CDM750 TX pwr problem

[Paul]

While reflashing a cdm750, the tuning data were blanked and resulted with a radio that has no tx power.
I tried to retune it with the global tuner, but in vain. No matter what the values of "K & M Tuning" and "PA bias" are.
Any ideas?

[Jim202]

By any chance is this the result of the famous carbon switch on the cover? This may have been covered by
another thread if this is in fact the case.

Jim

While reflashing a cdm750, the tuning data were blanked and resulted with a radio that has no tx power.
I tried to retune it with the global tuner, but in vain. No matter what the values of "K & M Tuning" and "PA bias" are.
Any ideas?

[jackhackett]

Maybe try reading another radio's tuning data and writing that into it.

[Al]

Is the Tx power output really *0*, or some low value such as 400-600 Mw? An indication of a very low value would likely tell you that your PC board has an LDMOS PA vice bipolar, and the LDMOS is very sensitive to complete or partial destruction because the forward gate bias is incorrect(which may have occurred when the bias tuning data was lost). Either way, if you monitor B+ current while the unit is keyed, are you able to slowly adjust the bias and observe a change in the current draw? I suspect not, which would likely indicate that the PA is defective.

[Paul]

Thanks for your ideas guys, but I have some good and some bad news..
(By the way, it is a low band II model)
I removed the board to have a visual check on the underside and discovered all four 10ohm resistors
supplying the driver transistor to be broken and partialy desoldered.
This happened due to high bias current, while I was f**king around bias values. (remember, RTFM?)
I was lucky enough having a blown GM950 board that had exactly four 10 ohm resistors, that replaced
the blown CDM ones. According to the help file, I started to tune the bias current (no bullsh*t this time!)
I was able to set the first two of them but no current on the third no matter the value.
I was also unable to set the #2 DAC and the K&M tuning data.
Any info on why there are 3 bias settings and why I couldn't set the third?

73 de sv2us

"update"
Yes, Al, the power output was zero and now it is in the region of 5 to 10 Watts.

[chartofmaryland]

Sounds like 1 or both of the LDMOS finals are gone. 5-10 is the driver output +/- the loss through the dead stages. Your needing 2 MRF1550 fet's.

CoM