Sparkplug
Super Member
I wouldn’t, not suitable. MJE15032/MJE15033 are much better suited, almost an exact match.
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CR620 No Audio...now in protection
- Thread starter gillygilbert
- Start date
gillygilbert
New Member
Thanks to all your help the amp now comes out of protection after following the above noted plan and on the dbt. I do get undistorted sound, though a problem still remains. When testing the idle voltage is when things go sideways. Test point 1&2 have a negative voltage of -18 mV, whereas TP 3&4 is on spec at around +8mV. I have checked the resistance on the trimmer pots and the two pots offer about the same resistance. I'm at a loss at where to start checking to see why the left channel is so out of whack. Can someone please point me in the right direction?
Sparkplug
Super Member
Are you saying that you can not set the right voltage using the trimmer? Also, you’ve replaced 50W transistors with 180W ones and while the amp should still work, it’s not a good thing to do. I know the transistors I mentioned before have different casing so can’t use those either.
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gillygilbert
New Member
Yes. With the trimmers on the highest resistance I can get it to -17mV or at its lowest resistance -21mV. Should the whole channel be a negative voltage, or should it be positive like the other channel?
I also forgot to mention that the DBT starts bright, as normal and then dims but doesn't go out completely. I have a 60w bulb in there.
Sparkplug
Super Member
You shouldn’t do this adjustment while on DBT. If there are no shorts anywhere, DBT isn’t necessary anymore.
Are you setting the negative and positive probes correctly? Turn them around and re-measure. On both channels you should measure +8mV ± 2mV. Before you go off DBT, turn the idle current adjustment trimmers fully CCW first (zero current draw) to be safe. Then re-adjust to the correct value after power on and warm up (CW).
I’d use a 80W or a 100W bulb anyway. The bulb doesn’t turn off, it goes dim as the name indicates.
Are you setting the negative and positive probes correctly? Turn them around and re-measure. On both channels you should measure +8mV ± 2mV. Before you go off DBT, turn the idle current adjustment trimmers fully CCW first (zero current draw) to be safe. Then re-adjust to the correct value after power on and warm up (CW).
I’d use a 80W or a 100W bulb anyway. The bulb doesn’t turn off, it goes dim as the name indicates.
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gillygilbert
New Member
I'll look for a higher wattage bulb. Incandescent bulbs are getting tougher to find.
As for the the positive and negative probes, they are placed correctly in the meter. I'm using chassis ground with the black terminal and red on the test points. I tried another meter last night and got a negative number as well. I also tested both on a new 9v battery and both got the same voltage. I'll re-check the voltages this evening after work.
gillygilbert
New Member
Didn't get a ton of time to test things out but did check on a few things. Here's some observations.
- Used the ground header on the board to ground my multimeter.
- I tested TP-1 shortly after it came out of protection. And it started in the positive 5vm but the voltage was declining rapidly and eventually stopped in the negative at approximately -30mv. Voltages didn't seem too stable though.
- After about 5 minutes of the amp being on I tested voltages at the legs of all the Left channel transistors. Voltages often started high then slowly came down to close to where they should be, again voltages didn't seem very stable. Did notice that on some of the transistors the relay would click in and out as I touched some of the legs of the transistors with the meter probe.
- Tested all the voltages at the headers. The two +12v were about +12.5. The minus -12v was 14.3v. All voltages were stable.
- Tested TR802 in the power supply and got the correct voltages on each leg and the voltage seemed stable.
- Tested test points 3&4 and ended up with a negative number. -2.3mv This was testing correctly previously....
- After being powered on for about 15 minutes I rechecked a few voltages and they were closer to spec right away, unlike the first time I tested them
Sparkplug
Super Member
??? Supposed to be -12 and you’re measuring +14.3? Is that correct? If so, check D805.
Please use the speaker post for ground for now.
Are Tr715 and 717 the new transistors?
gillygilbert
New Member
OMG now that's a typo, I guess I shouldn't have waited until almost bed-time to post! Embarrassing considering I even proofread this last post! The correct answer is -14.3. Yes the TR715 and 717 are new transistors.
Sparkplug
Super Member
LOL, happens to everyone. I always post when I’m doing a couple of other things so end up revising multiple times.
As for supply voltages, they’re fine. Are you still on DBT?
Were the ksc1845/ksa992 used in the other channel too?
Sounds like you maybe having a grounding issue. Please check all your solder work and reflow if necessary.
Take the DBR off, let the amp warm up for at least 15 minutes and re-test.
Edit: Monitor supply voltages over time to see if they fluctuate at all. The same goes for cbe voltages on Tr715, 717.
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gillygilbert
New Member
Yes, been off the DBT for a bit now.
Yes, been off the DBT for a bit now.
Yes I've mirrored the other channel with both the KSC2383/KSA1013 and KSD1845/KSA992
I have gone through and looked at the soldering a few times, the previous owner made a bit of a mess of the soldering and killed off some pads and the odd trace. I will absolutely go through it again in case I missed something the other looks. It will also give me a chance to play with my new desoldering gun I recently treated my self with. I know I can just reflow but when I can use my new toy that's even better. It will give me a chance to see what's under (or probably more accurately what not under) a few of the messier solders.
