Typewriter power supply buzzing, not supplying power to typewriter - Page 1
Forum section: electronics / repair

author: 108CAM
author_rank: Contributor
timestamp: March 05, 2021, 05:05:14 am
content: I have an Olympia ES-105 typewriter that I found in hard rubbish and when I plugged it in to see if it worked, the power supply just buzzed and the typewriter wasn't receiving any power.I'm hoping someone is able to help me with this issue because I really want to get the typewriter working.The video in the attachment shows the buzzing noise and specs of the transformer.Note: You'll need to turn your volume right up to hear the buzzing. (Remember to turn it back down after so you don't get startled!)

author: james_s
author_rank: Super Contributor
timestamp: March 05, 2021, 05:20:48 am
content: Is this an iron transformer? Buzzing suggests that it's overloaded, do you have a multimeter to check the output?

author: bob91343
author_rank: Super Contributor
timestamp: March 05, 2021, 05:21:06 am
content: You have to either get a service manual or reverse engineer it. Otherwise, there is no clue how to repair it.

author: salbayeng
author_rank: Frequent Contributor
timestamp: March 05, 2021, 05:38:08 am
content: Buzzing probably due to a short circuit somewhere.Cut one of the low voltage transformer wires and put in a light bulb of appropriate voltage, e.g. if 24v then use a 24v 20W bulb (or 2 x 12v bulbs) , wattage of bulb depends on transformer size, if it isa 2" cube then use a 20W bulb, if 4" cube , use 100w bulbs.If there are three wires , then insert bulb on the "centre wire" it might be black where the other two are yellow. Otherwise use ohmmeter to find center.When you power up , the bulb will light up and buzzing should stop. (If you are using a centre connection, and it still buzzes and bulb doesn't light, then your bridge rectifier is shorted). At this point you will probably have about half a volt across the main supply capacitor, then you just follow the PCB traces to figure where all the current is going. for example you might have 500mV at the filter capacitor , then 490mV 2 inches away then 480mV on a left branch and 490mV on a right branch, so keep following the branch with lowest voltage. The same method can be used on the ground rail, except the voltage will steadily increase as you get to the fault, then stay static, e.g. 10mv-20mv-30mv-40mv-40mv-40mv-40mv so start looking at the first node with 40mV. This approach is commonly known as the "millivolt method".You can also just connect a lab supply set at 5v, 1A to the filter capacitor, and use the same method, this removes the hazard of 240v wiring.Actually before you do all this try measuring the bridge rectifier with the diode range on your DMM. (Power off , of course ) a good bridge will show ~0.6v if red terminal on either AC terminal and black on + , and also if black terminal on either AC terminal and red on -, it may take a few seconds for reading to stabilise.

author: 108CAM
author_rank: Contributor
timestamp: March 05, 2021, 05:39:40 am
content: I do have a multimeteris the output AC or DC voltage?the output cable is a 5 pin connector and I dont know whats whatI'll see if I can get the circuit board out of the metal thing so I can get a better look at it

author: salbayeng
author_rank: Frequent Contributor
timestamp: March 05, 2021, 05:42:20 am
content: It's pretty old, 1984 by the date codes.Possibly some of the mechanism is jammed because the grease has dried up.A motor somewhere might be trying to go home and open a limit switch.Wriggle the motor shaft , and linkages you can find, and see if there is anythinmg jammed up.

author: 108CAM
author_rank: Contributor
timestamp: March 05, 2021, 05:46:38 am
content: the power supply buzzes even after I disconnected it from the typewriter

author: salbayeng
author_rank: Frequent Contributor
timestamp: March 05, 2021, 05:48:04 am
content: Quote from: 108CAM on March 05, 2021, 05:39:40 amDo you have a good photo of the connector and wires going to it, the function can usually be guessed by the wire colors and sizes and what they are next to.You might have two thick brown wires for the main motor this might be a 24v or 12v motor.and two thin yellow wires for the logic to make 5v for the computer chip inside.and a green wire for ground (ora black wire for common) .

author: 108CAM
author_rank: Contributor
timestamp: March 05, 2021, 05:52:32 am
content: pin diagrampin 1- blackpin 2- greypin 3- redpin 4- brownpin 5- blue

author: salbayeng
author_rank: Frequent Contributor
timestamp: March 05, 2021, 05:52:54 am
content: Quote from: 108CAM on March 05, 2021, 05:46:38 amSometimes a normal transformer buzzes because it vibrates against the chassis, (possibly the transformer got bent a bit when tossed out)If you push hard on the transformer witha wooden stick, does the buzzing stop?Does the transformer get stinking hot after a few seconds - then the transformer might have a shorted turn. Usually you can see bulging/discolored plastic somewhere on the transformer if so.

author: salbayeng
author_rank: Frequent Contributor
timestamp: March 05, 2021, 05:59:49 am
content: OK the wire colors look pretty random,With the power off , measure the resistance between different wire colors , with 5wires you should get two windings, one of which is a centre tap. Also check if any wire connects to the metal of the transformer.Use the low ohms range e.g. 20ohms, and short your meter leads together to check your zero reading, it its more than 0.5ohms you need better leads , or maybe just jiggle them.Also a good picture of the area around where the plug goes on the PCB might help.

author: 108CAM
author_rank: Contributor
timestamp: March 05, 2021, 06:04:42 am
content: there was no heat, burning electronics smell or smoke.hitting the transformer had no difference although the angle i had the transformer made the buzzing louder or quiter depending on the angleEdit: i just realised i was meant to push the transformer, not hit it. the pushing did reduce the noise a bit

author: salbayeng
author_rank: Frequent Contributor
timestamp: March 05, 2021, 06:20:32 am
content: If your "transformer" looks like this, then it is actually the whole power supply, and the plug you have will be DC voltages to the rest of the typewriter.from here , different typewriter , just looking for a general schematic,http://www.bitsavers.org/pdf/olympia/typewriter/electronic_compact/Olympia_Compact_Electronic_Troubleshooting.pdf

author: salbayeng
author_rank: Frequent Contributor
timestamp: March 05, 2021, 06:29:13 am
content: Quote from: 108CAM on March 05, 2021, 06:04:42 amProbably normal behaviour then, if it is not hot. Transformers in metal boxes can develop annoying buzzes, can usually moderated by wedging a toothpick in the appropriate place, the buzzing might be a red herring.I've done a bit of googling to try and find a generic electric typewriter schematic, and found nothing.Does your typewriter have hammers like a normal typewriter, or a cylinder with the characters on , or a daisy wheel?At the moment looks you need to find a friend who has a bit of electronic service experience, these older units were pretty simplistic and robust, might just be a blown fuse somewhere.

author: 108CAM
author_rank: Contributor
timestamp: March 05, 2021, 07:11:38 am
content: i reinstalled the power supply and the typewriter still wont workwhen i unplug it, i do hear a high pitch hiss

author: amyk
author_rank: Super Contributor
timestamp: March 05, 2021, 02:20:31 pm
content: Check where the voltages go. I don't know how much electronics these have but you'll need to do some more reverse-engineering to figure out what needs to receive power.

author: james_s
author_rank: Super Contributor
timestamp: March 05, 2021, 11:28:47 pm
content: Do you know anyone who has some basic electronics knowledge and experience fixing things? This is one of those situations where it should be trivial for a person that knows what they're doing to get at least a basic idea of what's wrong, but trying to troubleshoot remotely via forum posts is almost impossible.