money and I’m broke. So I decided to go with the dumb bulb tester (sorry Chris) and hope for the best. However first I measured voltages at the output connector leading from the power supply to the right channel. All within specs.

Soldered in four new outputs and powered Luxman up using that bulb thing. The bulb glowed for the moment and then dimmed, Luxman display lighted up and then a relay clicked. No smoke or firework display. Powered without bulb- everything seems OK. Measured voltages at output transistors –within specs, same as in the left (good) channel. Supplied 1 kHz signal with the generator and scoped the outputs at low and moderate signal level- perfect sine wave of the same intensity at both channels. Set up bias. Played some music with suicide speaker using tuner as source- plays good, no distortion.

Next, replaced drivers, post-drivers and soldered in new Q544/Q528: they and big switching transistors, Q530 and Q546 were taken out. Powered up with bulb - OK. Scoped all drivers, “post-drivers” and outputs - OK. Measured voltages at Q530/Q546 terminals –within specs.

Then soldered Q530 and Q546 in. Repeated the procedures listed above-all seems OK. Set up bias. Run Luxman for a while then connected 220 W 8 Ohm dummy loads and voltmeter in AC mode to speaker terminals and supplied 1 kHz signal to the CD input.

The maximum power I got from the Lux was 167 Watts from each channel, which correlates well with the expected 160 WPC. Interestingly I didn’t see any clipping by the scope at the max power-rotating of the volume knob further clockwise just didn’t result in the increase of the output voltage. At the max WPC the transformer (?) hummed and the receiver heated up but not as strongly as dummy loads. At 100-120 WPC there was almost no hum and not that much of heat.

Finally re-tested bias checked the DC offset at speaker terminals (OK, less than 10 mV) and hook her up to the main system.

I’m using the Luxman for two days now powered on for long times, playing music at different power levels. Everything seems OK- great sound, no distortion or other adverse effects. The initial smell of burning dust is gone. The time will show; however, I hope I fixed it.
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Old 27th December 2011, 01:40 PM   #14
retrex is offline retrex  United States
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Hi kotofei,
Great news, glad you were able to get it up and running!
Your thread had spurred me to continue on with my own R117 rebuild. I had been picking at it off and on as time permitted for the past two years or so. I did some work on it over the holiday and the below is what I found.
As I stated in prior thread I was able to get the right amp section back up and running and I still had issues with the pre section to investigate. I knew the Tone Defeat switch ( SW401-2) had issues as I was only able to get weak sound out the receiver when I push it in and jiggled it and then held it in. I took it out and tried to deox it, but no go. I then attempted a disassembly to fix it, but the innards were way too fragile, and cheap, so I could not rectify the issue and decided to hard wire the switch circuit into tone defeat mode. I never used the tone controls anyway so no biggie. This got me to a weak but ok sound on left channel and very weak on right channel. I am on the hunt for a parts receiver to replace the switch as I cannot find the particular combination of an in hole, 90 degree plunger activated slider with 4PDT. I think it was a home brew by Luxman through a private jobber.
Further testing on the Tone Control PC Board surfaced that the IC401 (PC4570C-1) Op Amp was not up to snuff on one channel. One channel of the Op Amp had roughly double the resistance of the other, the weak but good channel, so I replaced it with Mouser sourced replacement Op526-NTE891M. I got very good improvement on the weak but good channel and none on the bad right. So on with the hunt for sound.
After much circuit tracing and switching of right for left on various components/boards to ferret out where the sound signal was going, or not going, I traced it to IC382 (TC9163N) on the Function Control PC board. I jumped the feed in from Tape 1 R, which goes into pin 10 of the IC which then gets switched into to pin 12 and I finally got good sound from the right channel. After replacement of the IC with a TC9163AN from Ebayer source I got rewarded with a nice even strong sound from both channels.
In my joy and exuberance I decided to switch from my workbench top testing speakers to a pair of recently repaired Magnepan MGI Improved speakers which serve to provide me with music to work by. I still had the entire front panel of the receiver disassembled and sitting loose in front of the receiver which was facing away from me. Apparently in hooking up the Magpies I shorted something on the front and immediately proceeded to blow the before ok left amp section. One piece of transistor Q521 made a very decent attempt at achieving low earth orbit. In hind sight I should have immediately powered down the receiver and reassembled all the hanging hardware, something that I normally would do. But the thrill of victory and its’ accompanying hubris makes one forget the rules.

Anyway, I replaced the below on the blow left channel amp section with OEM type stock parts and the receiver is back up and running.
Symbol #,Part #,Description
Q537,2SC3281,Shorted
Q535,2SA1302,Shorted
Q533,2SA1302,Shorted
Q521,2SA1370,Blown
R615,330ohm 1/2 watt F.R,Open
R609,.22 ohm 5 watt C.E.,Open
R583,470 ohm 1/4 watt F.R.,Open
R563,1K ohm 1/4 watt F.R.,Open
R561,1K ohm 1/4 watt F.R.,Open
R565,1K ohm 1/4 watt F.R.,Open


Next, after a test period, I think I am going to recap it and upgrade to modern better components just to see just how good this thing can get.
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Old 23rd March 2012, 07:04 PM   #15
retrex is offline retrex  United States
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Default Capacitor Question

I am just finishing up on recapping the Tuner board and there were two capacitors listed as "PP.,0.015pF and "POLY 470pF" that I am unfamiliar with. I googled them and they seem to be, I think, Polypropylene and should only be replace with the like due to tolerance requirements, from what I have read. I checked didgi key and they don't seem to have anything that looks the same. Can I substitute MF equivalent caps?
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