I should be able to get a chance to look at it for a bit this afternoon.
gillygilbert
New Member
I got a chance to look at it yesterday. Fired it up to test the voltages (off dot) and as I was observing voltages and it started to smoke from what looked like underneath the board. I quickly turned it off and unplugged. What looks like a power rail looks like it got hot. The scorch mark is between J718 and J723. 
After letting it cool off I put it back on the DBT and it now it stays bright. This receiver has definitely been a good learning experience!!
Edit to add: I had a bit of time before I had to leave and I had a suspicion that the problem was being caused by the driver transistors on the that channel so I pulled them (TR723&725) and fired it up on the DBT. Bright, then dim! Diode tested them and they were fine, so I put them back in and DBT stayed bright. Took one out after powering down and it was dim after reinstall. So the DBT is back to normal but now it doesn't come out of protection.
After letting it cool off I put it back on the DBT and it now it stays bright. This receiver has definitely been a good learning experience!!
Edit to add: I had a bit of time before I had to leave and I had a suspicion that the problem was being caused by the driver transistors on the that channel so I pulled them (TR723&725) and fired it up on the DBT. Bright, then dim! Diode tested them and they were fine, so I put them back in and DBT stayed bright. Took one out after powering down and it was dim after reinstall. So the DBT is back to normal but now it doesn't come out of protection.
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Sparkplug
Super Member
Good work.
Are Tr723, 725 new? If so, please check the pin out (ecb, etc.) to make sure they’re installed correctly. Also, please check the emitter resistors on those transistors for shorts, or poor solder connection. Can you post a hi-res photo of the solder side of the board? Something that can be zoomed in?
What does the dc offset voltages look like? Maybe you’re in protection because they’re too high?
Are Tr723, 725 new? If so, please check the pin out (ecb, etc.) to make sure they’re installed correctly. Also, please check the emitter resistors on those transistors for shorts, or poor solder connection. Can you post a hi-res photo of the solder side of the board? Something that can be zoomed in?
What does the dc offset voltages look like? Maybe you’re in protection because they’re too high?
Sparkplug
Super Member
SMs aren’t always updated or correct, there are lots of errors lurking around in them. If a component looks original, go with that as opposed to the SM. In this case here, check with the other channel as well to see if something is original or not.
Check the supply rail voltages going to the main boards to make sure they’re correct and stable (±39V and +30V).
Earlier in the thread, you mentioned there were damaged solder pads, etc., need to repair those properly. I’d use 0.2mm copper tape for pads and traces or AWG #16 to replace traces. You could possibly get away with 0.1mm copper tape but need to pay attention to the current load through the trace. For output and higher current traces use 0.2mm or the AWG #16 wire.
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gillygilbert
New Member
Having a closer look at the solder side I noticed some additional dodgy looking solders hidden by the chassis on the side the output transistors are located. I decided I was going to remove the board and to get a better look and my butter fingers "may" have accidentally dropped the power supply on the board. Yeesh. It wasn't proudest moment that's for sure. Looks like there's a bit of a crack in the board (about 40mm in length) but thankfully no traces were harmed in the making of this disaster. It looks like the main casualty was the trimmer pot for the questionable channel. I guess another Mouser order will be in order. Will hold off until I get the board off and photographed and the resistors checked before I put another order in. Is a Bourns 3386F-1-502LF a good replacement?
I didn't get a chance to check these before I made things more difficult on myself, but took a quick look after and it was 33mv with the smashed trip pot and 6mv on the other channel.
I did compare what was in there as well but everything I replaced were Chonax branded which I think is an Ali Express capacitor that the previous owner installed. I ran them through the capacitor checker and the multimeter and there were quite a few out of spec beyond 20% so replaced the whole works with mostly Nichicon caps. The 1uf caps were all replaced with Wima film caps. The main filter caps were not replaced and are original. I have replacement caps to swap out after the other issues are solved.
Before the self-imposed disaster I did check the outputs from the power supply itself. I wasn't able to find if these values in the service manual to see if they are expected or not.
Red header closest to rear of the amp: 19 mv
Red header closest to front: 24mv and increasing
Blue: 20.6 v
Orange back 20.7v
Orange front. 20.7v
Thanks. I will order some supplies and fix these.
Sparkplug
Super Member
Oh dear … these things happen, hopefully you didn’t get micro cracks in any of the traces. If it’s a 5k trimmer you’re looking for, PV36Y502C01B00 is better but please check the footprint dimensions to make sure it fits on your board. This is a 25 turn trimmer which allows for precise adjustments. Data sheet is available at Mouser.
I don’t have a CR-620 in front of me but below is where the aforementioned voltages plus the ±12V lines are. These need to be solid before anything else works or can be tested.
gillygilbert
New Member
This is the picture of the board's solder side. Hopefully the board doesn't compress it too much. I didn't get to check the above voltages, but will hopefully have time tomorrow to do that. I corrected a couple dodgy solders along the top edge, those were behind the chassis.
Hard to tell anything as it still needs to be cleaned with Denatured alcohol and a brush.
Athanasios
Sparkplug
Super Member
That’s the most important thing right now. All these supply voltages must be rock solid before proceeding.
When mounting the board, make sure you totally clean the copper around the mounting holes to make solid contact.
You’re going to need magnifying glasses to trace that crack to see how far it goes. You may want to use epoxy to repair it so it won’t run any further over time. Don’t epoxy over any traces.
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