UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Radio (domestic)

Notices

Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

Closed Thread
 
Thread Tools
Old 30th Jun 2022, 11:38 am   #41
G6ONEDave
Octode
 
G6ONEDave's Avatar
 
Join Date: Dec 2019
Location: Owston Ferry, North Lincolnshire, UK.
Posts: 1,689
Default Re: Samsung 3 band radio cassette, model: STF55L

Hi Malcolm,
I'm slightly confused with a voltage reading from your post 32. In it you say that IC201 pin 11 has 0.63v on it. It should be around 5v, if the voltage is correct at 0.63 then the problem is the silver paint track acting silly. The cure for that is to solder a thin insulated wire between pin 11 of IC201 and the point where the pcb through hole at PR206 is. This end of PR206 that is furthest from the switch.

Please check the volts on IC201 pin 11 again to confirm the situation. You are measuring volts so you want the black meter lead on the switch body. Pin 11 is the middle pin of the IC201 on the right hand side, with the ident at the top of the chip. If you are measuring from the print side and you have the ident at the top then it's the middle pin on the left.

Dave
__________________
Quote "All is hyperthetical, until it isn't!" (President Laura Roslin, Battlestar Galactica)
G6ONEDave is offline  
Old 30th Jun 2022, 2:25 pm   #42
Formby Mal
Tetrode
 
Join Date: Mar 2022
Location: Southport, Merseyside, UK.
Posts: 59
Default Re: Samsung 3 band radio cassette, model: STF55L

Hi Dave, Thanks once again. Maybe I got the wrong point on the IC201 so I have done it again and have attached a diagram, with results, and a photo of where I did the test on the component. It was on the right side and starting from the bottom - where it says 9. Cheers Dave, Malcolm.
Attached Thumbnails
Click image for larger version

Name:	IC201 volt test.jpg
Views:	48
Size:	91.8 KB
ID:	260152   Click image for larger version

Name:	IC201 results.jpg
Views:	36
Size:	14.8 KB
ID:	260154  
Formby Mal is offline  
Old 30th Jun 2022, 3:30 pm   #43
G6ONEDave
Octode
 
G6ONEDave's Avatar
 
Join Date: Dec 2019
Location: Owston Ferry, North Lincolnshire, UK.
Posts: 1,689
Default Re: Samsung 3 band radio cassette, model: STF55L

OK you now need to see what the voltages are on both ends of PR209 and PR7 which are both 100 ohm resistors. These are again those black carbon paint jobs with the silver paint at each end. PR7 is near to pin 1 of IC201 on the component side. PR209 is again on the component side next to a pre set resistor and between it and 2 electrolytic capacitors. These caps are located at the pcb edge near to the lever of the bandchange switch S1-5. Go to the switch lever and then to it's side there is a wire link J05, then the 2 caps and then PR209 and then the pre-set resistor R252.

These voltage checks are all a case of elimination and should show where the problem actually is.

Dave
__________________
Quote "All is hyperthetical, until it isn't!" (President Laura Roslin, Battlestar Galactica)
G6ONEDave is offline  
Old 30th Jun 2022, 4:49 pm   #44
Formby Mal
Tetrode
 
Join Date: Mar 2022
Location: Southport, Merseyside, UK.
Posts: 59
Default Re: Samsung 3 band radio cassette, model: STF55L

OK Dave finally found PR209 it was underneath 103, it's volts started to climb and stopped at 92.4 and the PR7 volts are 95.8.

Cheers Dave... Malcolm
Formby Mal is offline  
Old 30th Jun 2022, 5:12 pm   #45
G6ONEDave
Octode
 
G6ONEDave's Avatar
 
Join Date: Dec 2019
Location: Owston Ferry, North Lincolnshire, UK.
Posts: 1,689
Default Re: Samsung 3 band radio cassette, model: STF55L

Malcolm, those voltages cannot possibly be correct. They can't be more than 9.4v as thats the power supply output. So given that there is a resistor between the 9.8v supply and the those resistors you should be expecting around 6v at the input end and perhaps 3 or 4v at the other end. Make sure that you have the meter black lead on the switch body and use the red lead to take measurements with. You want the 20v DC meter range.

Just out of interest if you have the black meter lead on the switch metal body and the red lead not connected to anything what does the meter show on it's display. It should be zero or possibly 0.1 to 0.9 maybe. If you're getting 92.4v or 95.8v then there's something very strange and wrong.

