Help! Technics SX-EA5

[Royal]

I have been given a Technics SX-EA5 which looks absolutely brand new inside and out. But, alas...it only hums. It gives out a hum of constant volume regardless of expression pedal position or volume control setting. The main "display" does not work (but its back light does). All other indicator lights work and it seems to respond to all switches and presets as well, but only a hum. The hum does not care which switches/tabs are activated, same hum same volume. No notes from either keyboard or pedals or demos or rhythm settings. I have taken apart and cleaned and deoxidized all inter module connections and switches. All 3 fuses are all good. Unfortunately, I am at a loss,If any of you have any suggestions, they would be most appreciated since I am a tube/valve and wire old guy that can hardly even see all the tiny connections that are made on the components and chips inside. If there is aplace where I may get technical help, that would also be appreciated. I have both the service and operators manuals but they don't help.This organ looks too good to not work (I know, I know, I've said that before and been wrong.) I have listened to a few of these organs on You tube and am fascinated by the variety of sounds (but mine only makes one monotone boring hum), Please help me save this organ from the dump. </P>


Royal</P>

[lparsons21]

Re: Help! Technics SX-EA5



Sorry that organ isn't working right.  Here's a couple of things that come to mind.</p>

1.  Check with headsets.  That should tell whether the final power output is the culprit, or if it is in the overall audio circuit, I think.  Also that will tell whether the problem could be the equalizer board down in the speaker cabinet.  </p>

2.  Just for the hell of it, disconnect the speaker wire running from the upper to the lower cabinet.  That takes the entire lower section out and leaves only the 2 monitor speakers in the circuitry.</p>

#1, and #2 are because it isn't unheard of for a Technics EA5 to have blown speakers and/or equalizer board.</p>

3.  If you have an audio amp or other way of taking the pre-amp output off, then hook up to the pre outs with 1/4" mono plugs to the amp.  Make sure they are mono plugs, stereo plugs won't work as I found out.</p>

The combo of 1,2 and 3 above should eliminate the audio power amp for sure.  But also do some more looking.  I swear I saw 5 fuses listed in the parts diagrams, but damned if I can remember where they were located.</p>

If you have a meter, then read the voltages from the power supply to see that they are all there and proper.</p>

As for tech help, well I guess it depends on whether you can find a sharp local technician and not a parts changer.  If they are sharp, they should be able to wring out the issue, and maybe even fix it.  Not necessarily a Technics guy, but a good solid electronics technician like at a better TV repair shop.  But you have to be careful, because as you know, the cost of a tech could exceed the value of the organ quite easily.</p>

Hope this helps</p>

 </p>

[Royal]

Re: Help! Technics SX-EA5

<DIV><FONT face=Arial size=2>Lloyd,</FONT></DIV>
<DIV><FONT face=Arial size=2>Thanks for the response. At this point I just need someone to hold my hand and talk to about this.</FONT></DIV>
<DIV><FONT face=Arial size=2> First, you are right that the printed circuit board shows 5 fuses. But of F1,2,&amp; 3 on the input power panel ACP, only F1 is hooked up. The others do not even have fuse holders. F4&amp;5 are on the adjacentboard AS.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT></DIV>
<DIV><FONT face=Arial size=2>1. I had done this: no hum through the headset and also no sound.</FONT></DIV>
<DIV><FONT face=Arial size=2>2. Did it, still hum from the monitor speakers. I thoughtthat was curious??</FONT></DIV>
<DIV><FONT face=Arial size=2>3. Will do tomorrow am or maybe tonight sinceUNC is not playing. </FONT></DIV>
<DIV><FONT face=Arial size=2>4. I will also check the voltages tomorrow if I can find some values on the schematic.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT></DIV>
<DIV><FONT face=Arial size=2>What really bothers me and makes me think that it isnot audio is that the display does not work. </FONT><FONT face=Arial size=2>It seems that all the hum is coming from the monitor speakers, with the monitors disconnected and the lowers plugged in, no hum, but no sound. </FONT></DIV>
<DIV><FONT face=Arial size=2></FONT></DIV>
<DIV><FONT face=Arial size=2>I'm not giving up yet. I just hope it is not one of these caterpillar (sp?) looking devices because then I am lost. I once was pretty good at electronics repair (electronics technician USN 1961-1967), - no longer -- most of the components on anything made after about 1975 are foreign literally and figuratively.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT></DIV>
<DIV><FONT face=Arial size=2>Thanks, Roy</FONT></DIV>
<DIV><FONT face=Arial size=2>Got any other ideas, I'm all ears!! </FONT></DIV>

