| Electronics > Repair |
| Fluke PM6666 counter freezing after 3 seconds from turning on. |
| << < (20/27) > >> |
| thinkfat:
Well yeah, that doesn't look OK. The signal is out of spec already without the GPIB card, with the additional load of the card it's not improving of course. I suspect that there's something wrong with the output drive of IC104, it just cannot source enough current to drive the line high fast enough. The counter itself seems to be happy, though. The fall time of the signal seems to be OK'ish. If you want to try a small experiment, get a resistor of maybe 500 Ohms, connect it between the clock signal and +5V, see if this improves the situation. If you see a difference, try a smaller resistor, maybe down to 200 Ohms. However, lifting the clock output pin of IC104 and feeding it into a Schmitt trigger buffer and from there back into the board would be a better idea. Maybe, just maybe, touch up the solder joints of IC104. If you have a cold joint, that could explain it, too. |
| shakalnokturn:
Agreed, that doesn't look fantastic. What does that 5MHz look like on the PM6669 with GPIB installed? |
| pizzigri:
Well, IC 105 and 106 are mounted on a socket so maybe I could lift them out and clean the contacts, ow that I think about it it was a standard protocol for any problems on Macs with the ram. Will try that. And OK for the resistor, that’s next. I don’t have the 6669 any more- waiting on an Hp 5385a with which I replaced it. |
| pizzigri:
Wow what a difference, here’s the result of a R500 between +5v and clut on the signal: ...however it still locks up after 3 secs. I'll try now a R300 |
| pizzigri:
so taking +5v from pin 22 of IC104, closer than the 5v pin on the oscillator connector... going with a R280 tht's what I have now. However, the meter doesnt boot, if I feed it this way |
| Navigation |
| Message Index |
| Next page |
| Previous page |