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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Nov Thu 02, 2017 7:50 am 
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Location: Stephenson County IL. 61032
Sorry guys for disappearing. I needed some time to cool off from this. I ended up putting the receiver away(actually, just moved to my worktable in the basement), and have worked on and fixed a few other "little" things in the mean time. One of them being my meter... I guess the problems it had were just symptoms to a blown fuse :oops: I thought I killed it, and even purchased a (same model) replacement. So, now I have 2 of them digital multimeter's, along with my old analog mm.

The receiver is back on my "normal" workspace and i've already started with some trouble shooting. Too bad I didn't come back to this thread first. I would have tested what radiotechnicion posted. No more working on the unit past midnight :lol: ...and its after 1:30am now so :roll:
"Tape up the test prods, so only the tips are exposed"... That is a GREAT idea. I'm going to do that from now on. I'll probably just leave the tape on them.

I checked what my little stock had, and I found I need to order them little adjustment pots if I replace them. The ones I have are of the same exact type, and they look like they were used...

There are no fuses to my knowledge, except for the main fuse in the back of the receiver.

"how were you measuring the bias?" I was measuring it across those resistors.

Well, here's where I'm at guy's: I pulled the main output transistors and re-ohm'd them and compared to what I had written previously in my notebook. They were all about the same. None of them dead shorted. For S&G's I swapped them from one side to the other and tested the receiver. No change.
Since I remembered someone talking about the driver transistors and possible issues, I decided to ohm them out too.
Well, I found one that leads into the left channel's circuitry that has a dead short. I'm figuring that is/may be the main culprit. Like said above, I still need to check other component's. but, Is it likely that the dead channel is out because of that transistor?

BTW, that transistor is a 2SA546A has an E in a circle after that part number and is also labeled MATSUSHITA, with another E underneath that.


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Nov Thu 02, 2017 7:05 pm 
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Location: Warner Robins, GA
If you replace just one driver transistor unless you find an exact replacement you will need to replace all the driver transistors.


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Nov Mon 13, 2017 9:49 pm 
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Location: Stephenson County IL. 61032
Well, I would like it best if I could find an original to replace with. But, I noticed that the one that blew, in accordance with the schematic is not original. So, id like to find a same model replacement as what blew, or 2 of the original transistors that were installed in factory.

Well, I finally got to testing those requested parts. My results are positive. 8)
R521(100ohm) is at 105ohm,
Q507 I could not find... couldn't even match the transistor. Schematic shows a BF3 in place, but none to be found in actual circuit.
R647(.5ohm) tested at .7 (Same as the rest of them)
Q603(DF2)-allready tested as good. Output transistor
D503(15446)-tested good
Q505(25L4588) tested the exact same as the one on the other channel, so I figure:Good

So far, it seems other parts have all survived. Should I put a wanted add up for my needed transistor, or would that just be a waste of time? I don't know of any other units this transistor could be scarfed from if someone else happens to have some junk receivers sitting around.

I did find a source for "new" Matsushita 2SA546A Transistor's.
http://www.ebay.co.uk/itm/2SA546A-Trans ... 25e0c6a8f3

hmm, fake or fraud :roll:


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Nov Tue 14, 2017 12:30 am 
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Location: Sayreville, NJ 08872
ZackN920 wrote:
Well, I would like it best if I could find an original to replace with. But, I noticed that the one that blew, in accordance with the schematic is not original. So, id like to find a same model replacement as what blew, or 2 of the original transistors that were installed in factory.

Well, I finally got to testing those requested parts. My results are positive. 8)
R521(100ohm) is at 105ohm,
Q507 I could not find... couldn't even match the transistor. Schematic shows a BF3 in place, but none to be found in actual circuit.
R647(.5ohm) tested at .7 (Same as the rest of them)
Q603(DF2)-allready tested as good. Output transistor
D503(15446)-tested good
Q505(25L4588) tested the exact same as the one on the other channel, so I figure:Good

So far, it seems other parts have all survived. Should I put a wanted add up for my needed transistor, or would that just be a waste of time? I don't know of any other units this transistor could be scarfed from if someone else happens to have some junk receivers sitting around.

I did find a source for "new" Matsushita 2SA546A Transistor's.
http://www.ebay.co.uk/itm/2SA546A-Trans ... 25e0c6a8f3

hmm, fake or fraud :roll:

I hope you're using a LR-1500T schematic. There are differences between the LR-1500T and 1500TA schematics and board layouts.
The LR-1500T doesn't use any 2SA546A transistors.
The BF3 and DF3 are the driver transistors. You'll never find them listed on the market with these identifiers. The BF3 (PNP) (Q508, Q516) is 2SA485; the DF3 (NPN) (Q507, Q515) is 2SC485.
Here's the picture again:
Image

In your text above, Q505 is 2SC458B.

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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Nov Tue 14, 2017 3:28 am 
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Joined: Jul Tue 28, 2009 10:52 pm
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Location: Stephenson County IL. 61032
Why do they have to make things difficult!!!

Anyway's, yes I am using a schematic for the 1500T, not the TA version.

This receiver may not originally use 2SA546A transistors, but that's what's in here. It still has the 2SC485 in the other half.

Here's the picture in better clarity so everyone can read and decipher what those top 2 drivers read on them.
Image

:|


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Nov Sat 18, 2017 6:56 am 
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Joined: Jul Tue 28, 2009 10:52 pm
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Location: Stephenson County IL. 61032
So...

No thoughts or anything on what's actually in my receiver?... :roll:


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Nov Sat 18, 2017 6:46 pm 
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Joined: Nov Wed 14, 2007 11:37 pm
Posts: 1320
Looks like "Matsushita"


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Nov Mon 20, 2017 5:58 am 
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Joined: Jul Tue 28, 2009 10:52 pm
Posts: 383
Location: Stephenson County IL. 61032
"oh, hardy-har-har" :lol:




Hey, what could be causing that very light hiss in my right channel after the recap? Since I need to purchase some transistors, if I could find out what's causing it, I can see about finding a replacement for that too.


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Nov Mon 20, 2017 12:56 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 17981
Location: Warner Robins, GA
The hiss would be one or several transistors.

If this has a tape monitor switch turn it on and see if the hiss goes away.

If it does then you know it's before the tape monitor.

If it does not then you know it is after the tape monitor.


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