| Author |
 Topic  |
|
tony
Bronze Member
United Kingdom
142 Posts |
 Posted - 08/13/2008 : 15:30:18
|
Thanks doc, as Laurie said it was D3, which is 5.1v and evidently does look more important than it is!
Well, I don't have an oscilloscope, but with the pedal on, r44 has about .9 of a volt going across it and with the pedal off comes up as 9.86k, so I don't know, it looks fine, as far as I can tell.
Not to jump the gun (done that once already) but do you think it could be a dead electrolytic somewhere? I know this pedal has spent pretty much the past 20-odd years sitting in a centrally heated house. having said that, it was fine when I got it.
Something that might be worth mentioning - a little while before it broke, I had both outputs going into one of those new Digitech Hardwire reverbs. Had everything up to full and the most mad feedback erupted out of nowhere - it nearly blew my head off. - I don't know if this was the famed DD 2 self oscillation or something else? |
Edited by - tony on 08/13/2008 15:36:22 |
 |
|
|
Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/13/2008 : 15:37:16
|
| Can you maybe (carefully!) connect R44 to the input of an amp? One side of R44 is connected to ground, the other to Q9. Connect the "hot' wire of the amp input to the side connected to Q9 and the ground side to ground (or the pedal case). If you do that and can hear the delayed sound (echos) clearly, it will tell us something. |
|
|
|
tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/13/2008 : 16:00:14
|
Done it. Thank God for George l's!
The output is the same weak, barely audible echo signal - exactly like plugging it in normally through the "stereo" output". |
|
|
|
Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 08/13/2008 : 16:24:25
|
Hi tony, Laurie & Guys
Not wanting to be too critical, or sound anal.
But I would place a small cap, like a 0.1uf in series with the hot (inner wire) of the Audio cable that you are probing around on the PCB with.
And then probe around with the free end of the cap.
This will minimize any loading on the DD-2 circuit, & correctly couple the AC signal into your test amp.
As well a minimized popping or worse, from directly coupling DC into the input of your test amp or onto your DD-2.
Regards Dr. Bob |
Edited by - Dr. Bob on 08/13/2008 16:26:39 |
|
|
|
Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/13/2008 : 16:56:05
|
quote:
Originally posted by Dr. Bob
Hi tony, Laurie & Guys
Not wanting to be too critical, or sound anal.
But I would place a small cap, like a 0.1uf in series with the hot (inner wire) of the Audio cable that you are probing around on the PCB with.
And then probe around with the free end of the cap.
This will minimize any loading on the DD-2 circuit, & correctly couple the AC signal into your test amp.
As well a minimized popping or worse, from directly coupling DC into the input of your test amp or onto your DD-2.
Regards Dr. Bob
Good point Dr. Bob! (R44 is safe - but for other prodding, a cap is a good thing)\
I'll have a look at the schematic again tonight when I get home and we can probe some more... |
|
|
|
tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/13/2008 : 18:10:00
|
Dr Bob - I've added a cap to my probe. Thanks!!
Laurie - I've got clear echoes from R44. Earlier, when I was testing the signal from R44, I was (unknowingly) touching the insulated bit of the lead on the component side of the board. I just looped a bit of the cap lead around the solder side contact and I get nice clear echoes - along with a fair bit of interference from the crude cable probe.
One thing worries me - even with the clear echoes, I still only get one/two repeats - even with all the controls at maximum.
EDIT:
Tried this again. Running off of R44, "hold" mode works fine. All the other modes produce a maximum of one, maybe one and a half echoes with the "feedback" control wound all the way up. All delays are totally loud and clear.
By the way, Laurie and Dr Bob, thank you for all your help so far... |
Edited by - tony on 08/13/2008 19:28:24 |
|
|
|
Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/14/2008 : 05:42:01
|
Well now that's interesting...
First off, if things sound clear, then the loss of volume is past this point. Plus the feedback isn't working right.
Interestingly, both these things come together around IC2 and Q8. So...
1) probe both sides of C29 and see if the signal is as clear as on R44.
2) If it is clear in step (1) above, do the same on C28, then "terminal 12" on the board.
3) if the signal isn't clear in step 1 above, probe pin 14 of IC 2 (the NE570)
4) probe pin 10 of IC2. Check pin 13 of IC2 has 9VDC on it.
Let us know what you find... |
|
|
|
tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/14/2008 : 13:05:48
|
Right, my morning's probing has yielded the following results:
1). Echoes not clear on both sides of C29.
