vintage echoplex broken.trying to diy fix. need help

[imo]

i am in the process of refurbishing 2 old echoplexes. Why?? don't really know, like the sound, have a soft spot for old technology.
Anyway, i have one up and working. the second unit doesn't have any echo. I have gone through and tested every component. Replaced anything that looked like it wasn't working. All voltages are pretty close, the unit is wired EXACTLY like the working unit. The heads check out with the right resistance, tried a new tape, etc.
I have been going through with a signal generator and a scope trying to figure out where the signal is dissapearing, i am pretty confident with amps and such, but with this being an echo, its a bit confusing to me. I can provide a schematic if anyone is interested. I have gone through the circuit injecting signal and each part seems to work. Are any of you guys familiar enough with this to help troubleshoot? I have been desoldering, resoldering, scoping, etc, for days now and can't seem to make any headway..
thanks
Ian

[cjlectronics]

Years ago, I worked on an echoplex that was doing the same thing. I pulled my hair out trying to figure out why the signal just died when voltages and signals looked like they should. The problem turned out to be a simple one. The damn ECHO OFF jack is a NC switch and the contacts were just an RCH away from making contact.
Check the ECHO OFF jack and make sure the NC contact is closed or making good contact.

I've got 6 echoplexes that need fixing. They have been on the To Do list for over a year.

CJ

[Enzo]

Good call there.

And also, scope the record bias oscilator - got strong high levels of "RF?" Without the HF bias, things won't record to tape.

[imo]

I love the echoplex. Such a unique sound, even now with all of the digital modelers, like the B3, it is difficult to get the feel. I toured with one for years without a tech, and part of my daily routine was the cleaning, which is funny in retrospect.
I will check the echo off switch. I'm hoping it is there. I think the bias oscillator is working properly. Where is the best place to scope them>?
I have a pretty healthy wave, that seems pretty quick, have to check on the frequency..it is at the bias adjust, at the recording head, at the collecter of Q4.

Dumb question really quick, as i'm not experienced with tape heads. Assuming the head measures the correct resistance, does that mean it is working, or could it measure right and still be dead?

[Enzo]

If the head is not open, it is probably OK.

[imo]

here is the schematic. the hf appears to be about the same as the working unit. the echo off connection is solid. Is there another way to check if i am recording? getting playback? I'm wondering if there is something weird happening in the echo/sos switch, and if i could isolate the signal then i could tell where it is dissapearing.
When i connect the switch at point 1 i lose signal. If i dissconnect I have signal at that point as with the other. Im confused at how this section works. I am assuming that if you were to switch it to the echo side then the SOS black is tied to Echo white at wiper which connects to sos white and ground, and then wire 1 connects to the wiper of the echo sustain. does this sound right?
Ian

http://i85.photobucket.com/albums/k58/ianmoore68/ep3_12961-28591.jpg

[fuzzman93]

Hi Imo,

I like very much Echoplexes too so i've got three of these.One green box(old tube modelEP1)and two EP3 .I've repaired al ot of amps or effects so maybe i could help you .

First plug your gen with 1KHz in the input jack.
Scope at 23,and at 1,the sound goes to the output and a fraction goes to the recording circuit.at this state do you have the correct output signal(the same level than your other working EP3)with the pot full left(No echo),This can be help you to be sure there's no short derivating a part of the signal since it arrive in the recording block.
Well,For the recording block disconnect the record head (don't forget to turn ff the EP3) andthe bias at 3,what happens on your scope ? Signal or no signal?
If yes reconnect the record head without the biais oscillator,what are you seeing on your scope ?
If yes reconnect the oscillatoor circuit then record a10 min of tape(be sure your on off Echo is functional(maybe the sleeve of the jack is earthed on the chassis,this could disable permanently the echo fonction).
Well take your tape off and try it on your other working echoplex,it's the best way to verify if there's a signal on the tape ?no?
If yes the problem is in the playback block .If no ,the record head could be broken or the erase/record head wire or position coulb inverted,don't laugh,if you reverse the wire or the sense of the head(rotate ), the erase head is just after the record head so ,the signal disappear of the tape!
Step by step .First took the the tape of your working EP3 on the broken machine and let it play with a jack in the playback jack control ,no sound at all?check the connection,the switch(for the echo or sound on sound ),put the tip of the probe directly on the echo head ,if there's no signal the head is broken.If yes put the tip on the first transistor of the playback preamplifier circuit and check for cold solder or bad capacitor,check too the voltage on Q1 and Q2,power supply at 7 and finally the pot and the 470pf Cap.

