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mdc
Joined: 30 Apr 2013
Posts: 50
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| Posted: Tue May 07, 2013 10:20 pm Post subject: |
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On the upside, I think I know what's causing it; the pads on the 7815 have lifted and I think it's causing a short somehow; going to attempt a re-soldering which covers the lifts which should help.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Tue May 07, 2013 10:22 pm Post subject: |
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| mdc wrote: | Aaaaand both those resistors just went poof again.
Now I definitely need to order some more components lol. |
Was the pre amp board installed again? Were they the correct wattage?
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mdc
Joined: 30 Apr 2013
Posts: 50
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| Posted: Tue May 07, 2013 10:32 pm Post subject: |
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| macgyver655 wrote: | | mdc wrote: | Aaaaand both those resistors just went poof again.
Now I definitely need to order some more components lol. |
Was the pre amp board installed again? Were they the correct wattage? |
Nope, left the preamp board out due to the missing components on it.
I just checked the pads and to say they were "lifted" is a bit of an understatement... looks like they've practically disintegrated, and one was DEFINITELY shorting. Will remove all 3 pads and then expose the traces next to them and re-solder 
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Tue May 07, 2013 10:51 pm Post subject: |
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What pads?
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mdc
Joined: 30 Apr 2013
Posts: 50
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| Posted: Tue May 07, 2013 11:20 pm Post subject: |
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All 3 on 7815 lol 
Fixed now. I removed the broken pads entirely, stripped the laquer off the traces and soldered directly to them. Should help eliminate that problem Now just need some replacement .22 1Ws (why the hell are they so rare? They don't even sell them on RS - eBay only by the looks of it) and I'll be back in business.
The fact that the last time I had the unit powered up it actually STAYED ON is quite reassuring, since previously it was going into protect mode without the preamp board attached.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Wed May 08, 2013 12:08 am Post subject: |
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| mdc wrote: | All 3 on 7815 lol
Fixed now. I removed the broken pads entirely, stripped the laquer off the traces and soldered directly to them. Should help eliminate that problem Now just need some replacement .22 1Ws (why the hell are they so rare? They don't even sell them on RS - eBay only by the looks of it) and I'll be back in business.
The fact that the last time I had the unit powered up it actually STAYED ON is quite reassuring, since previously it was going into protect mode without the preamp board attached. |
Mouser has lots: http://www.mouser.com/ProductDetail/Panasonic-Electronic-Components/ERX-1SJR22V/?qs=sGAEpiMZZMu61qfTUdNhGzSYH3SKradLImFTOCG0Fa8%3d
I'm just curious to see if you still have DC on those speaker outputs.
Since your ordering parts did you want to also order the parts required in the service bulletin?
Don't forget to order those diodes also.
How were those transistors on the preamp board I told you to remove and test?
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mdc
Joined: 30 Apr 2013
Posts: 50
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| Posted: Wed May 08, 2013 12:33 am Post subject: |
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Well I was still reading 53V from the speaker ground (black) and the emitter, with the unit fully powered up before the resistors blew again.
What was added/changed in the service bulletin, if you don't mind me asking?
Transistors on the preamp all checked out okay, just need to replace a cap re-fit one of the transistors and I'm sorted on that front
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Wed May 08, 2013 12:52 am Post subject: |
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| mdc wrote: |
Well I was still reading 53V from the speaker ground (black) and the emitter, with the unit fully powered up before the resistors blew again.
What was added/changed in the service bulletin, if you don't mind me asking?
Transistors on the preamp all checked out okay, just need to replace a cap re-fit one of the transistors and I'm sorted on that front |
Was the 53v on all channels or just the SL? Also, take your measurements at the inductors, L101's please.
The bulletin calls to change out all Q103's to 2SC3964 and all R101's to 680ohm. There were thermal problems causing amp failure, which could of been what caused your original failure. If you also notice in the updated schematic I posted they later added another resistor, R102, 330ohm, across VR101. The bulletin does not mention this but you may also want to add that later. But you have to get it working first.
I'd be lying if I said I was not still concerned as to just what took out C502SL and R504SL. Something still smells funny. I would maybe at least check the values of R505sl, R507sl and R508sl, just to be sure. Lets add R509sl also.
