Dynatron SRX20 Thermal Fuse - UK Vintage Radio Repair and Restoration Discussion Forum

ilancuk · 18th Feb 2019, 9:48 am

I am restoring a Dynatron SRX20 music centre. It appears to be dead. The 240V supply to the transformer is OK so I suspect it is the thermal fuse. Does anyone know the location and rating of this fuse?

Station X · 18th Feb 2019, 9:57 am

Hello and welcome to the forums.

The circuit diagram can be found in this thread:-

https://www.vintage-radio.net/forum/...ad.php?t=52606

The thermal fuse is wired into the live side of the mains supply between the connector block and the transformer. Unfortunately I don't know its physical location or rating. If you can locate it, any marking on it may give a clue.

If power is reaching the transformer, it's possible the fuse is embedded in the windings.

Nuvistor · 18th Feb 2019, 10:15 am

Dynatron like Pye used the Philips type of embedded fuse in the transformer in some units. The fuse slides into a slot within the transformer windings and is easy to replace, if they are available.

They don’t usually just fail, there will be a reason, S/C rectifier?

ilancuk · 19th Feb 2019, 3:46 pm

I have found the fuse and replaced it. The tape deck now powers up, but the receiver is still dead - the lights don’t even come on - any ideas? There does seem to be some voltage at plug 101.

Station X · 19th Feb 2019, 3:56 pm

Quote:

Originally Posted by ilancuk

There does seem to be some voltage at plug 101.

That's a pretty vague statement.

Your first move should be to use your meter to check that all DC power supply voltages are present and correct.

ilancuk · 20th Feb 2019, 3:53 pm

Thank you and sorry for the vagueness.

Am I correct that my meter should read:

25v across pins 1 and 6 (black/yellow)
36v across pins 2 and 3 (pink/pink)
6.3v across pins 4 and 5 (brown/brown)

Station X · 24th Feb 2019, 12:04 pm

Sorry, but I can't help you with that one apart from pins 4 and 5 (brown wires) which should have 6.3V AC across them. This voltage powers the lamps so, if the voltage is present and they're not lighting up you have a problem with F603 or the lamps themselves.

Check DC voltages at convenient points for example:-

Chassis to C602 and C603 for the 18VDC supplies.
Chassis to C604 for the 25VDC supply.
Chassis to C262 for the 16VDC supply.
Chassis to R262 for the 15.4VDC supply.

Station X · 27th Apr 2019, 7:50 pm

I guess the OP gave up on this?

18th Feb 2019, 9:48 am	#1
ilancuk Retired Dormant Member Join Date: Feb 2019 Location: Truro, Cornwall, UK. Posts: 3	Dynatron SRX20 Thermal Fuse I am restoring a Dynatron SRX20 music centre. It appears to be dead. The 240V supply to the transformer is OK so I suspect it is the thermal fuse. Does anyone know the location and rating of this fuse?

18th Feb 2019, 9:57 am	#2
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Dynatron SRX20 Thermal Fuse Hello and welcome to the forums. The circuit diagram can be found in this thread:- https://www.vintage-radio.net/forum/...ad.php?t=52606 The thermal fuse is wired into the live side of the mains supply between the connector block and the transformer. Unfortunately I don't know its physical location or rating. If you can locate it, any marking on it may give a clue. If power is reaching the transformer, it's possible the fuse is embedded in the windings. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

18th Feb 2019, 10:15 am	#3
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: Dynatron SRX20 Thermal Fuse Dynatron like Pye used the Philips type of embedded fuse in the transformer in some units. The fuse slides into a slot within the transformer windings and is easy to replace, if they are available. They don’t usually just fail, there will be a reason, S/C rectifier? __________________ Frank

19th Feb 2019, 3:46 pm	#4
ilancuk Retired Dormant Member Join Date: Feb 2019 Location: Truro, Cornwall, UK. Posts: 3	Re: Dynatron SRX20 Thermal Fuse I have found the fuse and replaced it. The tape deck now powers up, but the receiver is still dead - the lights don’t even come on - any ideas? There does seem to be some voltage at plug 101.

20th Feb 2019, 3:53 pm	#6
ilancuk Retired Dormant Member Join Date: Feb 2019 Location: Truro, Cornwall, UK. Posts: 3	Re: Dynatron SRX20 Thermal Fuse Thank you and sorry for the vagueness. Am I correct that my meter should read: 25v across pins 1 and 6 (black/yellow) 36v across pins 2 and 3 (pink/pink) 6.3v across pins 4 and 5 (brown/brown)

24th Feb 2019, 12:04 pm	#7
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Dynatron SRX20 Thermal Fuse Sorry, but I can't help you with that one apart from pins 4 and 5 (brown wires) which should have 6.3V AC across them. This voltage powers the lamps so, if the voltage is present and they're not lighting up you have a problem with F603 or the lamps themselves. Check DC voltages at convenient points for example:- Chassis to C602 and C603 for the 18VDC supplies. Chassis to C604 for the 25VDC supply. Chassis to C262 for the 16VDC supply. Chassis to R262 for the 15.4VDC supply. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

27th Apr 2019, 7:50 pm	#8
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Dynatron SRX20 Thermal Fuse I guess the OP gave up on this? __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.