petehall347
the brandy coffee man
i will have to get the manual and look later .
Onkyo TX-8500 mkII digital tuner indication.
- Thread starter anderslober
- Start date
anderslober
Yikes...not again!
Shucks Pete...disregard the last post about voltages......my voltages are fine...minus is minus and plus is plus.
I am thoroughly conundrummed by this'un! All is new on the display board......the tuner works fine....great stereo an'all...just frozen friggin' digital display.
What else can we measure?
I am thoroughly conundrummed by this'un! All is new on the display board......the tuner works fine....great stereo an'all...just frozen friggin' digital display.
What else can we measure?
anderslober
Yikes...not again!
What does the oscillator do? Does it oscillate a signal to the display somehow? Make the display count up/down as you move the tuning dial?
Frak!......I still hate tuners!
Frak!......I still hate tuners!
petehall347
the brandy coffee man
no idea how it works .
it will be things telling other things what to do . i just suspected the osc. might tell the display driver what to do and its maybe not telling it .
i still have to get the manual .
it will be things telling other things what to do . i just suspected the osc. might tell the display driver what to do and its maybe not telling it .
i still have to get the manual .
petehall347
the brandy coffee man
check voltages at q721 .
anderslober
Yikes...not again!
Voltages on q721 are good. B is 3.9v....C is 7.5v...E is 3.8v. What is a good sub for 2sc461 ? Ksc1845?
What about the 1sv55?.........'double-diode-thingy'.........could it be this? What is a good sub?
What about the 1sv55?.........'double-diode-thingy'.........could it be this? What is a good sub?
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petehall347
the brandy coffee man
2sc 461 ...
30V, 0,1A, 230MHz
30V, 0,1A, 230MHz
My 2 cents - if tuner is tuning in stations correctly, then fiddling with the local oscillator circuits is going to make problems, not cure them. The display circuit takes the local oscillator signal and generates frequency information from it. If there is a problem with the local oscillator, then tuner won't work at all....
Two more (but not likely) thoughts - first is maybe one of the 2 little caps next to the crystal went bad. Also check continuity of cable from local oscillator (including the grounds) and the first prescaler. Good luck with it.
Unfortunately a scope would help to narrow down the problems pretty quickly. If you have access, check for signal going out of prescalers into the large chip, and signal around the large chip.
Two more (but not likely) thoughts - first is maybe one of the 2 little caps next to the crystal went bad. Also check continuity of cable from local oscillator (including the grounds) and the first prescaler. Good luck with it.
Unfortunately a scope would help to narrow down the problems pretty quickly. If you have access, check for signal going out of prescalers into the large chip, and signal around the large chip.
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anderslober
Yikes...not again!
Thanks for the excellent info. I will leave the oscillator alone as the tuner works just fine. The fault must be on the display board. Have we absolutely narrowed it down to this? I will recheck everything on the board.....caps, resistors ...all will be checked. All the IC's are new.
Continuity from tuner board to display board is good. Grounds are good.........
Man, I hope we can fix this.
Could it be the display itself?
Continuity from tuner board to display board is good. Grounds are good.........
Man, I hope we can fix this.
Could it be the display itself?
Thespeakerdude8
Super Member
Did you ever get this issue resolved? Im going through the exact same thing ...replaced the driver chip, replaced Q721 with ksc945..my display is stuck @ 189.3mhz...half of the 1 is lit up.
Bumping this old thread, I'm happy to report that after quite a bit of trouble shooting (thanks in part to the extra available time I have due to the COVID-19 stay at home orders) I was able to fix this issue. The OP stated that his display was stuck on 186.8. However mine, like Thespeakerdude8, was stuck on 189.3 with the bottom half of the '1' missing. So I don't know if these are actually the same problem, but for me, ultimately replacing Q715, the HD74S112P did the trick. I say "ultimately" because getting to that point was a long and winding road. After measuring key voltages at various points upstream of the display board such as TR4 and Q721, I was pretty certain that the problem was somewhere on the display board itself. I even pulled the OSC IN pin just to confirm that doing so had no impact on the frozen display. On another thread, someone suggested replacing the crystal stating that they can go bad with age due to the way they are manufactured. Interestingly I found that the existing crystal was labeled as 7.2 Mhz, but I had ordered a 6.5536Mhz from DigiKey based on the schematic so that's what I used. Replacing the crystal didn't solve the problem so I left it in and went on to continue troubleshooting. I started taking voltage readings on Q715. I noticed the handwritten annotation on the schematic showed 1.7V at Pin #9 of Q715, but I measured only 0.9V. I measured 1.1V on Pin #1 as per the schematic, so I thought that something downstream of Q715 might be pulling down Pin #9. Next I removed Q714 to see if that changed either the display or the voltage on Pin #9 of Q715, but nothing changed on either. So I decided to order all new chips including the frequency counter and display driver Q712, the MSM5525. Ebay is your friend when trying to find obsolete chips, but long delivery times are frustrating. I was able to find an MSM5525RS. I didn't know if the "RS" made a difference and I could not find a datasheet online so I took a chance and ordered it. Three weeks later it arrived. When I replaced the existing MSM5525 with my new MSM5525RS, the display was no longer locked on 189.3! Instead it was stuck on "J -". I wasn't sure if that was progress or not. Next to arrive was my new HD74S112P. When I installed it, the voltage on Pin #9 was now at 1.7V and the display flickered the "J" and the "-" when I turned the tuning dial. That was progress for sure, but obviously there was still more to do. I next changed Q713 and Q714, but the display still showed the "j -".. Frustrated that there was nothing left to change on the display board, I decided to reinstall the original MSM5525. I turned on the power and held my breath and voila!, the display light up with numbers and changed as I turned the dial. So it seems that Q715 was really the culprit after all.
