Dynatron SRX20 FM not working - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Whitespin · 13th Apr 2010, 5:21 pm

Hello
Sorry to be a pest but I seem to have lost my experts just when it was getting interesting. I've not upset someone with my joke about the Aerial have I?.... I can do worse than that if I try. I do understand that some people have other things to do unlike us geriatrics out here.

Cheers

John

Maestro Maker · 14th Apr 2010, 4:16 pm

Hi John,

If you have 26.9 volts on R431 that is near enough!
No volts on R429 & R438 could mean you are measuring without the FM button pressed?
Anyway, look for the origin of the 15.4 volts supply coming from voltage regulator TR261/R261 in the power supply section at top right hand end of the cicuit diagram. These components are not on the tuner board. [on this schematic all Tunerboard components are 400 series; Audioboard components are 200 series; Controls and off board bits are 600; etc. so indicating their location]
I am visiting family in Devon so can't be of more use until next week; my memory from 25 years ago is very poor without the paperwork!!

Cheers
MM

Whitespin · 14th Apr 2010, 5:22 pm

Sorry to interrupt your holiday my problems can wait till it is convenient for you.
My memory fades after 25 minutes. Incidently the FM button is pressed.

Cheers

John

Whitespin · 20th Apr 2010, 2:23 pm

Well the radiogram has now taken over the spare room. I've removed the radio from the woodwork so everything is more or less accessible. But it will have to remain there for the next couple of weeks because we are off on our hols, fortunately we go by ferry because of the vast amount of camera equipment so we are not affected by the volcano, we hope.

Hopefully by the time we return my expert instructors, who are heroically assisting me will also be at hand to continue the problem solving.

Cheers

John

Maestro Maker · 20th Apr 2010, 5:44 pm

Hi John
Have a good holiday and we shall continue on your return!
Cheers
MM

Whitespin · 19th May 2010, 12:02 am

Well I'm back all refreshed from my hols, just about up to date with all my other commitments. All I need now is my expert, Maestro Maker, to continue with the fault finding on my Dynatron SRX20

Cheers John

Whitespin · 22nd May 2010, 5:50 pm

Hi
It appears that my guru, Maestro Maker is not currently available. Since the circuit diagrams for this model are attached to one of the posts is it possible for one of the many other knowledgeable people on the site to take over guiding me through the fault finding procedure and if possible the repair of my Dynatron

Regards

John

Maestro Maker · 23rd May 2010, 11:42 am

Hi John!

Three more sheets of data for you.
Cheers
MM

Whitespin · 23rd May 2010, 10:52 pm

Thanks MM I have now got 5 sheets of diagrams and will await further instructions.

Cheers

John

Whitespin · 29th Jun 2010, 11:27 pm

I have not been able to make any progress in finding and then hopefully repairing the fault with the FM tuner in my Dynatron radiogram for over a month now. Maestro Maker who was assisting me in the fault finding and has supplied me with all the circuit diagrams has not been on the site for over a month.

I am a novice and would need detailed instructions but I'm keen to learn. Is there a knowledgeable person out there who could help me with this project.

Cheers

Whitespin

Sideband · 29th Jun 2010, 11:38 pm

As a very quick check, make sure that the FM button is actually switching ok. It switches voltage so you should be able to measure DC on both sides of it. If you can't, try shorting the two contacts across. If FM comes to life, you have your fault! Maybe a good clean will sort it.

SB

Whitespin · 2nd Jul 2010, 11:46 am

Thanks SB, my new multimeter has arrived so I will check that out tonight.

Cheers

Whitespin

Whitespin · 5th Jul 2010, 9:26 pm

Hi SM I've done as you suggest and found 25volts on first pin of the FM switch where the yellow wire from TR261/R261 comes in. The switch consists of the body with 2 rows of 6 pins soldered to board B. There is no voltage at the other side of the switch on any of the pins. Question are all the pins in use and which pin do I short the live pin to?

