Oscilator not running in vintage electric organ ? - Page 1
Forum section: electronics / repair

author: gabri.peic
author_rank: Regular Contributor
timestamp: January 16, 2022, 08:13:04 pm
content: Hello. I am working on a "new eko tiger duo" organ and i am having a hard time...So basically there is no output from the master generator at all so i decided to test if the clock pin on the top octave generator was getting the signal. It turns out that there is no oscilation at all. Now i am trying to figure out what could be stopping it from oscillating. I already tried replacing the SN74lS221n monostable multivibrator and some capacitors but still nothing...It started working briefly and i got a proper clock signal but it stopped working before i could even test if the top octave generator was outputing anything. It hasn't worked since.As far as I can see there is really not a lot going on around that ic and i dont know what to do...

author: KevinA
author_rank: Regular Contributor
timestamp: January 16, 2022, 09:28:45 pm
content: I repaired these for many years. The only faults I had were the 5V regulator, the LS221, and the tuning pot.Have you got 5V at pin 16? about 3V at pin 15?

author: gabri.peic
author_rank: Regular Contributor
timestamp: January 16, 2022, 09:40:56 pm
content: There is 5v on the pin 16 of the SN74lS221n but there is only 0.75v on the pin 15.

author: gabri.peic
author_rank: Regular Contributor
timestamp: January 17, 2022, 04:19:08 pm
content: UPDATE: Ok so today i got it running again and it was working fine and giving me sound out of the master generator but when i turned it off and back on again without touching anything it didnt want to start back up (same as the first time when it started working)Funny enough it started working after i pulled out the oscilator ic and i i put it back in while i accidentally left the power on lol .So it seem to me that it has trouble starting up and when it does start it works until the power is removed.So why would that happen?

author: gabri.peic
author_rank: Regular Contributor
timestamp: January 17, 2022, 05:28:33 pm
content: UPDATE 2: I found out what is causing it to start sometimes. When i accidentally shorted colector to base on T101 it started up and woreked until the pwer cycle. It works every time but it can't start on its own for some reson....Hope this gives some clue to someone who is more familiar with this circuit.So the question remains why isnt it able to start oscilation on its own and why does a quick short on the transistor leads wake it up???

author: BrokenYugo
author_rank: Super Contributor
timestamp: January 17, 2022, 09:01:46 pm
content: Posted schematic is too low res to read, it is difficult for anyone to help if they can't follow along.

author: gabri.peic
author_rank: Regular Contributor
timestamp: January 17, 2022, 09:09:00 pm
content: Hang on. I am going to post some better picturec in a bit.

author: gabri.peic
author_rank: Regular Contributor
timestamp: January 17, 2022, 09:28:45 pm
content: Here is a better resolution picture.Note: all the external connections just go to switches, power and ground.If needed or if screenshot of the schematic is still too low i can post the original schematic PDF file, just let me know.

author: BrokenYugo
author_rank: Super Contributor
timestamp: January 18, 2022, 07:12:40 pm
content: That's readable, only thing better would be a complete manual with the parts lists and whatnot. Pics of the board (both sides, multiple angles if needed to see all components) are sometimes nice too.If there are carbon composition resistors (square ended smooth cylindrical body) check them all for drift, they like to drift up, sometimes a lot.

author: gabri.peic
author_rank: Regular Contributor
timestamp: January 18, 2022, 07:34:25 pm
content: I do have a whole service manual and i will upload it later.Here are some pictures of the pcb but pleas ignore some bodged traces (board is horrible and delaminates too easily) , two vertical capacitors in place of the horizontal ones (these really didn't need to be replaced and originals will probably go back in)And the TOG ic had a rough life... Few of its legs got snapped off long before anyone even considered repairing this thing but i was able to solder some leads and put it back into the socket permanently and it works once the oscilator start so i am pretty sure the TOG is good.

author: gabri.peic
author_rank: Regular Contributor
timestamp: January 18, 2022, 09:13:36 pm
content: Here is the whole service manual.I hope this also helps someone else because as far as i can see it is pretty hard to find.https://drive.google.com/file/d/11ZYEP9jpwhThcwjG8flAjhd0RZpRxo6s/view?usp=drivesdk

author: gabri.peic
author_rank: Regular Contributor
timestamp: February 17, 2022, 10:22:34 am
content: Hi everyone. I know it has been a while but i FINALLY got the tone generator running.It turns out i had either counterfit or defective sn74ls221n.Long story short years ago both the tog and sn74ls221n were removed from the sockets for some reson and then when i tried fixing the organ i put them in backwards because sockets were backwards from the factory...Anyway after putting back the original ic the right way it worked perfectly. No more instability.Moral of the story is: always check if the ic is in the right way and don't buy cheap replacements from China.

author: retiredfeline
author_rank: Frequent Contributor
timestamp: February 17, 2022, 11:26:58 am
content: Since pin 8 and 16 are diagonally opposite, you might have blown the replacement 74LS221 chip. Anyway glad you sorted it out.

author: gabri.peic
author_rank: Regular Contributor
timestamp: February 17, 2022, 07:34:23 pm
content: Actually it didn't blow !!! The original ic was put in backwards too. Thts why I thought it was bad. Only thing that happened was that 5v voltage regulator got burning hot. Guess that tiny regulator couldn't prove enough current to blow anything up.

author: Gyro
author_rank: Super Contributor
timestamp: February 17, 2022, 07:38:39 pm
content: Time to mark pin 1s on the PCB with a highlighter before you forget!

author: gabri.peic
author_rank: Regular Contributor
timestamp: February 17, 2022, 07:40:17 pm
content: That would actually be a really good idea.

author: Gyro
author_rank: Super Contributor
timestamp: February 17, 2022, 07:42:39 pm
content: Yes, Sod's law says that it will bite you (or somebody else) at some time in the future.

author: trobbins
author_rank: Frequent Contributor
timestamp: February 18, 2022, 03:25:24 am
content: Moral of the story is: it's ok to buy cheap replacements from China.

author: MathWizard
author_rank: Super Contributor
timestamp: February 19, 2022, 12:34:44 am
content: My grandparents had an nice electric organ. 1 of these days I'll have to take it apart, maybe even check some caps on it.

author: gabri.peic
author_rank: Regular Contributor
timestamp: February 21, 2022, 06:15:26 pm
content: Quote from: MathWizard on February 19, 2022, 12:34:44 amPlease do ! After repairng this one i really see how much work has gone into assembly and engineering on these organs. It is a shame to see them scrapped or parted out. (Unless it is in really bad condition or part donor for better unit).

author: clintrubber
author_rank: Newbie
timestamp: November 01, 2023, 06:01:15 pm
content: Good to read this Eko was repaired again.Related, but not wanting to spend/spoil a new thread on this:anybody ever seen the schematics/documentation of theEKO Minstrel(1968-ish)?(As I thought to have understood the Minstrel may be some kind of 'lite' version of (an earlier version of) the EKO Tiger.The schematics of that one tell already a lot, but in case dedicated Minstrel docsarearound that'd be much appreciated.)Thanks/regards