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mdc
Joined: 30 Apr 2013
Posts: 50
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| Posted: Wed May 08, 2013 1:06 am Post subject: |
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ALL channels; I was testing primarily off the left hand Darlington for FL, but all channels and Darlingtons came back the same; -53V if I remember correctly for the right-hand ones.
Sounds like a plan; will order the parts tomorrow and pop into town to grab a gas refill for my iron. Fingers crossed once I get everything replaced and plug the preamp board in everything works Is it necessary to replace those missing diode and zener before any more testing?
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Wed May 08, 2013 1:17 am Post subject: |
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| mdc wrote: | ALL channels; I was testing primarily off the left hand Darlington for FL, but all channels and Darlingtons came back the same; -53V if I remember correctly for the right-hand ones.
Sounds like a plan; will order the parts tomorrow and pop into town to grab a gas refill for my iron. Fingers crossed once I get everything replaced and plug the preamp board in everything works Is it necessary to replace those missing diode and zener before any more testing? |
This is why I need you to be testing at the inductors. Now I'm hearing 53v on some and -53 on others. I know what the input voltages are suppose to be. I need to know what is on the output lines just before they enter the relays. If the relays are latching closed after power up then you can measure right at the speaker terminals. But you have to make sure the relays are closed. This is why i want you checking at the inductors.
If your not going to replace those 2 blown diodes then you will have to remove the other 2 complimentary diodes for that channel. The circuit needs to maintain balance.
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mdc
Joined: 30 Apr 2013
Posts: 50
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| Posted: Thu May 09, 2013 7:04 pm Post subject: |
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The main board itself is now stable without the preamp board plugged in. I tested at those inductors as requested. From a black speaker contact to the inductors, it's 53V across the board. From red to the inductors its a few millivolts, although that could be meter drift.
With the preamp board attached, the unit goes into protect mode, and one of the components (most likely C502SL or R504SL) started smoking.
EDIT: Mesasuring for voltage across the speaker contacts yields 0, so I'm guessing the relays aren't latching like you said. I'd imagine that was normal behaviour without the preamp board attached?
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mdc
Joined: 30 Apr 2013
Posts: 50
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| Posted: Thu May 09, 2013 7:19 pm Post subject: |
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Scratch that, those two resistors (R141 and R142) are still blowing.
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mdc
Joined: 30 Apr 2013
Posts: 50
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| Posted: Thu May 09, 2013 9:14 pm Post subject: |
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One additional thing I just discovered is that C141 is reading close to 0 ohms and almost 0 on diode test; the others are all reading a solid infinity/1. Guessing that cap is fried too?
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Fri May 10, 2013 4:10 pm Post subject: |
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| mdc wrote: | | One additional thing I just discovered is that C141 is reading close to 0 ohms and almost 0 on diode test; the others are all reading a solid infinity/1. Guessing that cap is fried too? |
If your testing c141 out of circuit and it's testing shorted then it's no good. In circuit with good R142 and R141 it will test shorted normally.
What's concerning me is the 53v on the output line on all channels. Usually when you have a specific voltage on all channels it's because the opposite voltage is missing, in this case the - voltage would be missing. But you verified the B- was active on a previous test. So we have to look into this further. I would also recommend you leave the preamp board out until this is resolved because it may be feeding back voltage from the main amp board causing that issue.
Funny the protect circuit is not kicking in however it looks like that circuit is powered by the 15v line you are having problem,s with. So you need to get that 15v source circuit resolved to go forward.
While your in there poking around I would check D132, D137 and ZD136.
Did you remove those other 2 diodes on the underside of the board?
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mdc
Joined: 30 Apr 2013
Posts: 50
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| Posted: Fri May 10, 2013 8:22 pm Post subject: |
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| macgyver655 wrote: | | mdc wrote: | | One additional thing I just discovered is that C141 is reading close to 0 ohms and almost 0 on diode test; the others are all reading a solid infinity/1. Guessing that cap is fried too? |
If your testing c141 out of circuit and it's testing shorted then it's no good. In circuit with good R142 and R141 it will test shorted normally. |
I'm testing it in circuit but without R141/R142 present, so I'm guessing it shouldn't be shorted in that case?