Try this and tell me if you find the problem,i hope this help you!
Best regards
Fuzzman

[imo]

Fuzzman,
thanks so much for the help. I just had a couple of minutes, family day(sunday) but i did check the scope at points 23 and 1. 23 the signal is quite healthy, and shows up so at the output of the unit. point 1 though seems to short the signal out somehow. I have tried changing the echo-sos switch(it seems that the 3 working echoplexes I have checked have a different wiring than the schematic shows) I have checked and checked as to where this signal could be going and i am so far lost.
I will check the record head, bias oscillator. When disconnecting the record head and the blue wire( oscillator) where were you saying to put the scope to see if there was still signal?
Incidentally after messing around with it, and plugging it in to an amp (it looked like i was getting a signal at point 1) i started getting a crazy oscillation with the echo sustain up that sounded like a moog synthesizer with a pitch around 440 hz and moving as i rotated the pot. Entertaining

[imo]

i found the oscillation. In the 20th time of switching the switch around, i reversed the leads so the output pot wiper was feeding into the circuit.
I was actually able to get the echo going a bit, though i still have lots of work to do. I think it was in the heads being misalligned. I now have signal on the echo side, though nothing on the SOS side other than a low rumble.
Definitely learning a lot. I need to read up on tape heads and how they work.
ian

[fuzzman93]

Hi Imo,

The place where you could verify the signal is exactly where the wires are desolder.If the head is dead with ashort,this one could affect the signal even in the circuity.Take out the head wires first then check the oscillator signal.Maybe you'll have to disconnect the oscillator before the biais trap. By this way you should verify the oscillator signal and separatly the signal going in the record head.I've had read before in this thread that without an oscillator signal you couldn't have any record .It's false ,the oscillator signal was a system invented for having a stronger and a cleaner than without it.The oscillator signal is modulated by the audio signal this permit more signal on the tape and finaly avoid distotion.If your record signal is small and dirty this may be a dead oscillator(Transistor,supply or self)For your hum in SOS head ,two things bad earth connection or bad solder on the switching system/head solders . If not ,try to reverse the SOS head with the playback head if the hum stops,it is a dead head.If not you could try to scope at the switch(SOS head connected ) for finding the hum source.I stay at your service!Say to me if your echo comes at live ,i will be happy for you
Best regards
Bruno

[stokes]

Hate to sound overly simple here,but have you tried raising the record level pot?I dont see any mention of it.If I missed it,I appologize.

[imo]

not at all. I appreciate any pointers. I have done that. I actually have completely rebuilt, tested every component, many repeatedly, sat with a scope for hours, adjusted every pot, checked for any possible ground errors, compared both to my working echoplex and my friends, and basically cursed all things good as i tried to understand an echo circuit. It has been pretty maddening, as though i can troubleshoot typical amps, effects, etc, the combination of the tape heads, the oscillator, and the many errors on the schematic have made in a long, laborious process....but.
I actually have echo!!!! I played with the assembly that holds the heads and after bending it down some, i was able to get more signal from the tape. I still don't have a working SOS function but i am pretty happy with this to go on. Definitely know the unit a lot better.


If anyone want to volunteer any info on how the oscillation part of the circuit works, what components play into this, and how, i would humbly bow to your glorious knowledge.. I am jumping back into it either tonight or tomorrow. Will report back soon. Thanks again for all the helpful advice

[stokes]

http://music-electronics-forum.com/showthread.php?t=5666 Heres a link to some basic recording theory.