Dave
__________________
Quote "All is hyperthetical, until it isn't!" (President Laura Roslin, Battlestar Galactica)
G6ONEDave is offline  
Old 30th Jun 2022, 5:39 pm   #46
Formby Mal
Tetrode
 
Join Date: Mar 2022
Location: Southport, Merseyside, UK.
Posts: 59
Default Re: Samsung 3 band radio cassette, model: STF55L

OOPS yes your right sorry Dave... that was the ohms readings. The VOLTS readings are... the PR7 at the bottom, near the IC201, it is 5.18 and at the top it is 5.18 and the PR209 the right, nearest to the switch S1-5, it is 5.86 and the left it is 5.20.
Once again sorry... Malcolm.
Formby Mal is offline  
Old 1st Jul 2022, 10:17 am   #47
G6ONEDave
Octode
 
G6ONEDave's Avatar
 
Join Date: Dec 2019
Location: Owston Ferry, North Lincolnshire, UK.
Posts: 1,689
Default Re: Samsung 3 band radio cassette, model: STF55L

Hi Malcolm,
Well PR7 looks slightly odd on the voltage readings as there is nothing being dropped across it volts wise.

Next checks on volts not ohms are on PR6 and PR1, they are both between the end edge of the pcb and IC1. This is the integrated circuit that in post 32 you said had zero volts on it. PR1 and PR6 both supply volts to this chip via PR7. We now know that we have supply coming out of PR7, hence the next step.

Remember you want the black meter lead on the switch metal body again for these measurements.

Dave
__________________
Quote "All is hyperthetical, until it isn't!" (President Laura Roslin, Battlestar Galactica)
G6ONEDave is offline  
Old 1st Jul 2022, 11:20 am   #48
Formby Mal
Tetrode
 
Join Date: Mar 2022
Location: Southport, Merseyside, UK.
Posts: 59
Default Re: Samsung 3 band radio cassette, model: STF55L

Hi Dave, OK I’ve checked PR6 & PR1… PR6 left point is 5.15 volts and right point is 5.15 volts. PR1 top point is 0.0 volts and bottom point is 5.15 volts.

I also checked the IC1 volts again to be sure…
1 to 4 points & point 7 are showing 0 volts... but points 5 & 6 are showing 5.14 volts. So I couldn't have got a propper conection when I did the test earlier (re post 32) sorry.

Cheers Dave…. Malcolm.
Formby Mal is offline  
Old 1st Jul 2022, 11:34 am   #49
Formby Mal
Tetrode
 
Join Date: Mar 2022
Location: Southport, Merseyside, UK.
Posts: 59
Default Re: Samsung 3 band radio cassette, model: STF55L

Dave, I also did another check on the IC201 volts and have attached a diagram.

Cheers, Malcolm
Attached Thumbnails
Click image for larger version

Name:	IC201 volts.jpg
Views:	28
Size:	36.4 KB
ID:	260200  
Formby Mal is offline  
Old 1st Jul 2022, 11:52 am   #50
G6ONEDave
Octode
 
G6ONEDave's Avatar
 
Join Date: Dec 2019
Location: Owston Ferry, North Lincolnshire, UK.
Posts: 1,689
Default Re: Samsung 3 band radio cassette, model: STF55L

Hi Malcolm, Those voltages around IC201 are much more like the ones in the manual voltage table and look reasonable.

The voltage on PR1 looks wrong, you should have around 5v at one end and 3.4v at the other end. Next do a resistance check on PR1, it should measure 330 ohms or a little less. This is with the red and black meter leads across resistor PR1. Also whilst you are in that location using the ohms range of your meter connect the black lead to the switch metal body and take the red lead to the end of PR1 that is giving 0v. This second test is to check that C2 has not gone short circuit or even IC1 pin 2 has not gone short to earth.

Dave
__________________
Quote "All is hyperthetical, until it isn't!" (President Laura Roslin, Battlestar Galactica)
G6ONEDave is offline  
Old 1st Jul 2022, 2:50 pm   #51
Formby Mal
Tetrode
 
Join Date: Mar 2022
Location: Southport, Merseyside, UK.
Posts: 59
Default Re: Samsung 3 band radio cassette, model: STF55L

Hi Dave…. The first ohms test you asked for with the PR1, with red at one end and black at the other, shows 0 ohms, .…. well it starts out high 192 – 150 then drops to 0. The second test with the black lead on the switch metal body and the red at the top point where it showed 0v is showing 0 ohms… again that started off high then dropped to 0 ohms.

Once again Dave thanks very much for all this….Cheers…. Malcolm.
Formby Mal is offline  
Old 1st Jul 2022, 3:31 pm   #52
G6ONEDave
Octode
 
G6ONEDave's Avatar
 
Join Date: Dec 2019
Location: Owston Ferry, North Lincolnshire, UK.
Posts: 1,689
Default Re: Samsung 3 band radio cassette, model: STF55L

Hi Malcolm, Strange that the resistance readings are changing, as they should remain static unless there is an electrolytic capacitor involved, which there is not in that part of the circuit. Silly question but the power was off when you did these resistance readings? Also remember not to touch the metal of the probes whilst measuring ohms otherwise you'll measure your body resistance in parallel with the component being tested.