2). n/a
3). Very clear echoes on pin 14 of IC2 (NE570)
4). Pin 10 of IC2 (NE570) - echoes not clear. Pin 14 of IC2 has 8.81v on it (I think the battery might be starting to get tired).
|
Edited by - tony on 08/14/2008 13:12:31 |
|
|
|
Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/14/2008 : 15:27:20
|
quote:
Originally posted by tony
Right, my morning's probing has yielded the following results:
1). Echoes not clear on both sides of C29.
2). n/a
3). Very clear echoes on pin 14 of IC2 (NE570)
4). Pin 10 of IC2 (NE570) - echoes not clear. Pin 14 of IC2 has 8.81v on it (I think the battery might be starting to get tired).
Well that seems definitive... the problem is with the NE570. Now, we just need to decide if it is a dead chip or a bad control signal.
1) What is the voltage on pin 16 of the NE570?
2) Do you have any way of testing C21? (or do you have a 100p cap you can replace it with?).
3) What do the solder joints on the NE570 look like?
4) Can you confirm "0 ohms" between pin 4 of the NE570 to the pedal case?
If all those things above are OK, then it has to be the chip (not the first time I've seen this). The good news is that they can be obtained... for a price.
http://www.smallbearelec.com/Detail.bok?no=235
|
|
|
|
tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/14/2008 : 16:25:44
|
1).The voltage reading on pin 16 always starts at between .20v - .40v, then drops rapidly to about .09v
2). Sorry, my multimeter doesn't test for capacitance. The nearest component shop is pretty far and the weather here is appalling. I can get one if need be, though.
3).The solder joints look flawless.
4).No, pin 4 of the NE570 to the pedal case to ground reads 1.5ohms. |
|
|
|
Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/14/2008 : 16:36:03
|
Based on everything so far, if this was my DD-2, my next activity would be to replace the NE570 - that will almost certainly fix it (nothing is for certain until you try though!)
|
|
|
|
tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/14/2008 : 17:04:09
|
There's one on the way! Along with a socket. Found one in the UK so I won't have to wait for international postage.
I can't tell you how much I appreciate all your guidance on this.
What do you make of the 1.5 ohms to ground? Was 0 ohms to ground normal or an indication of failure? Also, from the schematic it looks like pin 16 is sending out the signal - is that right?
Edit: After looking at the data sheet I can see that pin 16 is the external capacitor pinout for rectifier 2 - which makes an incredibly vague kind of sense. |
Edited by - tony on 08/14/2008 17:11:22 |
|
|
|
Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/14/2008 : 17:12:04
|
quote:
Originally posted by tony
There's one on the way! Along with a socket. Found one in the UK so I won't have to wait for international postage.
I can't tell you how much I appreciate all your guidance on this.
What do you make of the 1.5 ohms to ground? Was 0 ohms to ground normal or an indication of failure? Also, from the schematic it looks like pin 16 is sending out the signal - is that right?
1.5 Ohms is as good as "short"... anything less than about 5 Ohms on an analog meter is OK. Pin 4 should be short to the case, so it's all OK.
Pin 16 is a control pin. Signal out is pin 10.
Glad u could get one locally. Keep us posted!
|
|
|
|
Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 08/14/2008 : 17:12:54
|
Hi Tony, Laurie & Guys
If you look at the schematic for the DD-2
you will see that the NE570 gets its 9V rail directly from before the
the LM78L05 regulator (IC10)
If I remember correctly you mentioned that the plug pack you WERE using has a really high voltage output,
over 20 Volts at one point if I recall, or was that a glitch with your multimeter?
The VCC on the NE570 is just a little over 20V.
It makes sense that you guys have tracked it down to the NE570 IC.
I would also me checking any other part that gets it 9V (supposedly regulated rail) which wasn't the case with your pedal.
From that part of the circuit.
This was EXCELLENT Detective work Guys, these sorts of remote diagnostics & repairs can be very difficult to perform.
Not preempting a final outcome,
you guys deserve a couple of elephant stamps & 3 gold stars for all your effort.
Here is a FREE link to the PDF for the NE570:
http://www.datasheet4u.com/html/N/E/5/NE570_ONSemiconductor.pdf.html
Tony, the main page is a great link to bookmark, for future reference:
http://www.datasheet4u.com
Regards Dr. Bob |
|
|
|
Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/14/2008 : 17:20:24
|
Hi Dr. Bob! The PSU reading was the multimeter setting. Not to say that the pedal didn't receive a jolt somehow earlier in it's life.
The clarity of the signal going into the NE570 leads me to believe that everything else in the audio path is OK... We shall see, but I am optimistic.
You are weocme to the help tony! Just buy me a beer next time I'm in the UK   |
Edited by - Laurie on 08/14/2008 17:20:36 |
|
|
|
Topic |
|
DD 2 problems