[fuzzman93]

Hi,

If you erase and the erase head is OK ,the oscillator is working ,try to adjust the biais to have better signal on tape and when is max ,turn just a little the pot in the other way.

[imo]

thanks. I have the bias almost maxed out, and have the echo working pretty well. Thanks so much for your input. I am now trying to go through the SOS portion of the unit and find out where that is dropping out as well.
I think ultimately, after steadying the power supply, and firming up some grounds, etc, the biggest change was made by physically moving the recording head so that it was closer to the tape. thats when i finally started to get the echo again.
Definitely learned a lot.
BTW, Stokes, that link does not work
Thanks
Ian

[Enzo]

The tape should be in contact with the heads, not just near to them. Perhaps the thing is threaded wrong. Tape drags right across the surface of the head.

[imo]

yes, of course, it is in contact with the tape, and threaded correctly. There is a section in the echoplex service manual which talks about how to adjust the record and playback heads manually for the most signal to the heads. this was what i was referring to.
thanks again for the help!
3 mostly working echoplexes now!
IAn

[fuzzman93]

Hi Imo,
And what's about your SOS?I'm so curious !
Thanks

[imo]

I don't have that working yet on the plex in question. Juggling a few things over the weekend. I was also working on the mechanical side, trying to lessen the warble of the tape, cleaning everything, etc. I will give it a go again this week.

[fuzzman93]

Hi,
Don't forget to demagnetize the tape heads and all the tape path,you could win some of clarity and avoid distortion.The tension pad is very important too,on one model i haven't got much sound,the tape path was ok but the tape level was lower than the others machines.I found that the tension pad was loose and i bent it a bit to apply much pressure on the roller.The sound went at the good level to have enough feedback at three o'clock,good very good ,same as direct level,even more!
I put here some pics from my echoplexes,yes i love them !

[stokes]

http://hyperphysics.phy-astr.gsu.edu/hbase/audio/tape2.html heres that link again,I dont know how the other one got there.

[rockinrendell]

what about when the erase head doesnt erase totally? this is the problem im having with my echoplex ep3.

[Enzo]

depends. Does it erase what was recently recorded but not older stuff on the tape already? Or does it just not erase things in general?

If the vertical alignment of the erase head is not exact to the playback head, then the edge of old tracks will leak through. Make a tapeful of something and start the eraser. Now twiddle it up and down to peak the erase level.

Make sure the bias oscillator is strong, and the erase head drive circuit 100%. No weak transistors, no leaky caps, etc. Peak the oscullator voltage - wwhich is a lot higher than you might think.

The erase head is not likely to be magnetized. If it works at all, I tend to think the head itself is OK.

[olddawg]

I have not worked on a lot of echo units (a few) but I have worked on hundreds of Reel to Reel tape decks and cassette players and at one time was a factory authorized Teac/Tascam tech as well as many others major brands. The first thing I would do is inspect the heads and guideposts. Look for any uneven wear or trenching. Also make sure that the pinch roller is not hard or worn or skewing the tape. The next thing to do would be to align the playback tape path. You will probably have to disable the erase oscillator so it will not erase your test tape. Then you need a calibrated test tape which is generally around 10-12 Khz. You can probably cheat by making one yourself from a known good machine recording with an audio generator input at 10-12Khz. Then put a scope (or even an AC meter in a pinch) on the output and align the tape path for maximum amplitude while playing back the test tape. After that install a fresh new tape and align your erase head and erase oscillator. Make sure the erase head has uniform contact with the tape and is not worn out. This proceedure is generally true for all tape decks. You don't have to worry about phase because it is mono. BTW, thoroughly clean and demagnetize everything before you start and when you finish. Make very sure that you are using the right tape formulation.