I next thought let me go back and put back the original 7.2Mhz crystal. When I did that, the calibration of the display was thrown way off. So I put back the 6.5536Mhz crystal, and the calibration of the display was spot on. So I'm wondering if someone before me tried swapping the crystal but only had on hand a 7.2Mhz. When that didn't fix the problem, perhaps they just left it in and gave up on further troubleshooting. I don't know the history of my unit since I purchased it on eBay several years ago.
BTW, I was finally able to track down a datasheet for the MSM5525 buried in an old Ambit catalog. Google "Ambit MSM5525" or go to the americanradiohistory.com website.
https://www.americanradiohistory.co...bit-Catalog/Ambit-International-Catalog-2.pdf
I still don't know the difference between the 5525 and the 5525RS other than the RS did not work for me. But perhaps my brand new $30 chip was DOA? I have no way to determine if there is something different about the RS version causing it to behave the way I described, or if it is just defective.
Next problem to fix is no AM. I'm hoping that will be as easy as replacing the HA1151, which is now on order from Ebay. Strangely, all of the voltages on the pins match what is shown on the schematic, but I've read in other threads that even with the correct voltages around the chip, the chip can still be bad. Fingers crossed....
I next thought let me go back and put back the original 7.2Mhz crystal. When I did that, the calibration of the display was thrown way off. So I put back the 6.5536Mhz crystal, and the calibration of the display was spot on. So I'm wondering if someone before me tried swapping the crystal but only had on hand a 7.2Mhz. When that didn't fix the problem, perhaps they just left it in and gave up on further troubleshooting. I don't know the history of my unit since I purchased it on eBay several years ago.
BTW, I was finally able to track down a datasheet for the MSM5525 buried in an old Ambit catalog. Google "Ambit MSM5525" or go to the americanradiohistory.com website.
https://www.americanradiohistory.co...bit-Catalog/Ambit-International-Catalog-2.pdf
I still don't know the difference between the 5525 and the 5525RS other than the RS did not work for me. But perhaps my brand new $30 chip was DOA? I have no way to determine if there is something different about the RS version causing it to behave the way I described, or if it is just defective.
Next problem to fix is no AM. I'm hoping that will be as easy as replacing the HA1151, which is now on order from Ebay. Strangely, all of the voltages on the pins match what is shown on the schematic, but I've read in other threads that even with the correct voltages around the chip, the chip can still be bad. Fingers crossed....
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Well, replacing the HA1151 chip did not fix the no AM problem. All the voltages around the pins still measured correctly as per the schematic. I checked the output on Pin #11 with a signal tracer amp and had silence as I turned the tuning dial back and forth. So it seemed like there was no RF coming into the HA1151 from the tuning cap. C205, the 470pf polystyrene cap became suspect since it is the link between the tuning cap and the RF input on the board. Polystyrene caps are known to fail. I checked it in-circuit with my cap-res-trans meter and it measured 33.1 ohms. As I was removing the clip test leads all of a sudden the reading changed to 47pf. I turned on the power and for the first time i could faintly hear sound as I turned the tuning dial. The signal was so weak that the signal meter didn't even budge. I still had the test leads clipped to the cap and as I was jiggling them free, the reading shot up to 520pf and the sound popped out load and clear! So it appears that there is an internal intermittence with C205. Replacements are on their way from Mouser now! Another mystery solved!
mufc
New Member
Thanks Chixit for all the great info. I saw an TX-8500 just sell on ebay for $1300. Long story short I have one and its stuck on 189.3, so I decide to research again and cam across your update. Going to get a HD74S112P and try it out. AM is working on my receiver, so don't have to deal with that.
Thanks again for the details and all your work.
Thanks again for the details and all your work.