| macgyver655 wrote: | | What's concerning me is the 53v on the output line on all channels. Usually when you have a specific voltage on all channels it's because the opposite voltage is missing, in this case the - voltage would be missing. But you verified the B- was active on a previous test. So we have to look into this further. I would also recommend you leave the preamp board out until this is resolved because it may be feeding back voltage from the main amp board causing that issue. |
You and me both :-\ Just out of interest, what's generating that 53V in the first place? The voltage regulators are providing a PD of 30 between them, so I'm guessing it's coming from a separate winding on the main transformer? If so, is it possible one of the rectifiers or filter caps has failed?
| macgyver655 wrote: | Funny the protect circuit is not kicking in however it looks like that circuit is powered by the 15v line you are having problem,s with. So you need to get that 15v source circuit resolved to go forward.
While your in there poking around I would check D132, D137 and ZD136.
Did you remove those other 2 diodes on the underside of the board? |
Haven't removed those two diodes yet but I will if you think it'll help.
At the moment, I'm just worried about replacing R141 and R142 again in case they blow immediately again :-\
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Sat May 11, 2013 12:52 am Post subject: |
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| mdc wrote: |
Haven't removed those two diodes yet but I will if you think it'll help.
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No offense, but I can't help you if you can't follow along properly.
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mdc
Joined: 30 Apr 2013
Posts: 50
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| Posted: Sat May 11, 2013 2:39 am Post subject: |
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| macgyver655 wrote: | | mdc wrote: |
Haven't removed those two diodes yet but I will if you think it'll help.
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No offense, but I can't help you if you can't follow along properly. |
As I said, I'm perfectly happy to do exactly what you say Removing those two diodes was next on my list when those resistors started blowing; just been sidetracked by them since then.
The good news is, D132, D137 and ZD136 all check out okay
"Bad" news is that D144 and D142 test as shorted in both directions. I say "bad" in quotes because at least we know that now; reckon that's why R141 and R142 kept blowing?
Also reading a bit funny is D126 (linked to RLY106), which reads 300 both ways on diode test.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Sat May 11, 2013 3:25 pm Post subject: |
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| mdc wrote: |
As I said, I'm perfectly happy to do exactly what you say Removing those two diodes was next on my list when those resistors started blowing; just been sidetracked by them since then.
They should have been removed before you even replaced any parts and tried running it again. These could possibly be why your preamp board is blowing parts.
The good news is, D132, D137 and ZD136 all check out okay
"Bad" news is that D144 and D142 test as shorted in both directions. I say "bad" in quotes because at least we know that now; reckon that's why R141 and R142 kept blowing?
Then C141 is probably ok as these diodes would show the short across the cap also.
Also reading a bit funny is D126 (linked to RLY106), which reads 300 both ways on diode test.
Remember, when testing a suppressing diode in this type circuit, you must lift at least 1 leg to properly test.
Let me know when you have the 15v source circuit straightened out an we can continue.
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mdc
Joined: 30 Apr 2013
Posts: 50
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| Posted: Mon May 13, 2013 10:58 pm Post subject: |
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| macgyver655 wrote: | | mdc wrote: |
As I said, I'm perfectly happy to do exactly what you say Removing those two diodes was next on my list when those resistors started blowing; just been sidetracked by them since then.
They should have been removed before you even replaced any parts and tried running it again. These could possibly be why your preamp board is blowing parts.
The good news is, D132, D137 and ZD136 all check out okay
"Bad" news is that D144 and D142 test as shorted in both directions. I say "bad" in quotes because at least we know that now; reckon that's why R141 and R142 kept blowing?
Then C141 is probably ok as these diodes would show the short across the cap also.
Also reading a bit funny is D126 (linked to RLY106), which reads 300 both ways on diode test.
Remember, when testing a suppressing diode in this type circuit, you must lift at least 1 leg to properly test.
Let me know when you have the 15v source circuit straightened out an we can continue.
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Thanks
Need to pick up some gas for my iron; been mad with work over the weekend and unfortunately the shops downstairs don't sell it so it means a trip into town.
In the meantime, I was mulling over that theory about the missing -54V line and did a quick test while I'm waiting for gas/parts. I'm reading 108V when measuring between R131 and R132, which appear to be the -54/+54 source rails for the driving section.
I'm getting -54V across C136, and +54V across C137 as well, which is reassuring. AND, the main -B and +B lines are still present at CP505.
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