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| E4407B Tracking Generator Repair |
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| smgvbest:
--- Quote from: analogRF on September 29, 2020, 10:39:02 am ---change the level setting from -10dBm to 3dBm, 1dBm at a time and at each step monitor these signals (all DC) : the ALC monitor that goes from TG to A2A1. The PWR LVL that comes from A2A1. and V1,V2 on HMC346 --- End quote --- I'm at a conference so been a little slow getting things right now, will get them soon as possible Ok, got them (see attachment) Notes: all reading done at 50Mhz, Zero Span. Did one column at a time thru -10 to 3dBm Also read the P15BITG, N15BITG and P5BITG, the supply rails RED Cells is when it went UNLEVEL, but by time i got to ALC_MON/PWR_LVL the UNLEVEL state moved down to -1dB BLUE Cells have variability to them, not a fixed value |
| analogRF:
these numbers look pretty consistent with each other (except one thing that I will mention below) and i cannot see which part might be the main culprit. which part is failing that causes the ALC loop go into saturation. maybe someone else can draw a better conclusion however here is my take and my recommendation 1-the PW_LVL signal coming from a DAC on A2A1 was supposed to be between 0 and -11V (says on the schematic) here it does not go below -9.7 it does not necessarily mean anything and it could have been designed that way because for example V1 should not go too much positive but still it's worth to check if that circuit (PWR_LVL) is ok both on A2A1 and also on the TG board because that signal eventually generates V1 (so what is between V1 and PWR_LVL) 2-The only inconsistency that I see in your measurements and that may be the path to the root cause is that all numbers are and must be similar (very close) for -2dBm and -10dBm settings. Because the TG has to generate -2dBm for both cases. However there is ONE voltage which is very different between the two cases and that is the ALC_MON. In fact between -3dBm and -2dBm it suddenly jumps -1V which never occurs anywhere else. At -10dBm where TG must be generating -2dBm the ALC_MON correctly stands at about -0.17. What happens to ALC_MON at -2dBm and above looks like the TG OFF state. Since I believe the ALC_MON is coming directly from the IGG5 hybrid (please confirm whether this is right or not) the issue may be the IGG5. Or maybe a supply voltage to IGG5 if it has one? 3-Your 5V rails looks a bit low. Is it clean? did you check it when the failure occurred? 4-since the failure moves to lower amplitude as time passes, it is probably affected by heat. Why dont you spray some freeze spray (aim very locally) at different components and see if the error goes away. starting with that IGG5! |
| smgvbest:
--- Quote from: analogRF on October 01, 2020, 02:22:25 am ---these numbers look pretty consistent with each other (except one thing that I will mention below) and i cannot see which part might be the main culprit. which part is failing that causes the ALC loop go into saturation. maybe someone else can draw a better conclusion however here is my take and my recommendation 1-the PW_LVL signal coming from a DAC on A2A1 was supposed to be between 0 and -11V (says on the schematic) here it does not go below -9.7 it does not necessarily mean anything and it could have been designed that way because for example V1 should not go too much positive but still it's worth to check if that circuit (PWR_LVL) is ok both on A2A1 and also on the TG board because that signal eventually generates V1 (so what is between V1 and PWR_LVL) 2-The only inconsistency that I see in your measurements and that may be the path to the root cause is that all numbers are and must be similar (very close) for -2dBm and -10dBm settings. Because the TG has to generate -2dBm for both cases. However there is ONE voltage which is very different between the two cases and that is the ALC_MON. In fact between -3dBm and -2dBm it suddenly jumps -1V which never occurs anywhere else. At -10dBm where TG must be generating -2dBm the ALC_MON correctly stands at about -0.17. What happens to ALC_MON at -2dBm and above looks like the TG OFF state. Since I believe the ALC_MON is coming directly from the IGG5 hybrid (please confirm whether this is right or not) the issue may be the IGG5. Or maybe a supply voltage to IGG5 if it has one? 3-Your 5V rails looks a bit low. Is it clean? did you check it when the failure occurred? 4-since the failure moves to lower amplitude as time passes, it is probably affected by heat. Why dont you spray some freeze spray (aim very locally) at different components and see if the error goes away. starting with that IGG5! --- End quote --- I will check these item out on the IGG5, I did check and I see no bias/dc at it's input so if it's providing the level information I'm not seeing it. I do have freeze spray and will target different IC's starting with the IGG5. I'll also check the P15/N15/P5 without the TG attached so see if it's still being pulled down. |
| analogRF:
basically IGG5 should not need any DC bias, it has a peak detector and should generate a DC proportional to the power level and that voltage after some amplification and conditioning by opamps or transistors will become ALC_MON w.r.t. supplies, I think only the 5V rail seems a little low. check for any ripple/noise specially when the error happens and also for current draw. |
| smgvbest:
--- Quote from: analogRF on October 01, 2020, 03:26:15 am ---basically IGG5 should not need any DC bias, it has a peak detector and should generate a DC proportional to the power level and that voltage after some amplification and conditioning by opamps or transistors will become ALC_MON w.r.t. supplies, I think only the 5V rail seems a little low. check for any ripple/noise specially when the error happens and also for current draw. --- End quote --- when I say no DC/BIAS I mean there is no DC of any kind at the input to IGG5. |
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