If the power was off next unsolder one end of C2 and check C2 on ohms to check for a short, it should read open circuit on ohms. After that do the same ohms test on C11 having removed one end from the pcb, this again should be open circuit. Now do this same ohms test on C4, which again should read as an open circuit. If any of those capacitors read as a zero ohms then that is the fault. Be careful not to short the meter probes as these capacitors are physically rather small.

Next if these capacitors are all OK the fault is one of 2 items, so first unsolder pin 2 of IC1, making sure that the pin is not touching the pcb tracking, measure on ohms between pin 2 and earth, the reading might be a few ohms but again not a short circuit. If it is a short circuit then it's IC1 which is faulty. If IC1 checks to be OK then you are left with VC1 the Variable tuning capacitor and TC1 which is a preset capacitor that is part of VC1. TC1 is the preset on top of VC1 nearest to L2 on the component side of the pcb.

I sincerely hope that it's not TC1 on the variable tuning capacitor, as finding a replacement tuning capacitor will be like finding the proverbial rocking horse manure. VC1 can be checked for being short circuit as well but will be difficult to unsolder the pin to clear it from the track. The VC1 pin is the one that goes to L1, which is near to the edge of the pcb where the jack sockets arre mounted further along. If you do manage to unsolder this pin and clear it from the track then measure it on ohms, probes between this pin and earth (metal body of the switch will do for earth). If you are unlucky you'll get a low ohms reading that possibly varies, if you do then that is the faulty component.

Let me know your findings.

Dave
__________________
Quote "All is hyperthetical, until it isn't!" (President Laura Roslin, Battlestar Galactica)
G6ONEDave is offline  
Old 1st Jul 2022, 4:25 pm   #53
Formby Mal
Tetrode
 
Join Date: Mar 2022
Location: Southport, Merseyside, UK.
Posts: 59
Default Re: Samsung 3 band radio cassette, model: STF55L

Hi Dave… OK, I’ll have a go. I have some desoldering braid shall I use that with a fine point on the soldering iron and does it matter what end I unsolder also do I solder them back after? When you say “open circuit” is that the same as 0 ohms and again I assume I put the black and red leads either end to test for ohms? Getting very technical now isn’t it….(sweat dripping of my brow).

Cheers Dave.... Malcolm.
Formby Mal is offline  
Old 1st Jul 2022, 4:39 pm   #54
G6ONEDave
Octode
 
G6ONEDave's Avatar
 
Join Date: Dec 2019
Location: Owston Ferry, North Lincolnshire, UK.
Posts: 1,689
Default Re: Samsung 3 band radio cassette, model: STF55L

Yes Malcolm, Sorry if it's getting a bit technical but this is the nature of the beast. Yes you are using both meter probes across each of the components under test, apart from where directed otherwise. De-solder braid is fine for the job, the main thing is to have enough but not too much heat to melt the solder into the braid. Too much heat might cause damage to an otherwise working component. Once you've removed the excess solder, let the capacitors cool down again. Then try moving each capacitor sideways one way and back again to check that the desoldered leg is free from the pcb, if not try a bit of heat on the leg whilst moving the capacitor. This should make the capacitor part company with the pcb tracks.

Something else that I should have mentioned to you is to be extra careful around that tuning capacitor as you might melt the plastic pulley and or the drive cord, both to be avoided. You can tape the cord to the pulley of VC1 before removing the pulley for better access and then move the pulley and cord well out of the way. At least you have the service manual when the time comes to restring it.

I have a nasty feeling about the which component is fauly but we'll worry about that once it's confirmed.

Dave
__________________
Quote "All is hyperthetical, until it isn't!" (President Laura Roslin, Battlestar Galactica)
G6ONEDave is offline  
Old 1st Jul 2022, 7:12 pm   #55
Formby Mal
Tetrode
 
Join Date: Mar 2022
Location: Southport, Merseyside, UK.
Posts: 59
Default Re: Samsung 3 band radio cassette, model: STF55L

Thanks Dave.... wish me luck...
Formby Mal is offline  
Old 2nd Jul 2022, 10:15 am   #56
G6ONEDave
Octode
 
G6ONEDave's Avatar
 
Join Date: Dec 2019
Location: Owston Ferry, North Lincolnshire, UK.
Posts: 1,689
Default Re: Samsung 3 band radio cassette, model: STF55L

Hi Malcolm, Take your time and don't rush it.

