Chosen Solution
This has several resistors and an area about the size of a quarter that is looking a burnt brown on the pcb near the front of the unit. There are about 5 or 6 ringed resistors total in this area. Tested and results below. When using the tuner/radio portion all seems to be fine (uses the bypass mode for radio). When using the bypass feature (which only utilizes the 2 rear channels I believe) for the video/theater audio, this works too. The option to use anything that utilizes the DSP portion is a intermittent. Just a low hum or his is presenting thru speakers sometimes. Shame to toss this in the trash because this receiver is an oldy but goody. Seems like I could replace a few resistors and all would be well? Hopefully the community here will be familiar with the issue. Thanks in advance! I have located a service manual but lack the knowlege to read it (link below). I also have pics of the overheated resistor location.
Actual board part number (I think) is ncar-5121. These are numbers from the board anyway. I’ve resoldered all of those resistor and transistor contact points plus re-soldered all the contacts on about 1/3 of this board. I was able to get my magnifying headset on and locate a few bad / cracked solder points as well in other areas. Improvement has been noticed as not all of the resistors listed below are as hot as they were with the exception of the 3 listed below. https://www.dropbox.com/s/m66gysdhfqyojz… Svc manual https://www.dropbox.com/s/9sjwtrqncm77du… The resistors and their tested values are: r930 = 118.8 ohm HOT TO TOUCH! r929 = 118.5 ohm HOT TO TOUCH! r928 = 18.4 ohm HOT TO TOUCH! r935 = 22.1 ohm r923 = 1.5 ohm r925 = 11.4 ohm r926 = 11.5 ohm These seem to be within range? Values for outputs for these voltage regulators tested by touching the negative to the G (?) Terminal and pos to the O terminal (is this the correct way to test?): Q921 = + 11.7v q922 = -11.6v q923 = + 6.02v q924 = - 5.8v then drops to 0 usually (this one drops voltage after heating up) q925 = + 5.5v I am currently at a standstill and need help with schematic. I specifically need help with the next troubleshooting step. The service manual is provided and I believe the resistors and regulators in question are on page 36. If components need replaced could you provide suggestions on comparable replacements if needed? Where to get? Thanks. I’ve been studying on how to test these voltage regulators as well. To repeat - I do not know how to read schematics. I wouldn’t have gotten this far without help. It took a bit of hard study to be able to read that schematic and still don’t understand much but am able to limp thru so far :) I look forward to the next step :)
@longoverdue Hi Edward, My experience with old electronics is that capacitors deteriorate with age. Look for bulges on the top and leaking brown goo. I fixed a NAD amplifier and a Technics turntable by doing this. Here is a link for the service manual for your receiver which should help: https://www.hifiengine.com/manual_librar… HiFi Engine is a very good site for old electronics. You may already know this but it may help others reading this.
@longoverdue we would need to know what regulator your Onkyo is using. If it has a thermal shutdown, then yes it will. Most voltage regulators do not have a thermal shutdown so if you get into a thermal runaway which exceed the maximum temperature your voltage regulator will usually go up in a puff of smoke. Going by your data I would replace the regulator and install a heatsink for it. Go with something like a NJM79M06 which looks like it was used on your board anyway and according to your schematics should fit. See what that will give you. Get the data sheet and the part if needed from here
