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Quad 66 Pre-amp stuck in standby

PostPosted: Sat Jul 30, 2016 9:58 pm
by marc
Hi all,

As per the title I have a Quad 66 pre-amp which is stuck in standby and it doesn't appear to be a fault with the remote control as I have 2 and the pre-amp doesn't respond to either.

Now before I start digging deep into it's bowels I was wondering if anyone out there who may have experience of Quad gear would know what I should be looking for and point me in the right direction.

There is a PDF of the service data available here....http://quad-hifi.info/public/quad+66.+p ... 128%5D.pdf

Cheers,
Marc.
Quad 66 preamp.jpg
A photo pinched off the net to show what it looks like.
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Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sat Jul 30, 2016 10:14 pm
by PYE625
Hi Marc,

Without stating the obvious, you need to be absolutely sure that the remote controls are fully operational first.

In the amp, a common cause of problems are dry joints, in particular on the through-pcb pin connections.
You could then check the PSU rails in the 66 and ensure none are being dragged down (a faulty IC will cause this, and will be hot).
Also, scope to see if any data is coming from the IR receiver eye when activating the remote controls.

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sat Jul 30, 2016 10:23 pm
by marc
PYE625 wrote: Without stating the obvious, you need to be absolutely sure that the remote controls are fully operational first.

Hi Andrew,

Yep the remotes are both working fine (one is actually new) they still control the Quad CD player.
I'll have a look inside the beasty tomorrow and follow your advice.

Cheers
Marc.

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sat Jul 30, 2016 10:30 pm
by PYE625
:aad

A lot of C-MOS in there, so watch the static :qq1 :qq1

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sun Jul 31, 2016 10:16 am
by rob t
The remote circuit can be checked by putting a scope on the control input .
Which is the output from the RC amp (IC4)?
Rob T

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sun Jul 31, 2016 12:18 pm
by marc
rob t wrote:The remote circuit can be checked by putting a scope on the control input .
Which is the output from the RC amp (IC4)?
Rob T

Hi Rob & Andrew.

Rob,
The RC amp is IC400 and it appears to be OK, i'm seeing pulses on pin 11 (control input) when actuating the remote.

Andrew,
All the IC's seem to be running cool, Ill do some voltage checks later.

Marc.

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sun Jul 31, 2016 12:43 pm
by Cathovisor
Before you do anything else, check that you have a clean 5V ± 0.25V on pin 40 of the processor IC302. It'll be a waste of your time if that's not the case. The 5V regulator (L387) is one of those clever ones designed to reset a CPU upon application of power. It'd be worth checking that it's not holding the CPU in reset after checking it has an output.

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sun Jul 31, 2016 2:40 pm
by PYE625
Cathovisor wrote:Before you do anything else, check that you have a clean 5V ± 0.25V on pin 40 of the processor IC302. It'll be a waste of your time if that's not the case. The 5V regulator (L387) is one of those clever ones designed to reset a CPU upon application of power. It'd be worth checking that it's not holding the CPU in reset after checking it has an output.



A good point :qq1

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sun Jul 31, 2016 3:00 pm
by marc
Hi Catho & Andrew,

Pin 40 of IC 302 is 3.66v

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sun Jul 31, 2016 3:36 pm
by PYE625
marc wrote:Hi Catho & Andrew,

Pin 40 of IC 302 is 3.66v


It should be 5v. Check to see if you have 12v going to the 5v regulator (IC303), if so, the regulator is probably faulty, but IC302 could of course be faulty and dragging down the 5v.

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sun Jul 31, 2016 3:53 pm
by marc
PYE625 wrote:
marc wrote:Hi Catho & Andrew,

Pin 40 of IC 302 is 3.66v


It should be 5v. Check to see if you have 12v going to the 5v regulator (IC303), if so, the regulator is probably faulty, but IC302 could of course be faulty and dragging down the 5v.

Hi Andrew,

It looks like only 3.6v is getting to the regulator :aaq
Going back to the transformer I've got 10vac before d306 but only 3.6 vdc after.....have I got a duff rectifier ? Time to take it out and check it me thinks. :aaq

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sun Jul 31, 2016 4:01 pm
by PYE625
Are both the transformer secondary fuses ok?

Be careful if anything is dragging down the 12v.
Check all volts in psu.

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sun Jul 31, 2016 4:17 pm
by Cathovisor
First I'd say pull both fuses and check you have 10V AC on each half of the secondary, then examine the fuses.