Cheers

Whitespin

Sideband · 5th Jul 2010, 10:47 pm

The circuit doesn't show a layout for the switches. A spot of detective work is therefore required. See if you can find R429 (470 ohm). This should connect directly to the switched 15V supply...in other words, the other end of the switch. If there is no voltage here but there is voltage on the 'live' end of the switch then it seems the switch is duff. Just short the two points together (with the switch pressed in of course). Take care to short the right points...double and triple check. With luck, FM may start working. The switch may respond to switch cleaner. If not, there may be a pair of unused contacts you can use.

SB

Whitespin · 6th Jul 2010, 9:01 pm

I found R429 and there is no voltage there. The 1st pin on the switch doesn't appear to be connected but gives 25volt the 2nd pin is the one with the wire to it and gives 25volt. As said before none of the pins on the other side show any voltage. The next switch is the AM switch this works and gives 25volt both sides of pin 1&2 when on. and the AM side works fine. All these switches terminate at the edge of the board on a double row of numbered pins with wiring looms attached. These go out to other boards. It is possible to trace the printed circuit from the switch pins to the terminals.

Two issues a) Is the voltage ok at 25volts b) what are the risks involved if I put 25volts to the wrong component.

Cheers

Whitespin

Sideband · 6th Jul 2010, 9:23 pm

Well if there is no voltage at R429, I would be inclined to use a piece of wire and temporarily connect it between R429 and the 25 volt supply. It may be a misprint on the circuit and showing 15 rather than 25. I'd use a 470 ohm resistor at about 1 watt rather than a direct connection just to try.

Without a diagram of the switches, it's difficult to work things out but next move would be to remove the complete switch PCB and use a meter to try and work out what should switch what. You could trace the 15 (25?) volts back to source in case a regulator has gone short-circuit.

SB

Whitespin · 6th Jul 2010, 11:02 pm

Thanks I have bought some resistors off eBay will give it a try when they arrive.

Whitespin

Sideband · 6th Jul 2010, 11:44 pm

TR261 over on the power supply is a simple series regulator transistor. If that's gone short, you'll get 25V on the 15V rail

. I'd check on that transistor first. There should be 25V on the collector and around 15V on the emitter. There's a 16V zener diode from the base down to chassis...that's also worth a check...may be open circuit.

SB

Whitespin · 9th Jul 2010, 12:54 pm

Unfortunately whilst checking the voltages on TR261 I've shorted it out and it is now dead.
Prior to that I was getting 26V and 17V directly off the transistor legs but 26V all round on the solder side. Is it possible to get a replacement for TR261?

Whitespin

Mark the Mender · 9th Jul 2010, 8:37 pm

TR 261 is an MA8003, towers shows an equivalent of a BFY50, if you are sure it is the transistor is fried.

Chris Treadwell at Mode components www.modecomponents.co.uk has some in stock.

no connection etc just a customer

cheers Mark

13th Apr 2010, 5:21 pm	#21
Whitespin Retired Dormant Member Join Date: Apr 2010 Location: Doncaster, South Yorkshire, UK. Posts: 27	Re: Dynatron SRX20 FM not working Hello Sorry to be a pest but I seem to have lost my experts just when it was getting interesting. I've not upset someone with my joke about the Aerial have I?.... I can do worse than that if I try. I do understand that some people have other things to do unlike us geriatrics out here. Cheers John

14th Apr 2010, 4:16 pm	#22
Maestro Maker Retired Dormant Member Join Date: Feb 2010 Location: South Cambridgeshire, UK. Posts: 99	Re: Dynatron SRX20 FM not working Hi John, If you have 26.9 volts on R431 that is near enough! No volts on R429 & R438 could mean you are measuring without the FM button pressed? Anyway, look for the origin of the 15.4 volts supply coming from voltage regulator TR261/R261 in the power supply section at top right hand end of the cicuit diagram. These components are not on the tuner board. [on this schematic all Tunerboard components are 400 series; Audioboard components are 200 series; Controls and off board bits are 600; etc. so indicating their location] I am visiting family in Devon so can't be of more use until next week; my memory from 25 years ago is very poor without the paperwork!! Cheers MM

