QRX-8001 Tech Advice Request

[quadralizer]

Hi,:friday:

:sunHappy New Year,May the FOUR'se be with you:sun

I have some QRX-8001 technical Q's
Hope there's someone out there that can answer these for me.

I don't YET have a service manual for the 8K1, if anyone has a scanned manual/schematic they can email me, I'd be very grateful.

I do though have a lot of experience in Pro-Audio-Video Servicing, so I'm not @: phased (+or-90°) by the famous bad pass through joints on the double sided 2634 pcb which holds the mere five way switch bank, after all most mixing desks I've seen have more complexity in just one channel! .. never mind the other 96 ++... Anyway 10mins with a hammer .. err I mean.. hot :flame iron and those are fixed, along with some hairline cracks in the print tracks.

So now down to the business in hand .....

I have searched the board and read all the posts I can find, but can't find
any to conclusively answer my questions which are as follows:

1) Power Supply

a) What is the correct voltage marked in the manual?

I have seen it stated on here or elsewhere:
Adjust board F-2087 25v @pin 5 with VR01 on Power Regulator PCB
F-2639 I assume that's measured WRT chassis?

I found the initial voltage was set to 19.98v (either on purpose or
because it's drifted)

At this voltage the chips on F-2087 & F-2088 boards run at the expected
temperature, i.e. just warm to the touch.

However once the Voltage is corrected to the stated 25v
(assuming this is correct) the chips heat up dramatically,
and whilst still seeming to work ok, they rapidly become much too hot
to touch comfortably.

Is this normal at this supply voltage? or
Is the supply actually supposed to be 20v?

2) CD4 DEMODULATOR PCB F-2589 Q's
NOTE: I have a F-2589 in my 8K1 NOT a F-2590

a) What is the correct Alignment & Calibration Procedure for the demod.

b) Is it not a F-2590 that is usually fitted in the 8/9k01's
What's the difference, I assume it's minor cct & print revisions.
The 2589 HAS the later CD4-392 chips on it.

Is it possible to attain :worthy'Holy Grail' status with this variant PCB.
If so what (if any) mods are needed to be made. And how does the
alignment differ from the standard way as per in the manual

c) CD4 Carrier Detection

I've not had the opportunity to test out CD4 till now.

I am rather surprised to find that any tone signal over 15Khz I inject into the Phono i/p lights the 'CD4Radar' led.

I would have thought that the radar would only light when the demodulator detected a carrier tone that was within x% of the carrier centre frequency,
as is the case with the 19Khz pilot tone for FM Stereo.
Is this normal? or maybe this behaviour is due to a fault or misalignment?

In respect of the turning on of the radar light, is the presence of a valid carrier normally detected by each channel independently or just one channel.

Also is it normal to hear audible HF, which I assume is carrier spurie or subharmonics of, as soon as the blank lead-in groove track hits the carrier Pre-Roll? or during inter-track banding.

I'd be interested to have any information on the precise detail of CD4 spec's carrier freq, modulation etc.
I've done lots of searching the web and despite the ability to unusually find the most obscurest of things CD4 technical information seems to be totally absent.

3) Blend Resistors

Location & component ref please


Ok, over to you guys .... the ones that know that is


John

[email protected]

 

[JonUrban]

I think this is one of the posts that got "lost". Yesterday there was a reply from quadralizer wondering why no one has replied. I then replied to that post suggesting that quadbob may be away for the holidays.

Both of those posts are now gone. Very strange indeed.

Can anyone here help out John???

:-jon

 

[Malcolm2010]

I think this is one of the posts that got "lost". Yesterday there was a reply from quadralizer wondering why no one has replied. I then replied to that post suggesting that quadbob may be away for the holidays.

Both of those posts are now gone. Very strange indeed.

Can anyone here help out John???

:-jon

I have a QRX8001/8001 manual as a pdf file that I can email to John, also I found the voltage should not be measured at pin 5, on the schematic I have for the qs decoder, pin 5 relates to the SQ section, I will check when I get home from work. When I set up my QSD-2, I measured the voltage just after the regulator to ensure it was correct. The chips do run fairly warm.

Malcolm

 

[quadralizer]

.... Both of those posts are now gone. Very strange indeed.

Maybe they were out of phase and cancelled each other? :ugham:

Hope the server probs are now fixed.
Computers eh? ... about as useable as mis-aligned CD4!