Once you've done that, lifting one end of L300 and checking if 12V appears there should tell you if the regulator's the culprit.

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sun Jul 31, 2016 4:38 pm
by marc
PYE625 wrote:Are both the transformer secondary fuses ok?

Be careful if anything is dragging down the 12v.
Check all volts in psu.

There are no secondary fuses (FS301 & F302) the ac from the TX goes straight to the rectifier. The only fuse is a 100mA on the 240v input but according to the service data there are fuses....must be more than one type of main board :aab
I have isolated both pre-amp boards and rechecked the 5v line but it is still 3.6 so the fault is somewhere on the main board.
Just out of interest the PSU is giving voltages of -20.3 and +3.8 in respect to 0v so still hunting whatever is dragging it down.

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sun Jul 31, 2016 4:41 pm
by Cathovisor
Right - assuming L300's fitted, lift one end and see if you get the 12V reappear.

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sun Jul 31, 2016 4:49 pm
by marc
Cathovisor wrote:Right - assuming L300's fitted, lift one end and see if you get the 12V reappear.

That gives me 8.8v

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sun Jul 31, 2016 4:52 pm
by Cathovisor
Better, but not great, is it? Of course, you could connect your bench PSU to the regulator input and see how much current the regulator and processor pull.

If that circuit diagram's right, the mains transformer is 10 - 0 - 10 VAC. Is it really so? Across that bridge rectifier there should be 20V AC. Have you got that? I'm starting to worry that the transformer's got one half of the secondary o/c.

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sun Jul 31, 2016 4:56 pm
by marc
Cathovisor wrote:If that circuit diagram's right, the mains transformer is 10 - 0 - 10 VAC. Is it really so? Across that bridge rectifier there should be 20V AC. Have you got that? I'm starting to worry that the transformer's got one half of the secondary o/c.

21.2vac from the transformer (at the bridge).

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sun Jul 31, 2016 4:57 pm
by Cathovisor
marc wrote:Just out of interest the PSU is giving voltages of -20.3 and +3.8 in respect to 0v so still hunting whatever is dragging it down.

Eh? Hang on a minute...

The raw supply should be plus and minus 12v. So you seem to have the missing bit of the +ve rail added to the -ve rail!

You need to start looking at plate-throughs as well... C308 and C309 should have the ±12V rails on them, with a solid 0V between them.

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sun Jul 31, 2016 5:01 pm
by marc
Cathovisor wrote:
marc wrote:Just out of interest the PSU is giving voltages of -20.3 and +3.8 in respect to 0v so still hunting whatever is dragging it down.

Eh? Hang on a minute...

The raw supply should be plus and minus 12v. So you seem to have the missing bit of the +ve rail added to the -ve rail!

You need to start looking at plate-throughs as well...

Plate throughs.....? ( probably me being thick) links connecting each side of PCB ?

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sun Jul 31, 2016 5:05 pm
by marc
Cathovisor wrote:You need to start looking at plate-throughs as well... C308 and C309 should have the ±12V rails on them, with a solid 0V between them.


Voltages are now
-19.8 / 0v / +3.7

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sun Jul 31, 2016 5:40 pm
by Cathovisor
marc wrote:
Cathovisor wrote:You need to start looking at plate-throughs as well... C308 and C309 should have the ±12V rails on them, with a solid 0V between them.


Voltages are now
-19.8 / 0v / +3.7

So, just to clarify.

You have -19.8 between 0V and the -ve end of C309, and +3.8V between 0V and the +ve end of C308? And yes, by plate-throughs I do mean the links that connect the two sides of the board together. It's behaving as though the +7.5V rail is earthed and the 0V return lifted... :zx:

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sun Jul 31, 2016 5:42 pm
by marc
Cathovisor wrote:So, just to clarify.

You have -19.8 between 0V and the -ve end of C309, and +3.8V between 0V and the +ve end of C308?

That is correct.

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sun Jul 31, 2016 5:50 pm
by Cathovisor
Okay; what about between 0v and mains earth?

Re: Quad 66 Pre-amp stuck in standby

PostPosted: Sun Jul 31, 2016 5:52 pm
by PYE625
"In the amp, a common cause of problems are dry joints, in particular on the through-pcb pin connections."

As I said at the start.

I would carefully re-solder them all and at least you will know they are not playing silly buggers lol.