- Customer Issue - 2 Updates
- RCA main board - 2 Updates
- clamping circuit help - 3 Updates
| Phil Allison <pallison49@gmail.com>: Mar 15 05:43PM -0700 Hi, if you do repairs for a living, you will sometimes have issues with particular customers. One scenario is when you are NOT dealing with the owner - but some middle man instead. Bad enough. A worse one is when you do not know who the real owner is, cos someone who borrowed (and broke) the item brings it to you *pretending* to be the owner. If they do not return to pick up and pay, anyone can then claim to be the owner and try to obtain the item for the repair cost. So the first question you need to ask any new customer is: " How long have you owned it ? " And if their answer is non very convincing : " Where did you you get it ? " One does not what tot be stuck with items that never get picked up or are maybe stolen or where a dispute about ownership arises. Happens. ....... Phil |
| Rheilly Phoull <rheilly@bigslong.com>: Mar 16 01:31PM +0800 On 16/03/2021 8:43 am, Phil Allison wrote: > ....... Phil Yup, working with the public is bad enough but include the muso's and it's worse. |
| three_jeeps <jjhudak@gmail.com>: Mar 15 11:13AM -0700 > > > Did you confirm the power supply is OK? Getting standby 5V is not enough. You can jump the stby pin to the ps on pin and see if the 12V comes up. If it doesn't, the power supply is bad. If it does, it's the main. > > I'm reading a short across both sides of the fuse 3a/125v to ground, on the tcon board, there's short somewhere.??? > With the LVDS cable disconnected, you should not be getting any low resistance to the ground screws of the TCON. If so, there's a short. The most common reason for a dead short on a TCON are one of the multi layer chip capacitors (they're surface mounted and have no markings). While any dead short is easy to find with an ohm meter, these caps are usually found in groups of two to ten or more all paralleled, so one shorted cap makes them all look bad. Other than a Huntron, the easiest way to find this is to feed a limited current (2 amps tops) into the short with a variable supply and spray the board with freeze spray until the board frosts over. The first cap to thaw is the shorted one. Extremely clever, and useful. Will have to file this trick away. I usually do hunting by keeping the board powered up for a bit then spray targeted components. Thanks J |
| "ohg...@gmail.com" <ohger1s@gmail.com>: Mar 15 04:06PM -0700 On Monday, March 15, 2021 at 2:13:19 PM UTC-4, three_jeeps wrote: > I usually do hunting by keeping the board powered up for a bit then spray targeted components. > Thanks > J That works if the supply maintains the struggle of feeding the short, but most of these more recent circuits (like these TCONs) are fed by buck converters who shutdown when the programmed current value is reached, so the offending load part never gets hot. When using the forced current trick, one must remember to limit the voltage, as sometimes the shorted part may suddenly open under the strain and an over-voltage will then damage something else. |
| "Peter W." <peterwieck33@gmail.com>: Mar 15 10:19AM -0700 On Monday, March 15, 2021 at 12:38:27 PM UTC-4, Hem Jung wrote: > to limit voltage to 25 VDC if my power supply is prone to spikes and I > suspect it is. Can someone suggest a suitable circuit with component > values needed? Thank you. 24V Zener diode to system ground? The shipping will cost more than the device! I am not sure if you mean an actual 'clamping circuit' as much as a voltage limiter. There is no AC that you are trying to limit, just the DC input maximum voltage. Peter Wieck Melrose Park, PA |
| Hem Jung <hemjA@netco.net>: Mar 15 01:36PM -0400 On 3/15/21 1:19 PM, Peter W. wrote: > 24V Zener diode to system ground? The shipping will cost more than the device! I am not sure if you mean an actual 'clamping circuit' as much as a voltage limiter. There is no AC that you are trying to limit, just the DC input maximum voltage. > Peter Wieck > Melrose Park, PA Well, it's a cheap, Chinese 24 VDC switching supply so just trying to avoid spiking at start-up. Is it as simple as a 24 V zener across the input (+ to -)? If so, I have a few of those here. |
| "Peter W." <peterwieck33@gmail.com>: Mar 15 10:58AM -0700 > Well, it's a cheap, Chinese 24 VDC switching supply so just trying to > avoid spiking at start-up. Is it as simple as a 24 V zener across the > input (+ to -)? If so, I have a few of those here. Just that simple, yes. Not sure how much current goes into this device, but you want the diode to be rated at least 2x that current so it does not fail under load. Peter Wieck Melrose Park, PA |
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