14th Apr 2010, 5:22 pm	#23
Whitespin Retired Dormant Member Join Date: Apr 2010 Location: Doncaster, South Yorkshire, UK. Posts: 27	Re: Dynatron SRX20 FM not working Sorry to interrupt your holiday my problems can wait till it is convenient for you. My memory fades after 25 minutes. Incidently the FM button is pressed. Cheers John

20th Apr 2010, 2:23 pm	#24
Whitespin Retired Dormant Member Join Date: Apr 2010 Location: Doncaster, South Yorkshire, UK. Posts: 27	Re: Dynatron SRX20 FM not working Well the radiogram has now taken over the spare room. I've removed the radio from the woodwork so everything is more or less accessible. But it will have to remain there for the next couple of weeks because we are off on our hols, fortunately we go by ferry because of the vast amount of camera equipment so we are not affected by the volcano, we hope. Hopefully by the time we return my expert instructors, who are heroically assisting me will also be at hand to continue the problem solving. Cheers John

20th Apr 2010, 5:44 pm	#25
Maestro Maker Retired Dormant Member Join Date: Feb 2010 Location: South Cambridgeshire, UK. Posts: 99	Re: Dynatron SRX20 FM not working Hi John Have a good holiday and we shall continue on your return! Cheers MM

19th May 2010, 12:02 am	#26
Whitespin Retired Dormant Member Join Date: Apr 2010 Location: Doncaster, South Yorkshire, UK. Posts: 27	Re: Dynatron SRX20 FM not working Well I'm back all refreshed from my hols, just about up to date with all my other commitments. All I need now is my expert, Maestro Maker, to continue with the fault finding on my Dynatron SRX20 Cheers John

22nd May 2010, 5:50 pm	#27
Whitespin Retired Dormant Member Join Date: Apr 2010 Location: Doncaster, South Yorkshire, UK. Posts: 27	Re: Dynatron SRX20 FM not working Hi It appears that my guru, Maestro Maker is not currently available. Since the circuit diagrams for this model are attached to one of the posts is it possible for one of the many other knowledgeable people on the site to take over guiding me through the fault finding procedure and if possible the repair of my Dynatron Regards John

23rd May 2010, 10:52 pm	#29
Whitespin Retired Dormant Member Join Date: Apr 2010 Location: Doncaster, South Yorkshire, UK. Posts: 27	Re: Dynatron SRX20 FM not working Thanks MM I have now got 5 sheets of diagrams and will await further instructions. Cheers John

29th Jun 2010, 11:27 pm	#30
Whitespin Retired Dormant Member Join Date: Apr 2010 Location: Doncaster, South Yorkshire, UK. Posts: 27	Re: Dynatron SRX20 FM not working I have not been able to make any progress in finding and then hopefully repairing the fault with the FM tuner in my Dynatron radiogram for over a month now. Maestro Maker who was assisting me in the fault finding and has supplied me with all the circuit diagrams has not been on the site for over a month. I am a novice and would need detailed instructions but I'm keen to learn. Is there a knowledgeable person out there who could help me with this project. Cheers Whitespin

29th Jun 2010, 11:38 pm	#31
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,580	Re: Dynatron SRX20 FM not working As a very quick check, make sure that the FM button is actually switching ok. It switches voltage so you should be able to measure DC on both sides of it. If you can't, try shorting the two contacts across. If FM comes to life, you have your fault! Maybe a good clean will sort it. SB __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

2nd Jul 2010, 11:46 am	#32
Whitespin Retired Dormant Member Join Date: Apr 2010 Location: Doncaster, South Yorkshire, UK. Posts: 27	Re: Dynatron SRX20 FM not working Thanks SB, my new multimeter has arrived so I will check that out tonight. Cheers Whitespin

