ICOM IC-7600 : NO TX power - repairing, part 1
I lost TX power on Icom IC-7600 before ARRL SSX DX contest. Tube PA failured and than Icom did not have any TX power. Just Id bias current was shown on the LCD.
At first I looked at pre-driver, driver and PA voltages, all OK. Than I took R&S FSL-6 with small capacitor probe and measure RF power. There was only abt -60 dBm at the input of PA board. Than I connected generator on 14,1 MHz with 0 dBm and great, there is abot 70W at the output. PA board is alive! Than I looked at schematic again. There is small MMIC amp called BGA 616 with 18 dB of gain and some switching PIN diodes. I am affraid, this parts are under two another boards: Preamp board and Filter board. It was not easy to take it out, but I used CuAg wire and cleaned pins from the tin.
Than I measured RF power at PIN diode D604. Set TRX to 14,1 MHz, mode RTTY and press TX. There was about -13 dBm. On D601 was quite the same, so diode switching is right. Continued to D201 which is TX way switch diode, still the same. So all is clear. MMIC amp is dead. Instead of abt + 3 dBm at the MMIC output, there is -60 dBm.. not so bad for ATT, but for amp? :)
At first I looked at pre-driver, driver and PA voltages, all OK. Than I took R&S FSL-6 with small capacitor probe and measure RF power. There was only abt -60 dBm at the input of PA board. Than I connected generator on 14,1 MHz with 0 dBm and great, there is abot 70W at the output. PA board is alive! Than I looked at schematic again. There is small MMIC amp called BGA 616 with 18 dB of gain and some switching PIN diodes. I am affraid, this parts are under two another boards: Preamp board and Filter board. It was not easy to take it out, but I used CuAg wire and cleaned pins from the tin.
Than I measured RF power at PIN diode D604. Set TRX to 14,1 MHz, mode RTTY and press TX. There was about -13 dBm. On D601 was quite the same, so diode switching is right. Continued to D201 which is TX way switch diode, still the same. So all is clear. MMIC amp is dead. Instead of abt + 3 dBm at the MMIC output, there is -60 dBm.. not so bad for ATT, but for amp? :)
Preamp and BPF boards
Please disregard my previous, dumb, question, this should have been obvious to me had I used my brain a bit. The 1N4148 diode pair and the series capacitor are basically identical to a dual TVS device.
ReplyDeleteHave you encountered any additional problems with your IC-7600? I have one on my bench that has blown the IC201 BGA616 four times now.
any chance you recorded the DC voltages around that circuit? Replacing the BGA616 did not fix it. -12dbm input/-47 dbm output
ReplyDeleteJan
ReplyDeleteDid you check the DC level at the output of the BGG616 (IC201 Pin 3)? The output is enabled through the T8V line via Q202/Q201. Otherwise, I would look for significant loading on the line, possibly bad caps at C202/C204. ALso, disconnect the feed line to the Control Unit to make sure there is no loading farther downstream.
The BGA616 is a very sensitive MMIC, and although it has internal ESD protection, it could still possibly be damaged during handling and installation. That would be a worst case scenario, but in the end, you may have to consider it.
Good Luck
Dave
KB7JS
I repair radios for the Coast Guard every day. I know the precautions and safety measures. ---- but,,,somehow, I must have wiped out the IC. Luckily, I got more of them. Changed it again and it's working. I've captured the spectrum analyzer screens and DC levels into my pdf service manual in case I ever see this again. I was seeing 3.6V on pin 3. Now it's showing me 4.7V. I'm thinking that IC was bad from the start. Thanks for your help, Dave
ReplyDelete