When the de-solder wick gets full of solder to a length of about 1/2", cut that bit off but leave a small end section that still has some solder in it (about 1/16"). Doing this will help to keep the applied heat down. Remember that the wick is generally copper braid and as such it gets hot, so don't burn your fingers. You may need repeated tries to remove the solder, it depends on how much there is.

If after doing this component checking you find that TC1/VC1 is the culprit, don't despair too much, there is a possible fix but I'll do a new thread for that outcome under components.

Dave
__________________
Quote "All is hyperthetical, until it isn't!" (President Laura Roslin, Battlestar Galactica)
G6ONEDave is offline  
Old 2nd Jul 2022, 1:21 pm   #57
Formby Mal
Tetrode
 
Join Date: Mar 2022
Location: Southport, Merseyside, UK.
Posts: 59
Default Re: Samsung 3 band radio cassette, model: STF55L

Thanks Dave I did take my time...Well…. I’ve had some fun this morning. I managed to do checks you asked for and C2, C11, C4 and pin 2 of IC1 all showed 1 and no 0 with the ohms test... 1 is what the meter showed at the beginning just switched on. All 4 tests showed ohms before unsoldering and after resoldering back. BUT… I did find a crack in the PCB board, just where the black plastic mount with screw is (see attached pix) which on the track side showed a break in the copper track which affected PR1 on the track side, so I soldered the crack, (is that OK?) see pix attached, is it worth doing the PR1 tests again
I could not find the TC1 and VC1 but is the VC1 the big square plastic box with a blue wire going to C101 (see attached pix) ? It is the only part that is close to L2 and I couldn't see L1 anywhere.

Thanks Dave for your continued help and support…. Malcolm.
Attached Thumbnails
Click image for larger version

Name:	Cracked PCB component side.jpg
Views:	44
Size:	104.3 KB
ID:	260255   Click image for larger version

Name:	Cracked PCB track side.jpg
Views:	39
Size:	99.9 KB
ID:	260256   Click image for larger version

Name:	TC1      VC1.jpg
Views:	38
Size:	148.1 KB
ID:	260257  
Formby Mal is offline  
Old 2nd Jul 2022, 2:00 pm   #58
Formby Mal
Tetrode
 
Join Date: Mar 2022
Location: Southport, Merseyside, UK.
Posts: 59
Default Re: Samsung 3 band radio cassette, model: STF55L

Hi Dave, I did the PR1 volt test again and it's the same: Top 0 volts and bottom 5.18volts. Perhaps I didn't clean the copper track enough if the reason for 0 volts if the broken copper track. The ohms test was the same...both top and bottom were high readings.
Cheers... Malcolm.
Formby Mal is offline  
Old 2nd Jul 2022, 4:18 pm   #59
Formby Mal
Tetrode
 
Join Date: Mar 2022
Location: Southport, Merseyside, UK.
Posts: 59
Default Re: Samsung 3 band radio cassette, model: STF55L

Just found L1 but still can't see TC1 & VC1... Malcolm.
Formby Mal is offline  
Old 2nd Jul 2022, 4:19 pm   #60
G6ONEDave
Octode
 
G6ONEDave's Avatar
 
Join Date: Dec 2019
Location: Owston Ferry, North Lincolnshire, UK.
Posts: 1,689
Default Re: Samsung 3 band radio cassette, model: STF55L

Hi Malcolm,
PR1 still has a crack on the component side of the pcb, that silver line is actually a circuit track. The first thing to do with a cracked pcb is to glue the crack back together, super glue or similar is good for that. Once the glue has dried, you then need to scrape some of the varnish from the track either side of the crack and solder a wire across it. This will give extra support and prevent the solder bridge from cracking. Do the same for all cracked print in this area.

After that you have a couple of options re the cracked silver track on the component side. You can either use silver loaded paint to fill the fine gap and re-complete the circuit either side of the crack, or you will have to replace PR1 with a 1/4w 330 ohm resistor and some thin insulated wiring. these will have to be soldered on the under side where all the soldered tracks are. The idea is to replicate and replace the damaged part of the circuit with a functional one.

The 0 on the meter with the probes touching each other represent a short or zero ohms. The 1 displayed on the meter represents an open circuit, as in the probes not touching themselves or anything else. Any reading between 0 and 1 is the resistance that we are testing for.

VC1 is that square block with the half round tuning pulley screwed to it. VC1 is part of VC1 and is the small screw in the middle of VC1's side nearest to C7. The pin of VC1 to unsolder is in the corner nearest to C4. You might be able to get to it with that half pulley turned to reveal that corner of the VC1 from the print side of the track.

Hope that all makes sense to you. I'll check back later today or tomorrow morn for your update.

Dave
__________________
Quote "All is hyperthetical, until it isn't!" (President Laura Roslin, Battlestar Galactica)
G6ONEDave is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 7:09 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.