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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Oct Tue 24, 2017 7:17 pm 
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Location: Stephenson County IL. 61032
dberman51 wrote:
All is right with the world.

Your Pyle preamp is intended to drive an AUX input, not a PHONO input. PHONO inputs are for direct connection to a magnetic cartridge. Most 5.1 systems don't have PHONO inputs so you have to use an external preamp, but all hi-fi receivers do.

And no, you can't use the TAPE HEAD input for anything. In the early to mid 1960s, Lafayette sold very inexpensive ($30-70) reel-to-reel reproduce-only tape decks, specifically to play pre-recorded 4-track stereo tapes. They were nothing but a bare transport and play head, no electronics of any kind. So they required a reproduce preamp which the TAPE HEAD input provides. These tape decks were never any good and they're all gone now. Your Lafayette tape recorder has record and reproduce amplifiers, and is intended for connection to the TAPE MONITOR inputs.

So you can button the receiver up, polish it, place it in service, and go on to the next project.

-David

I'm not quite done yet bud :roll:

Yea, I wasn't thinking right away when I was testing with that (Craig) turntable. :oops: I forgot I modified it to work with the 5.1 system, and just plugged it in the Lafayette.
Last night after workout, I plugged my JVC turntable (with no pre-amp) into the Lafayette and it sounded GREAT! :D I also checked that tape hd input and that sounded great too. Not too much difference between sound. Not enough to deter me from using it as another AUX if I could mod it.

Interesting information about those units. Well, I can say that I have never seen one of them tape units (of any kind) that has absolutely no pre-amp of any kind in it. So, they must be near, all-gone as you said.

Woah, hold on there... I'm still waiting for some caps for the unit. I need to change that 5000MFD and the 2000MFD caps along with couple others. I also need to figure out how to do the bias thing...Check it, set it, check the resting voltage, and find what's causing the very slight hiss in the right channel on the main amp at very low volume levels. Not heard if your listening to anything on it.
Also need to figure why my main output transistors are warming up the heatsink on only the one side with no load. With speakers connected and the receiver drivng them at good volume, the whole thing get's warm/hot in operation. I figure that is normal though.


radiotechnician wrote:
If you dare snip one end of both R611 and R612, so you reconnect if you want.

Then jumper out R413 and R436 .

The tape head input will then work almost the same as the Aux input.

THANK YOU VERY MUCH!!! :D That worked and it sounds pretty good! I can now connect another tape deck too that. hmm, I'm still on the lookout for a "Nicely featured" 8 track deck... :wink:


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Oct Tue 24, 2017 8:14 pm 
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You can change those large filter capacitors but many of us have found that they last a really, really long time. Unlike electrolytic capacitors in vacuum tube equipment these are not exposed to either high voltage or high temperature, the enemies of electrolytic capacitors. So change them if you like, but don't expect the unit to sound any different. Now, if it had a hum that might be a different story.

-David


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Oct Wed 25, 2017 2:42 am 
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Back on 10/13 I posted: The DF2/DF45 output transistors can get warm/very warm if the bias and resting current in each channel is not set correctly. The corresponding pots for these adjustments also tend to go bad after many years.

Also, I don't know of any exact replacements for the 2SA485 and 2SC485 driver transistors without probably some circuit modification or part changes. If you notice from viewing the driver transistors, they have a heat sink soldered to the bottom of them. The transistors originally didn't come that way. The output transistors, DF2 are also no longer available and can be replaced with DF45's if you can find any.

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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Oct Wed 25, 2017 7:18 pm 
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dberman51 wrote:
You can change those large filter capacitors but many of us have found that they last a really, really long time. Unlike electrolytic capacitors in vacuum tube equipment these are not exposed to either high voltage or high temperature, the enemies of electrolytic capacitors. So change them if you like, but don't expect the unit to sound any different. Now, if it had a hum that might be a different story.

-David

Really, huh :? Even though they may be approaching 50 years old? hmm. Well, I have no hum... But I am still thinking about changing that 5000. That one IS bulging a bit on the bottom and has stress cracks at the solder lugs. The 2000mfd's physically look good though.
Looking at the schematic, it looks like the 2000's are used in the audio circuits, one for right and the other for left channel. Ive read online that if these caps are replaced with higher value it can improve the sound, especially at higher volume. Any truth to that? or just leave that be, since its good as is?

manualman wrote:
Back on 10/13 I posted: The DF2/DF45 output transistors can get warm/very warm if the bias and resting current in each channel is not set correctly. The corresponding pots for these adjustments also tend to go bad after many years.

Also, I don't know of any exact replacements for the 2SA485 and 2SC485 driver transistors without probably some circuit modification or part changes. If you notice from viewing the driver transistors, they have a heat sink soldered to the bottom of them. The transistors originally didn't come that way. The output transistors, DF2 are also no longer available and can be replaced with DF45's if you can find any.

