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?
CDM750 TX pwr problem
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CDM750 TX pwr problem
There are 10 kind of people: Those who understand binary and those who don't.
Re: CDM750 TX pwr problem
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
another thread if this is in fact the case.
Jim
Paul wrote: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
- Posts: 1515
- Joined: Tue Jun 10, 2003 8:52 am
Re: CDM750 TX pwr problem
Maybe try reading another radio's tuning data and writing that into it.
Re: CDM750 TX pwr problem
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.
Re: CDM750 TX pwr problem
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.
(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.
There are 10 kind of people: Those who understand binary and those who don't.
- chartofmaryland
- Batboard $upporter
- Posts: 411
- Joined: Sat Dec 28, 2002 11:25 pm
- What radios do you own?: Alot
Re: CDM750 TX pwr problem
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
CoM
If the lights are out when you leave the station and then come on the second you key up, you know you have enough power.