5th Jul 2010, 9:26 pm	#33
Whitespin Retired Dormant Member Join Date: Apr 2010 Location: Doncaster, South Yorkshire, UK. Posts: 27	Re: Dynatron SRX20 FM not working Hi SM I've done as you suggest and found 25volts on first pin of the FM switch where the yellow wire from TR261/R261 comes in. The switch consists of the body with 2 rows of 6 pins soldered to board B. There is no voltage at the other side of the switch on any of the pins. Question are all the pins in use and which pin do I short the live pin to? Cheers Whitespin

5th Jul 2010, 10:47 pm	#34
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,580	Re: Dynatron SRX20 FM not working The circuit doesn't show a layout for the switches. A spot of detective work is therefore required. See if you can find R429 (470 ohm). This should connect directly to the switched 15V supply...in other words, the other end of the switch. If there is no voltage here but there is voltage on the 'live' end of the switch then it seems the switch is duff. Just short the two points together (with the switch pressed in of course). Take care to short the right points...double and triple check. With luck, FM may start working. The switch may respond to switch cleaner. If not, there may be a pair of unused contacts you can use. SB __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

6th Jul 2010, 9:01 pm	#35
Whitespin Retired Dormant Member Join Date: Apr 2010 Location: Doncaster, South Yorkshire, UK. Posts: 27	Re: Dynatron SRX20 FM not working I found R429 and there is no voltage there. The 1st pin on the switch doesn't appear to be connected but gives 25volt the 2nd pin is the one with the wire to it and gives 25volt. As said before none of the pins on the other side show any voltage. The next switch is the AM switch this works and gives 25volt both sides of pin 1&2 when on. and the AM side works fine. All these switches terminate at the edge of the board on a double row of numbered pins with wiring looms attached. These go out to other boards. It is possible to trace the printed circuit from the switch pins to the terminals. Two issues a) Is the voltage ok at 25volts b) what are the risks involved if I put 25volts to the wrong component. Cheers Whitespin

6th Jul 2010, 9:23 pm	#36
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,580	Re: Dynatron SRX20 FM not working Well if there is no voltage at R429, I would be inclined to use a piece of wire and temporarily connect it between R429 and the 25 volt supply. It may be a misprint on the circuit and showing 15 rather than 25. I'd use a 470 ohm resistor at about 1 watt rather than a direct connection just to try. Without a diagram of the switches, it's difficult to work things out but next move would be to remove the complete switch PCB and use a meter to try and work out what should switch what. You could trace the 15 (25?) volts back to source in case a regulator has gone short-circuit. SB __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

6th Jul 2010, 11:02 pm	#37
Whitespin Retired Dormant Member Join Date: Apr 2010 Location: Doncaster, South Yorkshire, UK. Posts: 27	Re: Dynatron SRX20 FM not working Thanks I have bought some resistors off eBay will give it a try when they arrive. Whitespin

6th Jul 2010, 11:44 pm	#38
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,580	Re: Dynatron SRX20 FM not working TR261 over on the power supply is a simple series regulator transistor. If that's gone short, you'll get 25V on the 15V rail . I'd check on that transistor first. There should be 25V on the collector and around 15V on the emitter. There's a 16V zener diode from the base down to chassis...that's also worth a check...may be open circuit. SB __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

9th Jul 2010, 12:54 pm	#39
Whitespin Retired Dormant Member Join Date: Apr 2010 Location: Doncaster, South Yorkshire, UK. Posts: 27	Re: Dynatron SRX20 FM not working Unfortunately whilst checking the voltages on TR261 I've shorted it out and it is now dead. Prior to that I was getting 26V and 17V directly off the transistor legs but 26V all round on the solder side. Is it possible to get a replacement for TR261? Whitespin

9th Jul 2010, 8:37 pm	#40
Mark the Mender Retired Dormant Member Join Date: Apr 2008 Location: Warrington, Cheshire, UK. Posts: 421	Re: Dynatron SRX20 FM not working TR 261 is an MA8003, towers shows an equivalent of a BFY50, if you are sure it is the transistor is fried. Chris Treadwell at Mode components www.modecomponents.co.uk has some in stock. no connection etc just a customer cheers Mark