Home |
Search |
Today's Posts |
|
Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
Reply |
|
LinkBack | Thread Tools | Display Modes |
#1
Posted to sci.electronics.repair
|
|||
|
|||
HP 5385A freq counter repair
On 9/24/2016 11:18 PM, Phil Allison wrote:
... If the 5V rail goes out of tolerance, an SCR is triggered to ... ... the 5V rail would be full of HF switching noise which could trigger the SCR. ... How would the monitoring circuit work, in general terms? |
#2
Posted to sci.electronics.repair
|
|||
|
|||
HP 5385A freq counter repair
Bob Engelhardt wrote:
-------------------------- ... If the 5V rail goes out of tolerance, an SCR is triggered to ... ... the 5V rail would be full of HF switching noise which could trigger the SCR. ... How would the monitoring circuit work, in general terms? ** Essentially, just a 400mW Zener diode rated at 4.7 or 5.6 volts. The SCR has a resistor of say 100ohms from gate to ground and the Zener connects from that to the 5V rail. Takes about 0.8V to trigger the SCR so about 8mA of Zener current. I have added such to several linear & SMPSs to protect digital boards from faulty PSUs. In one case, I had to replace about 100 digital ICs after a linear 5V supply failed to circa 10V DC. Luckily they were all in sockets. ..... Phil |
#3
Posted to sci.electronics.repair
|
|||
|
|||
HP 5385A freq counter repair
On 8/22/2017 2:32 AM, Phil Allison wrote:
Bob Engelhardt wrote: -------------------------- ... If the 5V rail goes out of tolerance, an SCR is triggered to ... ... the 5V rail would be full of HF switching noise which could trigger the SCR. ... How would the monitoring circuit work, in general terms? ** Essentially, just a 400mW Zener diode rated at 4.7 or 5.6 volts. The SCR has a resistor of say 100ohms from gate to ground and the Zener connects from that to the 5V rail. Takes about 0.8V to trigger the SCR so about 8mA of Zener current. I have added such to several linear & SMPSs to protect digital boards from faulty PSUs. In one case, I had to replace about 100 digital ICs after a linear 5V supply failed to circa 10V DC. Luckily they were all in sockets. .... Phil OK ... I was thinking that the AC switching noise itself would have to be detected, but it sounds like you just need to look for the noise peaks, which would exceed the zener htresho0ld. Bob |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
What's your opinion of this "Radio Shack" Freq. Counter | Electronics Repair | |||
Ramsey CT-90 Freq counter | Electronics Repair | |||
does the freq. counter contribute anything in computer motherboard repair services? | Electronics Repair | |||
B&K 1822 Freq Counter Manual Copy Wanted | Electronics Repair |