CurtPalme.com Home Theater Forum

[dvh99]

some info on the p-channel transistors, i used bft93 for q18 to q23 and q25 to q27.

feedback and gain is now 683ohms on the ths3201 i added a 100nf across vdd and vee

[Nashou66]

Add more filtering to those transistor power supply rails too Dennis, just like on the THS3201.

Athanasios

[dvh99]

the pj does sync but when reversing sync from negative to positive i get less of those sloping lines.
could it be that the short on the +5v line damaged the opamp?
i still dont get a picture but i can select source and swap colours 1-2-3.

[dvh99]

nash do you think those 6.8uf tants would be usefull there

[dvh99]

maybe that short took out the ad834 any ideas?

[Nashou66]

Try another THS3201 or EL5166 first.

Athanasios

[mp20748]

[Nashou66]

I think he only has the green channel on the retro board connected for now, the other colors are on the Vim . Right dennis or did you populate the rest of the board?

Athanasios

[dvh99]

all components are on the addon board but only the mini rca connector is on the green channel right now.
i will try another ths3201 or maybe a clc449 known to be working to be sure.

[dvh99]

green is taken right after the sd5401 so thats ok and green contrast is taken from tp15, resistors r46 r97 r131 r167 are removed and the 3 ad835s

vertical blanking is taken ar resistor r46

[dvh99]

i get nothing but noise on the tubeface now, the pj syncs but i think the opamp oscillates.
or is there another thing going on?

[dvh99]

the board works but the opamp oscillates, what resistor values should i use for r263 and r264
i have increased the value from r259 and r270 to 1k.

btw no vsync out of range anymore

[mp20748]

Stay away from the THS3201 for now, or until you get the circuit working properly. It's not a simple solder and play chip..

When doing projects like this always go with known workable chips first. Once everything works out, then try the chips you'd want to go with, but do so trying one stage at a time.

Those above 1Ghz chips are not going to be easy to work with on floating PC boards.


You should put in the CLC449's for now.



Also, once you get everything working, the 2N3906's will be a must for that circuit. The other transistors will work, but the image will not be right. Those transistors in those circuits are not bandwidth critical at all.

[dvh99]

i think thats the best thing to do indeed i raised the gain resistance to 2k4 and it improved a very little bit but nowhere where it should be.
first i am going to replace the bft 93s and then change out the ths3201
i need some caps in the pico range for that opamp but i dont have them i was thinking 10 22 47pf.

[dvh99]

something else is going on
i put in the clc449 but still get lots of oscillation
maybe grounding more might help so that will be next.

[dvh99]

well i am back to stock configuration but it makes no difference.
is it normal that the output voltage at pin6 of the opamps is somewhere around 250-300mv
output of w1 anb w2 is steady at 6.55v

[mp20748]

[dvh99]

dc on a multimeter

[mp20748]

That could be normal. It's just showing a little DC offset.


With a signal on the BNC's, measure on the AD834 pin 8 DC voltage at 30 contrast and also at 70 contrast. Post back with those two voltage readings.

[dvh99]

hi mike i measured these cant remember exactly what the values were but they did change with contrast uop down think it was 3-5 volts or so.

i suspect the board to be of bad design (too long traces) therefore i made another pcb and will test tonight.