 

[quadralizer]

I have a QRX8001/8001 manual as a pdf file that I can email to John, also I found the voltage should not be measured at pin 5, on the schematic I have for the qs decoder, pin 5 relates to the SQ section, I will check when I get home from work. When I set up my QSD-2, I measured the voltage just after the regulator to ensure it was correct. The chips do run fairly warm.

Malcolm

Congratulations Malcolm You Win .

Thanks for that if you can email me the pdf that would be great.
​

I measured the voltage just after the regulator to ensure it was correct..

That's were I asumed it should be measured from, but when it was set to 25v @ the Reg Pcb the chips went from just warm to untouchable .. now where did I put that rarely used Dmm Temperature Probe???
​

The chips do run fairly warm

To be on the safe side maybe I'll investigate adding a heatsink.
Maplin do a mini Stick-on DIL Heatsink.
I'll see if that works before I consider bolting a nitrogen cooled pentium class fan to each chip !
we don't want Mcdonald's 'deep fried' chips do we!
​

 

[Malcolm2010]

Ahh, another Uk Quaddie !!,I live in the North East near Durham.

I will email the pdf file tomorrow from Work ( MUCH faster link ) so it should be there sometime about 12 ish. Be warned it is about 6 Meg, so be prepared for that. Unfortunately it does not have tha all important decoder sert up information, but I have the application not an-052 as well, so I will send that.

Malcolm

 

[The Quadfather]

I can answer one of those questions. A properly operating PLL circuit, which the CD-4 demodulator is based on, will lock to a carrier that falls within it's lock range. It's oscillator will follow the input signal frequency, controlled by a control voltage produced by a detector that determines the phase difference between the incoming frequency and that of the oscillator. (this is usually all going on inside the chip, with points measurable on the pins of the chip.) This action is very quick and it is that control voltage moving up and down as it tracks the frequency of the incoming subcarrier, and controls the oscillator, that is used as the audio output of the circuit, since it is an exact replica of the modulations of the subcarrier. So, it is that ability to lock on and match the frequency of the incoming signal that makes it work. Splatter is caused when the subcarrier is weak, and the oscillator tries to lock on to the adjacent audio at the high end of the audible band, which of course, drives it nuts. This happens when the stylus fails to track and the subcarrier collapses momentarily. The oscillator will lock on to the strongest signal present. I hope that explanation clears it up for you. Happy Listening!

The Quadfather

 

[QuadBob]

Hi,:friday:

1) Power Supply

a) What is the correct voltage marked in the manual?

I have seen it stated on here or elsewhere:
Adjust board F-2087 25v @pin 5 with VR01 on Power Regulator PCB
F-2639 I assume that's measured WRT chassis?

I found the initial voltage was set to 19.98v (either on purpose or
because it's drifted)

At this voltage the chips on F-2087 & F-2088 boards run at the expected
temperature, i.e. just warm to the touch.

However once the Voltage is corrected to the stated 25v
(assuming this is correct) the chips heat up dramatically,
and whilst still seeming to work ok, they rapidly become much too hot
to touch comfortably.

Is this normal at this supply voltage? or
Is the supply actually supposed to be 20v?

The correct pins are Pin 1 and Pin 7......I just can't remember which is which off the top of my head between 2087/2088.

Measure the voltage with the pcbs installed (underload) for 25vdc at the power supply or Pin 1 or 7.....of whichever pcb! Email me and I'll nail the answer for you. Your heat problem most likely is due to a poor (-) return connection which travels all over the function select pcb and through the infamous "pass-through" joints. Clean that up first to be able to read proper voltages!

2) CD4 DEMODULATOR PCB F-2589 Q's
NOTE: I have a F-2589 in my 8K1 NOT a F-2590

a) What is the correct Alignment & Calibration Procedure for the demod.

There isn't one........its most likely hiding with the Sansui addendum bulletin that also details the Vario-matrix calibration! Never found a copy!

b) Is it not a F-2590 that is usually fitted in the 8/9k01's
What's the difference, I assume it's minor cct & print revisions.
The 2589 HAS the later CD4-392 chips on it.

Is it possible to attain :worthy'Holy Grail' status with this variant PCB.

No difference I immediately remember.......I'll have to take a look. HG should be completely obtainable........

If so what (if any) mods are needed to be made. And how does the
alignment differ from the standard way as per in the manual

patent pending..................

I see that you're across the pond........
so email me and I'll help where I can.