Super TGSL With H Bridge TX Diff RX Quad Sampling

[Davor]

The IDX' oscillator has a fixed emitter degeneration resistor of a PNP transistor. It is a handy place to regulate saturation point of this transistor and consequently Tx signal purity. The only thing missing is a trimmer.
It is OK to leave a fixed resistor if you know the optimum value, and in mass production it requires obtaining transistors with narrow tolerance of beta, something that amateurs will never have.

[Silver Dollar]

Looking through the Archives I found this schematic. That might be the TX tweak for IDX;



You adjust it till it touches the rail. That maximizes your TX current and keeps it more stable
(as it has no where to go)...

[hoadlies]

Looking through the Archives I found this schematic. That might be the TX tweak for IDX;

[ATTACH]28838[/ATTACH]

You adjust it till it touches the rail. That maximizes your TX current and keeps it more stable
(as it has no where to go)...

THANKS A lot GUYS,,, I will investigate that issue ,CHEERS BARRY..

[sinclairuser]

Looking through the Archives I found this schematic. That might be the TX tweak for IDX;

[ATTACH]28838[/ATTACH]

You adjust it till it touches the rail. That maximizes your TX current and keeps it more stable
(as it has no where to go)...

thanks for that silverdollar, allways on the lookout for idx mods(for my whites original), its a great machine infact i have a kit of parts for the idx so as to future proof it with this i can repair any fault.
barry if you fancy tinkering with the idx, if you dont have one allready i can recommend the vdi unit i know some build the idx without if you have its a great add on you can build it on perf board as well.

[Silver Dollar]

Here's a mod schematic (for IDX) I found somewhere. Not sure if they all work but some ideas to try?

[sinclairuser]

Here's a mod schematic (for IDX) I found somewhere. Not sure if they all work but some ideas to try?

[ATTACH]28845[/ATTACH]

thanks all ideas gratefully received.

[Silver Dollar]

Well I finished wiring it up today. I'll fire it up tomorrow and see how it works!
I'm a bit worried the minus voltage generator might not like the TX signal as
it is floating a bit off ground. If it doesn't work I'll just throw in a 7660 for the
negative voltage. It only needs a tickle to sync to the TX so should work OK.

[Davor]

I'm seeing a blob of something amber-ish right behind the pad a yellow wire in front is soldered in - is it a soldering paste? I hope it is not. That would explain the previous troubles.
I wouldn't expect problems with negative voltage due to the the Tx because its signal does not pass below the ground. Provided there are no excessive loads in a negative rail. I've seen recently a solution for -5V in RS485 using CD4053 (!). It is very minimalistic.

[Silver Dollar]

That blob is the pad has lifted and is gone now. I had heavy wires for the TX soldered there
and put them on and removed them many times and the pad fell off. I took the board to work
and cleaned it. We have a heated ultrasonic cleaner with flux off in it. It does a good job!

There were flux issues as the board is shipped coated in flux to promote good soldering and
I had cleaned it with alcohol several times but there was still some sticky residue. So I decided
to bring it to work to do a better job. But raising the input level and adding hysteresis was
necessary too.

[Davor]

I have that in mind, and I'll see to boosting level to the limit, and also I'll try to reduce input impedance.

[Silver Dollar]

Well it didn't work. The negative supply didn't come up. I used a 4069 as I didn't have a 40106 and
figured the TX not coming to gnd would make it not work. So I added a 7660 but it didn't work either
maybe there a wiring error. I moved the power connections as they worked better on the other side
of the board and maybe the negative is in the wrong spot I'll have a look tomorrow.

Here's the schematic as it sits today;

[Silver Dollar]

Well I found the problem with the minus voltage. A short had crept in. Now it works
but sounds continuously in PP mode and doesn't sound in Disc mode. Here are some
pictures. I'm not sure how to null the coils...

Pins 1 and 2 of the 4053 - Note Channel 2 is 2v the switch pin broke off my probe...


Pin 15


Pin 4

[dfbowers]

In the schematic TR5 and TR6 have nothing connected to the collectors. Is that an error or does it just turn them into diodes?

[Davor]

I'm not sure how to null the coils...

The coil is either completely out of balance, or you have some other problem there. What kind of coil do you have? Is it still open for corrections? In case it is potted there is a possibility to tune it with a piece of ferrite.
Either way, first you need to see voltage on the coil using a scope without any load. By squeezing, moving or otherwise you bring it to some sort of balance. In case it is a DD coil, at this point you should put some extra insulation between the coils where they touch each other, and put a drop of crazy glue on each side.
Now you can connect your coil to a preamp, and check the preamp output voltage instead.
Check the balance. Now when you obtain balance again, drop some crazy glue a centimetre from the touching points towards the centre. Proceed in the same fashion until you reach near the centre and apply some extra glue on each side, but leave some 5cm at the centre without glue so that you may fine tune your coil. At this point the coils are quite rigid, and you are able only to tweak balance a little bit. It is best not to pot the coil immediately, and just let it set overnight, so that the wires are allowed to relax with the glue. Do the final tuning prior to potting and squeeze it just a bit over the balance point so that the wires relax back towards the balance point. Done.

This way of tuning allows you to avoid extra curls of wire for fine tuning. In case you are not happy with the final result of a potted coil, you can either form a curl of a connecting wire or you can use a small piece of ferrite and find a sweet spot on the coil body that provides a perfect balance, and fix the ferrite there. You'll find that there is always some remaining minimum you can't make any deeper with either curl or a ferrite, and you can make it deeper by finding a sweet spot with a small chip made of a milk carton (very thin aluminium foil is in there).

[Davor]

@dfbowers, yes, those are diodes. They could most probably be replaced by 6.8V zener in forward direction (!) but using a transistor of the same kind provides a better match, and basically they cost the same.