[Guest]

Re: Help! Technics SX-EA5



My first port of call would be the Power supply Card AS5 andcheck that I get a 20vac reading across pins 1 &amp; 2and then Pins 2 &amp; 3. If that is OK Check the raw smoothed DC input to the regulators between of around relative to DC ground +\- 25-30 volts. Then check the output terminals of the regulators Should be +\- 15volts.</P>


There will be anotherregulator somewhere that provides +5v for the digitial IC's. I haven't as yet located it.</P>


I will work on this later and let you know</P>


Without these voltages nothing will work</P>


Hope this Helps </P>


Len</P>
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[fredy2]

Re: Help! Technics SX-EA5



If the hum appears to be 120 Hz, then likely the filter caps have dried out.</P>


If the Hum appears to be 60 Hz, then probably 1/2 of the rectifier has blown.</P>


If the filter caps have dried out, the voltage will dip below what the regulators can handle and the electronics will reset and the displays and everything will be dead.</P>

[Guest]

Re: Help! Technics SX-EA5



Good comment, personally I would attack this problem with at least a scope and an audio signal generator toget a decent visual and generate some tones thru the amplifier.</P>


Chers</P>


len</P>

[Royal]

Re: Help! Technics SX-EA5

<DIV><FONT face=Arial size=2>Rather major progress today. For me at least. As I said earlier there are only 3 "fuses" but there are a whole bunch of fusable resistors. This is a device that I had not seen before (they look like resistors). Found 2 blown resistor/fuses and jury rigged around them for the time being (the service manual says that they were only 6.8 ohm). I previously had no -15vdc. But now I do. Powered it up and voila....I have a display. But, instantly, I blew one of the power amplifier fuses (jut before the speakers). The other amp fuse held. Still had the hum in the monitor speakers. Now all organ functions seem to work (at least on the display). Wondered if maybe both speakers were blown (shorted). Tried a small radio through them. Nothing. Looked inside the speaker cabinet and found that the plug was disconnected (someone has been here before..this was my first sign of it). Both main speakers were bad... open. Very odd I thought. I still had hum through the small monitor speakers with no notes. I obviouslyI now had an audio problem which likely caused 1/2 of the rectifier to previously blow. Unplugged all speakers, plugged in headsets and everything seems to work but at very reduced volume (the headset/line out jacks are powered by a 3rd amp) through the headsets and the same through an external amplifier using the "line out" jacks. I wonder if blown (open) speakers could have damaged the output transistors. So next is to do some serious troubleshooting on the power amp. Quit for a couple of holiday days, went in and played Happy Days are Here Again on my Conn 580. Lloyd, Fred2,and Lenny, thanks for your help. Merry Christmas.</FONT></DIV>
<DIV>Roy</DIV>
<DIV>Does anyone have a PDF of the service manual for a Conn 552?</DIV>

[fredy2]

Re: Help! Technics SX-EA5



The -15 fusable resistor was probably taken out under load of one of the driver transistors for the output transistors which probably shorted.</P>


You need to be extremely careful in re-powering the system.</P>


DO this: Make a bank of flood lights to put in series with the power input. They will act as "fuses" without actually blowing... they just light up if a short develops. This is an old trick... We also often use a Variac to slowly bring up power.</P>


