Ok, so they automated it, at least some.  The negative supply to the display should not be adjusted from what I know, the contrast is a separate line. Looking at the display's data sheet, the -VEE

The old display has no pot on it. Measurements I've made suggest the THS720P adjusts the contrast by varing the negative supply to the display. I do see some change in the display as I vary the

That's an STN display.  All the ones that I've ever seen have a contrast adjustment, generally a variable voltage.  For graphics displays I think it was a negative voltage, for the little 7 segment

I am still fighting with my replacement LCD display. My latest theory is per the Sharp spec the display expects a contrast pot between pin 11 and pin 12 of the interface. From the THS700 service

The reason I'm replacing the display is the LCD panel has delaminated, or something of that sort. I too have successfully replaced CCFLs with LCDs on some units.

I do something similar, but since I'm doing battery operated equipment where the highest desired voltage is 5.0 volts, I use an individual dropping resistor per LED.  Definitely not the most

I have repaired a whole bunch of displays in marine equipment using led strips. These a usually segments of three leds in series with a small resister. Then it's "rinse and re[eat" to the next

Hi, Love to hear more about what you did to replace the displays. Many thanks, John aka DBN

Ok, interleaved: And there's the first problem.  I'm using the 468 power supply (ought to be close) as a reference.  Bridge rectifiers can be used two ways, one is a full wave bridge.  The +5 volt

Thanks EJP and Dave now I am more confused my manual which matches my later SN has all the test points for both units and shows two different PCBs its the early SN unit that does not match the manual

Thanks Roger, Your advice was very useful and eventually indirectly led me to solving the problem! The HV at its test point was constant and about 1.3% high at 3 KV which I decided to accept but when

I replaced the CCFL in two THS720's with LED's. It makes an enormous improvement. Its not hard but it is a little involved. You will need a step up inverter and a backlight regulator. LED strips can

Albert, PF, Hopefully I will be able to make more measurements today. Sorry if I’ve been responding a bit later lately. Family issues.

Hi Harvey. As the scope was essentially dead with only 0.6v at the test points on the 15v, 5v, -8v and -15v rails with 38 and 43 volts on the 140 and 65v test points respectively with no lights,

Jeff U410 changed from a "Tektronix Selected part" to a Motorola Part MC1436CG at serial B130000.  . The "Tektronix selected part" may have been a Motorola part as well that was sorted for some

Manual states U410 is Tek part no 156-0400-00, and the cross reference gives Motorola part no MC1436CG, a high voltage (+-30V) 1MHz 94dB op-amp. EJP

you have a number of linear supplies:  transformer secondary driving bridge which is hooked up to the main filter capacitor, there is, in normal power supply design theory, no way to get voltage at

Looks like they didn't include those on the upper JFET's gate - just capacitively-coupled through a 12pF cap to the upper FET's gate. Thanks, Barry - N4BUQ

Hi all, last update for the evening. I didn't quite do as planned as forgot about the 65v and 140v bridge CR1721 and started from the 15v bridge instead. But hey, that gave out 17v, and the fan

Those diodes are then to protect the IC, not the JFETs. There should be one more clamp, possibly two, at the front end to protect the upper JFET's gate. Ed