restoring 1970s panasonic clock radio - Page 1
Forum section: electronics / repair

author: alwayslearning
author_rank: Contributor
timestamp: September 28, 2015, 09:18:51 am
content: my first post here ,i bought a panasonic clock radio from usa and im restoring it which is nearly done but wanted to ask about the 110v and our 240v differences .i understand i could just get a step down convertor but was wondering if i could just replace the transformer inside to a 240v version or am i just wrong about that idea.

author: GNU_Ninja
author_rank: Regular Contributor
timestamp: September 28, 2015, 09:41:08 am
content: Yes you can replace the 110V transformer with an equivalent type with a 240V primary winding. Be aware though that the mains frequency in Australia is 50Hz as opposed to 60Hz in the USA so if the clock uses the mains as a frequency reference it may be a worry. Oh and make sure the replacement 240V transformer has the same or a higher VA (power) rating.Just a thought. It may be the case that the existing transformers primary has existing tapping points to run at 240/220V. ie its primary side could be 110-0-110 with the two sections wired in parallel for 110V operation, in which case, you could just wire the primary side in series for 240/220V operation.

author: alwayslearning
author_rank: Contributor
timestamp: September 28, 2015, 10:00:50 am
content: i had the same radio when i was a kid so it was sold in australia and usa so im hoping theres not alot of differences ,put a pic of the clock .you might be right about the transformer ,i had the same thought as it was sold in both countries so i wouldnt think they would change much if anything at all .will check it out and get back

author: Cliff Matthews
author_rank: Unknown
timestamp: September 28, 2015, 01:22:56 pm
content: To the junk bin I went and pulled this! I suppose the reason it got there was it had 2 SPDT Omron 5-amp micro-switches and a Copal GC-1335 AC synchronous motor that still lives. This one's from 1973 and says it needs 60hz and just 20ma by the markings. You chore will not be small needing a low voltage crystal oscillator to get 100hz, alternate flip-flopping a push-pull pair of transistors to drive an inductor, and stepping it back up to 120v. I'm sure there's other ways, but count the cost.Just found a similar teardown-repair with detailed pic's that may be of help to youhttp://www.instructables.com/id/How-to-Bring-a-1970s-AMFM-Flip-Clock-Back-to-Life/?ALLSTEPS

author: alwayslearning
author_rank: Contributor
timestamp: September 29, 2015, 09:26:37 am
content: looks like it 60hz .might have to just buy a step down converter.need to think about this.

author: BradC
author_rank: Super Contributor
timestamp: September 29, 2015, 09:31:01 am
content: Just re-calibrate your idea of how long a minute is..

author: Cliff Matthews
author_rank: Unknown
timestamp: September 29, 2015, 11:24:17 am
content: Quote from: alwayslearning on September 29, 2015, 09:26:37 amIf the problem was just voltage this would be easy. It's about frequency (50hz) going into a motor who's rotation keeps accurate time by matching it (your motor I see as a shaded pole type). The power stations running the electric grid phase-lock their generators rpm to a master time-base and as long as your motor is not suffering any friction problems, it's accuracy will mimic that of the power grid.

author: albert22
author_rank: Regular Contributor
timestamp: September 29, 2015, 03:42:15 pm
content: Here is a simple 50 to 60Hz converterhttp://www.romanblack.com/one_sec.htmIt is a long page, scroll down to about the middle where you can find the schematic of the converter/inverter with a PIC16F675

author: Cliff Matthews
author_rank: Unknown
timestamp: September 29, 2015, 04:24:31 pm
content: Nice find! The sites a bit oldish but the code's there and many more projects! I see Jameco has the PIC 12F675 for 99 centshttp://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_223781_-1and Instructables has a cheap serial programmerwww.instructables.com/id/DIY-1-PIC-12f675-JDM-Programmer-Cheap-and-Easy/?ALLSTEPS.By the schematic and by the apparent size of the motor, you'll need 2 transformers (30va?) 240v-to-12v CT, some junk bin parts, and a couple of one-dollar low rds MOSFETS to get going. Any speculations on how the motor will respond to the invertor waveform?Question: Is the power consumption listed on the back of the radio? (to know sizing requirements for the mini-invertor - if you so decide..)

author: albert22
author_rank: Regular Contributor
timestamp: September 30, 2015, 06:23:30 pm
content: I am glad that you liked it. That page has a several interesting things. Some time ago I picked up a similar clock for a few bucks but I did not restore yet it because beside the 50/60Hz problem it has broken "leaves". It seems that the plastic got fragile with the years and the little tabs that keep the numbers in place got damaged. I need to figure out a way of repairing them.QuoteOnly the small synch motor needs to be fed with the 60Hz sinewave, that lowers the power requirements for the inverter. Then you can replace the original 110v power supply transformer with one for 240v. May be a little bigger to drive the radio and the inverter at the same time.A little more riskier approach is to put a suitable capacitor in series with the primary to reduce the voltage to 110v. In this case the voltage may vary when the radio is ON but probably that wont be an issue.

author: alwayslearning
author_rank: Contributor
timestamp: October 06, 2015, 11:31:31 am
content: Well its mostly cleaned up and working .now the only problem is the small motor running the clock itself is a bit noisy but was getting quieter the longer it was on and the other thing is the time was 12 seconds out per minute so would that be related to the frequency being 60hz and not our 50 or maybe the noisy motor is the problem or both and thanks to all thats given me advice and help ,i can say ive learned alot from reading these comments .ive been out of this area of knowledge for over 25 years and some of these terms are giving me a good smack around the head but its slowly coming back to me.