Yea, I wasn't thinking that when I wrote about the heatsink getting warm again. I know the bias and resting, needs checking and most likely adjusting.
I need to find out where things should be at, and learn how to check them on this unit. So far, I haven't found a service manual for this unit so I'm lost. I got a good schematic, but it doesn't show voltage at any of the test points..

How'd we get talking about the driver transistors again? Looking at mine, I don't see heat sinks that are soldered on.



If I get a new cap to replace that 5000mfd unit, does anyone know where I can get one like the original? With the solder slugs on the bottom? I was looking on Mouser's website and couldn't find any. They have snap in, screw in and another I don't remember, but no solder slugs.


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Oct Wed 25, 2017 8:02 pm 
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Yes, filter capacitors can last 50 years. But they need to be good quality to begin with, and based on your experience with failed electrolytic capacitors in this unit so far, they may not be. So if it's bulging you should get rid of it. And the ones in the audio circuit are speaker coupling capacitors and you should probably change them since failure can take out the output transistors. But I would not increase their value any -- 2000 uF is quite enough.

It's too bad no service manual seems to be available for the bias adjustment, but the schematic does have enough to go on. It shows idle current to be 30mA, a very reasonable number. And with a unipolar power supply like this has, the balance adjustment is done so that the DC voltage at the input of the speaker coupling capacitor is exactly half of V+. To make these adjustments it seems that there are three small (and lousy) potentiometers. They seem to be coarse bias, fine bias, and balance. Start by cleaning them with a bit of Deoxit.

-David


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Oct Wed 25, 2017 11:36 pm 
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ZackN920 wrote:
How'd we get talking about the driver transistors again? Looking at mine, I don't see heat sinks that are soldered on.


Sorry, I didn't mean to sidetrack the thread.
The flanges that the original driver transistors sit on did not come with the transistors. They were considered two separate parts. When replacing driver transistors, you had to unsolder the flange from the bad transistor and solder it on the replacement transistor.


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Oct Thu 26, 2017 7:14 pm 
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All electrolytic caps you have not replaced go ahead and do so.

The adjustment pots on the amp board go ahead and replace them too.

Not necessary to use multi turn pots like I did, but it does make it easier to set the adjustment.

Also after all is said and done and operating as it should the AM and FM tuners will need an alignment.

If you do not have the equipment to do so find someone who does and who can align it properly.


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Oct Fri 27, 2017 4:49 am 
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I'm not going to jeopardize my tuner... I'm not touching that tuner board or multiplex board for now. This receiver has, or damn near has, the best FM tuner in the house. 8) I don't have anyway to perform an alignment, and the only guy in town that could do it is near 90 and ya have to catch him on a good day to do it anymore. That, and as Dberman51 previously said, they don't have nowhere near as much voltage on them and they stay cooler. In a tuner section, I feel this has to be even more so, true. Plus, none in those sections currently look stressed(bulged/leaking/corroded,burn mark), so I think i'll leave them now.
I do want to do the 3 main filter's yet. Still haven't ordered any though, because I can't find any of the same or close value that have solder lugs on the bottom. Maybe I need to install a terminal strip, and just use some that have regular lead's on them. :|

hmm, I gotta look at the schematic and see what the specks are on those pot's. I might have what's needed... Or I may need to order them. First, I need to find out if the original's are indeed bad. If they are all right, i'll just leave them. It's not like they are being turned and adjusted every day.

dberman51 wrote:
Yes, filter capacitors can last 50 years. But they need to be good quality to begin with, and based on your experience with failed electrolytic capacitors in this unit so far, they may not be. So if it's bulging you should get rid of it. And the ones in the audio circuit are speaker coupling capacitors and you should probably change them since failure can take out the output transistors. But I would not increase their value any -- 2000 uF is quite enough.

It's too bad no service manual seems to be available for the bias adjustment, but the schematic does have enough to go on. It shows idle current to be 30mA, a very reasonable number. And with a unipolar power supply like this has, the balance adjustment is done so that the DC voltage at the input of the speaker coupling capacitor is exactly half of V+. To make these adjustments it seems that there are three small (and lousy) potentiometers. They seem to be coarse bias, fine bias, and balance. Start by cleaning them with a bit of Deoxit.

-David

Hmm, stick to 2000. Got it :wink:

I'm glad you found that on the schematic, cause I sure didn't! :oops: :roll:

I'll see about getting to this tomorrow, should have more time.


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Oct Fri 27, 2017 11:41 am 
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Replacing the electrolytic caps shouldn't affect the alignment any and if anything it may make it better.

Just because none are bulging/leaking ETC... does not mean they are not going bad.

Maybe there's a fellow forum member near you who can do the alignment.
.


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Oct Fri 27, 2017 5:28 pm 
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You won't find electrolytic capacitors with terminal lugs. You will have to improvise. You can get solder lugs, screw them down to the capacitors (I assume they have screw terminals, yes?) and connect them that way. Or you can get ring terminals at Home Depot and crimp the connections. You can make it work.