[rockinrendell]

no it donest erase any of it full strength if at all. when i flip the s.o.s. switch the backgroud gets louder(as it should). it seems to sound ok and echos and plays back just erasing like it should maybe not at all. im not sure about breaking loose the glue to be prying on the head brackets as i wouldnt want to make anything worse. what you said about the tail end of the previous recorded music catching the playback head could maybe have something to it. which head would i realign? how can i check the alignment? im kind of wondering about a weak circut. i took an 8 track tape and cart and pulled out enough to feed through the tape path and put cart where it could feed ok. this worked but due to the way the tape came out of housing it warbled but this was just a test to see if the tape made a difference. it did same thing with no change just was warbled. so im wondering if i can elimenate the tape as the cause? but i do plan on getting another tape to have two carts loaded and i plan on getting some tape to reload myself. i was hoping this was a little more simple so i could solve myself(with everyones help) but its turning out to be possibly more than i can do for it since im not quite the electronic engineers some of you guys are, although i want to learn more.

[olddawg]

no it donest erase any of it full strength if at all. when i flip the s.o.s. switch the backgroud gets louder(as it should). it seems to sound ok and echos and plays back just erasing like it should maybe not at all. im not sure about breaking loose the glue to be prying on the head brackets as i wouldnt want to make anything worse. what you said about the tail end of the previous recorded music catching the playback head could maybe have something to it. which head would i realign? how can i check the alignment? im kind of wondering about a weak circut. i took an 8 track tape and cart and pulled out enough to feed through the tape path and put cart where it could feed ok. this worked but due to the way the tape came out of housing it warbled but this was just a test to see if the tape made a difference. it did same thing with no change just was warbled. so im wondering if i can elimenate the tape as the cause? but i do plan on getting another tape to have two carts loaded and i plan on getting some tape to reload myself. i was hoping this was a little more simple so i could solve myself(with everyones help) but its turning out to be possibly more than i can do for it since im not quite the electronic engineers some of you guys are, although i want to learn more.

As I said before, align the playback tapepath first for maximum amplitude and frequency response with a calibrated tape or whatever you can get with the erase oscillator turned off. Then turn on the oscillator and align the erase head as well as adjusting the erase/record bias. Usually the record bias and erase head oscillator are the same thing.

[rockinrendell]

how do i turn off the erase oscillator? will an o'scope and tone generator do same thing or do you have to use a tape? since im having trouble i was planning on taking to a local repair guy who has the scope and tone generator. just so im clear and as sure as i can be? how do i go about aligning the heads? a lot of info ive tried to gather from the various sites dont seem to address the problem of erasure and the lack of. i know im not the first to have to deal with this.

[olddawg]

how do i turn off the erase oscillator? (there is probably a proceedure in the manual witth a jumper wire but I would just probably lift the B+ to that circuit) Will an o'scope and tone generator do same thing or do you have to use a tape? (You will have to use a factory calibrated tape or make a tape off of a known good machine with a tone generator as an input) Since im having trouble i was planning on taking to a local repair guy who has the scope and tone generator. just so im clear and as sure as i can be? how do i go about aligning the heads? (you adjust the angle and hieght of the head until you have maximum outbut and frequency response) a lot of info ive tried to gather from the various sites dont seem to address the problem of erasure and the lack of. i know im not the first to have to deal with thi.. (magnetic tape will not record without bias. Usually the bias and the erase oscillator are the same) At this point I would suggest that you find a qualified tech. Be careful. When it comes to tape technology many know less than you nowadays.

[rockinrendell]

im suppose to take it in tomorrow. the guy is my age or older. i made sure he has some knowlege and experience with this old technology. which he has, probably hasnt been for while. he does have considerable experience with vcrs which are tape recorders in short too. i will be giving him the info from regis's echoplex page to go by and the links plus i have the service manual downloaded. if him and i cant get it, it may mean a trip to somewhere like orbit or equivilent. any suggestions for reasonibly priced echoplex guys that wont take forever?

[rockinrendell]

what errors are on the schematic? the person who has my unit is going off the schematics.