A77 Optical Sensor - UK Vintage Radio Repair and Restoration Discussion Forum

Linnovice · 21st Apr 2016, 8:03 pm

Hi all, a quick request for advice. I'm in the process of refurbishing a nice Revox A77 1/4 Track machine. All is going well and I'm gradually working through changing the capacitors. I have discovered that the end of tape shut off sensor is not working. In a box of spare bits I've bought with the machine there is a replacement optical sensor. Unfortunately it does not have the two wires connected to it, I will have to use the ones off of the one I'm replacing. In the service manual it states not to solder them as the sensor is heat sensitive. The spare I have has obviously been desoldered so it must be possible.
My question is this. Are there any tricks, advice or trade secrets in soldering parts such as these? It must be possible as the existing one on the machine has soldered connections.
Mike

Ted Kendall · 21st Apr 2016, 8:11 pm

Usual trick is to put a heat sink between the solder joint and the component - somewhere I have a very neat pair of ali reverse tweezers which work a treat, but a pair of long-nosed pliers would do just as well.

julie_m · 21st Apr 2016, 9:43 pm

With good technique and a thermostatic iron fitted with the appropriate sized tip, it's possible to solder most things without overheating them.

When I put a new thermal fuse (obviously temperature-sensitive) in an electric heater, I first cleaned the leads thoroughly, so the solder would take easily; doused the body with freezer spray, gripped the lead with pliers and soldered it as quickly as I dared; and let the whole thing cool down before doing the other lead.

It held; but I'll bet it wouldn't have, if I had bought only one replacement thermal fuse and not a pack of five .....

Linnovice · 21st Apr 2016, 10:06 pm

Hmmm, I like your style but I've only got one optical sensor �� . . .

dseymo1 · 22nd Apr 2016, 3:39 am

The link given in post no.3 in this thread might prove helpful.

Diabolical Artificer · 22nd Apr 2016, 6:38 am

A croc clip, bulldog clip etc works as a heatsink and using a hot iron and flux helps too. It's about dwell time Mike, IE how long your iron is on the component. With a good hot iron, and a bit of preparation and forethought it's pretty straight forward, same as soldering batteries. See this video ..... at around 24:00 https://www.youtube.com/watch?v=HqsXe3IKTCo for how to solder batteries, perhaps you could practice on a few dead ones to get your technique down first?

Andy.

21st Apr 2016, 8:03 pm	#1
Linnovice Hexode Join Date: Jun 2014 Location: Chelmsford, Essex, UK Posts: 386	A77 Optical Sensor Hi all, a quick request for advice. I'm in the process of refurbishing a nice Revox A77 1/4 Track machine. All is going well and I'm gradually working through changing the capacitors. I have discovered that the end of tape shut off sensor is not working. In a box of spare bits I've bought with the machine there is a replacement optical sensor. Unfortunately it does not have the two wires connected to it, I will have to use the ones off of the one I'm replacing. In the service manual it states not to solder them as the sensor is heat sensitive. The spare I have has obviously been desoldered so it must be possible. My question is this. Are there any tricks, advice or trade secrets in soldering parts such as these? It must be possible as the existing one on the machine has soldered connections. Mike __________________ Small Scotch, New Aids and Happy Ears

21st Apr 2016, 8:11 pm	#2
Ted Kendall Dekatron Join Date: Jul 2008 Location: Kington, Herefordshire, UK. Posts: 3,670	Re: A77 Optical Sensor Usual trick is to put a heat sink between the solder joint and the component - somewhere I have a very neat pair of ali reverse tweezers which work a treat, but a pair of long-nosed pliers would do just as well.

21st Apr 2016, 9:43 pm	#3
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: A77 Optical Sensor With good technique and a thermostatic iron fitted with the appropriate sized tip, it's possible to solder most things without overheating them. When I put a new thermal fuse (obviously temperature-sensitive) in an electric heater, I first cleaned the leads thoroughly, so the solder would take easily; doused the body with freezer spray, gripped the lead with pliers and soldered it as quickly as I dared; and let the whole thing cool down before doing the other lead. It held; but I'll bet it wouldn't have, if I had bought only one replacement thermal fuse and not a pack of five ..... __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

21st Apr 2016, 10:06 pm	#4
Linnovice Hexode Join Date: Jun 2014 Location: Chelmsford, Essex, UK Posts: 386	Re: A77 Optical Sensor Hmmm, I like your style but I've only got one optical sensor �� . . . __________________ Small Scotch, New Aids and Happy Ears

22nd Apr 2016, 3:39 am	#5
dseymo1 Retired Dormant Member Join Date: Dec 2007 Location: Shropshire, UK. Posts: 3,051	Re: A77 Optical Sensor The link given in post no.3 in this thread might prove helpful.

22nd Apr 2016, 6:38 am	#6
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,658	Re: A77 Optical Sensor A croc clip, bulldog clip etc works as a heatsink and using a hot iron and flux helps too. It's about dwell time Mike, IE how long your iron is on the component. With a good hot iron, and a bit of preparation and forethought it's pretty straight forward, same as soldering batteries. See this video ..... at around 24:00 https://www.youtube.com/watch?v=HqsXe3IKTCo for how to solder batteries, perhaps you could practice on a few dead ones to get your technique down first? Andy. __________________ Curiosity hasn't killed this cat...so far.