Speakers can short, but the push pull output transistor shorts and "shoot through" is the usual failure. This tries to drive DC through the speaker and will blow protective fuses. Speakers USUALLY don't short unless the voice coil is fried to the pole pieces. Verify cone moves freely without scratching noise by moving GENTLY.</P>


You should replace the fusables with the same part, or temporarily with a small fuse and series resistor. Probably 1/2 amp would do...</P>


When the output transistors fail, the driver transistors often go as well... Miss replacing one and you get to replace them all again if you apply power...</P>
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[lparsons21]

Re: Help! Technics SX-EA5



I think he said the speakers were reading dead open.</p>

I wasn't surprised when he said that, because my 'woofers' in the lower cabinet were open also.  I was lucky in that all I had to do was replace them.</p>

 </p>

[fredy2]

Re: Help! Technics SX-EA5

Verify that the voice coils are open by checking for continuity on the flex leads to the cone... look for evidence of heating of voice coil...

[Royal]

Re: Help! Technics SX-EA5



Fred, Both woofers are definately open. They are Technics about 7 1/2" and marked6 ohm,- I don't think I have ever seen 6's before. They look absolutely brand new, and the voice coils move freely, but are going in the trash. No problem with speaker replacement, I've got plenty. Today, I will be going into the power amp circuitry and see if the power out transistors etc are still good. All clues tell me that the out transistors are shorted but I'll check. I even pulled my old Techtronix mod 310 O-scope out of mothballs after 40+ years. It still works, - I never got into the newer stuff. Can't find my old AF signal generator, since I am only talking AF anyway, any reason I can't just use the Line Out jacks on a small radio tuned to some station that is off the air and transmitting a hum??</P>


Thanks, Roy</P>

[lparsons21]

Re: Help! Technics SX-EA5



Roy, when I replaced my speakers, I just used 8 ohm speakers.  For the most part, going up a bit in impedance on speakers in a solid state system isn't an issue.</p>

And the speakers are 8", well at least the ones I bought to stick in mine are and it was just a simple swap.  I didn't have to do any 're-engineering'... :)</p>

 </p>

[fredy2]

Re: Help! Technics SX-EA5



Remember to use instrument grade speakers. The consumer grade speakers don't take the continuouspower of organ tones very well.</P>


Check the DC balance of the output... chances are you will find it up to one of the power rails due to shorted power transistor..</P>


Old 310... think I have one of those someplace... as well as a 515 and a 545B... The 545B doesn't even have a serial number... Tektronix didn't assemble it... quite a story about that... friend did work for them and they gave him parts for a 545B... he didn't want to take time to asemble it so he gave me the partial assembled 545... I put the parts together and used it for years... have a 465 now...</P>

[lparsons21]

Re: Help! Technics SX-EA5

[quote user="fredy2"]

Remember to use instrument grade speakers.  The consumer grade speakers don't take the continuouspower of organ tones very well.</p>

[/quote]</p>

Hi Fred.</p>

When I replaced my 8" speakers in the EA5, I just used some dual-cone 8 ohm speakers and they seem fine.  When I got them, I compared the build as well as I could by eye, and the voice coil and such seemed at least as good as what the OEM Technics speakers were.  So what does 'instrument grade' entail?  I tried a google search on the term and nothing showed up other than some sellers of instrument speakers.</p>

A curious mind wants to know.</p>

 </p>

[fredy2]

Re: Help! Technics SX-EA5



The speakers that are designed for musical instruments usually have better voice coil design to dissipate heat. It is possible that the Technics doesn't use very good speakers. Some of them have a "ferrofluid" in the gap to help conduct heat away from the voice coil. They cost more of course. Plain old Radio SHack speakers can be torn apart when used on organs. There are companies that make speakers for use in the amps for guitars and PA's that are intended to take the higher sustained power.</P>


A lot of the speakers have edge wound voice coils...</P>