FM tuners, particularly stereo, are really tricky. I suggest that if it's working well, sounding clean, and has good stereo separation, it's better to leave well enough alone. Stereo separation is a good test -- if the separation is good and the audio not distorted that is a good sign that the alignment is pretty close. How is the dial calibration?

There is one electrolytic capacitor in the ratio detector circuit that is important. If it dries out and loses capacity the result will be severely distorted audio on FM, both mono and stereo. If that's not happening, leave it alone.

You don't have to replace the amplifier bias adjustment pots. They are not very good but they should be adequate. Their construction is wide open so they are vulnerable to dust and dirt. So clean them with a shot of control cleaner, rotate them back and forth and leave them about where they were, and proceed to adjustment. More instructions on that when you're ready. You will need two meters.

-David


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Oct Fri 27, 2017 5:54 pm 
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manualman wrote:
The corresponding pots for these adjustments also tend to go bad after many years.


I take that to mean they fail in a way that cannot be fixed and that it is a good idea to just go ahead and replace them.



Also in my opinion when dealing with something that determines whether or not a hard to find part goes bad, adequate isn't good enough.


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Oct Fri 27, 2017 6:32 pm 
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The OP will know if the pots are bad. When he adjusts the bias and balance if the values are jumping all over the place and he can't get a stable reading, then they will have to go. But if they're working......

There is not really a lot to go wrong with them aside from poor contact between wiper and carbon track, Cleaning should fix that.

-David


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Oct Fri 27, 2017 6:46 pm 
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dberman51 wrote:
But if they're working......

-David


Normally I would agree, but when someone who worked on and sold them for a living says a part is known to go bad I tend to heed their advice.


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Oct Sun 29, 2017 7:15 pm 
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Well, all for nothing I suppose :x I think ive killed it...

yesterday/last night I got to cleaning those pots and measuring voltages and what not. I found that the right amp's bias was up. Around 45mA. I adjusted that back down to 30 and it held. Left side was actually low. I think it was around 15 or 18mA. I got that one up to around 30 but it bounced around a bit from 30 to 33 on my meter. Not too bad I thought.
I checked it after awhile and noticed my heat sink didn't really cool down at all, but bias was still... about the same. A little off now after waiting 10 minutes or so. I readjusted it and left it alone again. Seemed good afterword's. Still warm, but whatever. I figured I would post on here about my findings.

Later in the evening, for some reason I felt like doing another round of testing and also measure a few more things. Well, when I went to re-check the bias on the left channel, I got a funky reading of 1 or 2mA. So as I was still holding the one probe at the lug on the output transistor I proceeded to make an adjustment to see if a pot was causing the odd reading. Well, the probe slipped enough to contact another conductive...contact point (or mabey it was the ground, I'm not sure anymore) I saw a little spark. :shock: **deleted** :x
I went to re measure where I was, and got 0.
Image

Well, after playing with the meter(even though it's supposedly fused) I found that it's fried. It reads some whacky ohms when the probes are put together and it makes a constant beeeeeeeeeeep with out the probes touching anything when it is set to diode check.

The receiver.... Dead left channel. :cry: It tries to to work... Only way anything is heard is if the volume is up at least halfway, what comes out is a garbled distorted mess of what it once was.




No,no,no! DELETED :roll: I was very p.o'd with myself and what happened. Just venting I guess. None of that is going to happen. I'm goin' to soldier on. Accidents happen.

oh well though. Thanks for the help :|


Last edited by ZackN920 on Nov Thu 02, 2017 7:23 am, edited 1 time in total.

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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Oct Sun 29, 2017 11:27 pm 
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Post the transistor numbers and I'll see if there are any substitutes.


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Oct Mon 30, 2017 1:22 am 
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Check R 521, Q507, R647, R521. Then Q603 and D503,and Q505.

Then tape up your test prods, so only the tips are exposed.

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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Oct Mon 30, 2017 9:27 am 
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Also do replace those adjustment pots like manualman suggssted.

Provided the amp section has fuses it may jusst be a bad fuse unless the procedure for checking the idle current is like the Lafayette LA series of amps where you remove a fuse and use your meter set to measure current in place of the fuse.


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Oct Mon 30, 2017 5:27 pm 
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How were you measuring the bias? Were you measuring voltage drop across a resistor or did you lift a connection and measure current directly?

I thought I fried a DMM once but it turned out to be an internal fuse.

-David


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Oct Tue 31, 2017 11:58 am 
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If the B+ to each amp channel has a fuse the procedure at least for the Lafayette LA series of amplifiers is to remove a fuse and measure the current.


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 Post subject: Re: Lafayette LR-1500T repair/restoration
PostPosted: Nov Wed 01, 2017 3:03 am 
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Unfortunately the schematic doesn't indicate any fuses in the V+ line. If I were going to adjust the bias on this unit I would have to lift a V+ or ground lead and use a milliammeter, unless I wanted to measure 15 mV across a 0.5 ohm resistor.

-David


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