Sinclair mtv1

[jr_tech]

For grins, I took the cover off of the VHF tuner... YIKES! brain surgery is correct! Here is what mine looks like:



I have identified the 4 varactor tuning diodes and painted the tops with red paint... the 5 band switching PIN diodes were factory painted yellow (#5 is barely visible under coil next to blue and red top semiconductors)... the RF transistor (barely visible under tan wire and coil) was factory painted white and the oscillator and mixer transistors are painted blue on the tops. Do we agree?

jr

[timmy]

Originally Posted by jr_tech

For grins, I took the cover off of the VHF tuner... YIKES! brain surgery is correct! Here is what mine looks like:



I have identified the 4 varactor tuning diodes and painted the tops with red paint... the 5 band switching PIN diodes were factory painted yellow (#5 is barely visible under coil next to blue and red top semiconductors)... the RF transistor (barely visible under tan wire and coil) was factory painted white and the oscillator and mixer transistors are painted blue on the tops. Do we agree?

jr

yes it looks right although I did see the other diodes and didn't know what they were but you had said there were varactors and pin diodes so what I took out may have been good and it could have even one of the transistors. The tan wire on mine was green corroded and making no contact so I fixed it but made no difference , befor I lost brightness. Well I'll tell you if someone knew these little sets and told me things to change and it would be successful I would probably do it since the only thing I know is the tuner is dead but the brightness problem if it didn't damage the IC next to the line amp pot then it's more likely a ksp44 transistor not a problem but the IC , there is no info on that to change it.

[jr_tech]

This is what I believe is one of the varactor tuning diodes in the Sinclair MTV-1 VHF tuner section (pictured above)... it is in a TO-92 style case with no markings on the flat side, just 3 color bands on the back. (I painted the red on the top for identification in my previous post)



Apparently the tuning voltage in the set can go as high as 31 volts.

Identification and/or substitution recommendations needed.

Thanks,
jr

.

[timmy]

Originally Posted by jr_tech

This is what I believe is one of the varactor tuning diodes in the Sinclair MTV-1 VHF tuner section (pictured above)... it is in a TO-92 style case with no markings on the flat side, just 3 color bands on the back. (I painted the red on the top for identification in my previous post)



Apparently the tuning voltage in the set can go as high as 31 volts.

Identification and/or substitution recommendations needed.

Thanks,
jr

.

Yes your right according to the fellow in England working on this set said in the posts that he too identified those varicaps and could not find replacements and did note that they had 3 colors just as you said. If we had a real schematic that may show values of sorts it may help but it's looking like a dead end for me. Looking at your pic there is green on the components and if that's moved it will probably break off as one of the pin diodes I took out one leg broke but it believe it tested leaking and they are available so that's not a problem . Would you know by the schematic what I possibly burned that killed the brightness and brought down the 45v to 26 volts.

[jr_tech]

Originally Posted by timmy

Would you know by the schematic what I possibly burned that killed the brightness and brought down the 45v to 26 volts.

I can only guess, but is the 3 volt supply still working? (pin 7 on the ic just behind the pots) Is the HV at the ends of the large mylar caps (standing up behind the position pot board) close to 1900 Volts?

jr

[timmy]

I have 3 volts on pin 7 but the hv just bearly gets of the start line of the hv probe. Actually aside from a dark screen the pic was still visible so maybe it's the hv I knocked out.

[jr_tech]

Grasping at straws, I would check/replace the 3 electrolytic cans between the ic and the HV transformer... the surge might have injured them... the diode standing up between two of the cans could be suspect as well as the 4 transistors in the area. A very real possibility is that the regulator circuit on the ic has been damaged. I really can't guess.

jr