QRX-7001 Refurb

Would a driver board from a 771 work in the 7001? Have a 771 with a bad variable transformer in the AM tuner.

Was thinking if the 771 board could be used and the bulb was still bright maybe it isn’t the boards that are the problem, and if the bulb dims with the substituted board we’d know I messed up or there is another bad part on the original boards.
 
Pretty sure it's the OTs.

I unplugged the OTs from the board the driver boards plug into, installed the driver boards and flipped on the DBT. Bulb dimmed and the unit came out of protect.

So unless I'm missing something it's the OTs that are keeping the bulb bright, and taking them out of the equation dimmed the DBT.
 
Last edited:
Is the bulb fully bright (hard short) or semi-bright? Still have a feeling that the bias or (more likely) dc offset is out of whack. You can measure the latter from the relay if protection is on.
 
JJCalvillo said:
Pretty sure it's the OTs.

I unplugged the OTs from the board the driver boards plug into, installed the driver boards and flipped on the DBT. Bulb dimmed and the unit can out of protect.

So unless I'm missing something it's the OTs that are keeping the bulb bright, and taking them out of the equation dimmed the DBT.
Click to expand...
My next suggestion would have been removing OTs one channel at a time on DBT to see if you could identify the specific OTs that have issues.
 
JyriK said:
Is the bulb fully bright (hard short) or semi-bright? Still have a feeling that the bias or (more likely) dc offset is out of whack. You can measure the latter from the relay if protection is on.
Click to expand...
I don't think it's a hard short. I'll look at the scheme and see if I can test at the relay.
 
Not sure where to test on F-1461. What about the ends of R7/8/9/10 connected to S01a and SO1b? Haven't tested a relay before.

Have a feeling @JyriK is right about board adjustments. The bulbs dim with the boards in and the OTs out, still, even with new OTs. I've gone through and cleaned all the VRs, so if I can figure out where to get readings at the relay maybe I can adjust to dim the light.

Also, what's the magic number, approaching 0mV?

Since I'm testing at the relay, I should unplug the OTs?
 
Last edited:
The point is to measure with everything installed. Not much use otherwise. Keep it on DBT for now. You have to check which relay pins receive the signal from outputs, and measure each with black lead on the ground. Hopefully there's an trimpot for offset adjustment. I'll check the schem later.
 
Got it out of protect with one board in for the front channels. :beerchug:

I noticed the Tuner chassis was sitting a little back because of a slightly bent tab on the front of the unit and I think it may have been contacting the back of the F-2087 board, or was very close to doing so. I straightened out the tab so the Tuner would sit all the way forward, and bent the plug posts so the board came away from the back of the Tuner chassis. Also going to glue some rubber to the back of the Tuner chassis as a failsafe. Little bit of a flaw in the design.
 
What a day! :no:

Got it to come out of protect with a driver board in the plug for the front channels. So, on the DBT I set the bias and dc. Plugged it into the wall and reset the bias, dc, and 25Vdc to the quad boards, no problems. So I put the second board in the plug for the front again. and did the same, set things on the DBT, then live, and got to the last step, right channel bias at 120Vac and I measured no mA and the light was brighter, not screaming, but it wouldn't come out of protect.
I put the first board in and it would NOT come out of protect with the first board either even though it was adjusted for less then 1mV and 29.5mA in both channels when I took it out.

So I put it on the DBT again and noticed the light flicker and go off. Turned off the DBT and noticed the plug was a little loose, so I tightened everything up and turned the DBT on and the light didn't go on, I put my hand on the plug/cord and it came on. If I moved the cord it would go off. I think the cord/plug is bad so I'm going to replace it.

Also, when I got the first board adjusted I hooked up speakers, but the tuner doesn't work. Before I could hook something up to Aux I noticed the heat sinks were hotter than I'd expect for just tuning bias/dc.

Hopefully the problems are exacerbated by the bad cord and things get a little easier when I take care of that.
 
Last edited:
JJCalvillo said:
What a day! :no:

Got it to come out of protect with a driver board in the plug for the front channels. So, on the DBT I set the bias and dc. Plugged it into the wall and reset the bias, dc, and 25Vdc to the quad boards, no problems. So I put the second board in the plug for the front again. and did the same, set things on the DBT, then live, and got to the last step, right channel bias at 120Vac and I measured no mA and the light was brighter, not screaming, but it wouldn't come out of protect.
I put the first board in and it would NOT come out of
JJCalvillo said:
What a day! :no:

Got it to come out of protect with a driver board in the plug for the front channels. So, on the DBT I set the bias and dc. Plugged it into the wall and reset the bias, dc, and 25Vdc to the quad boards, no problems. So I put the second board in the plug for the front again. and did the same, set things on the DBT, then live, and got to the last step, right channel bias at 120Vac and I measured no mA and the light was brighter, not screaming, but it wouldn't come out of protect.
I put the first board in and it would NOT come out of protect with the first board either even though it was adjusted for less then 1mV and 29.5mA in both channels when I took it out.

So I put it on the DBT again and noticed the light flicker and go off. Turned off the DBT and noticed the plug was a little loose, so I tightened everything up and turned the DBT on and the light didn't go on, I put my hand on the plug/cord and it came on. If I moved the cord it would go off. I think the cord/plug is bad so I'm going to replace it.

Also, when I got the first board adjusted I hooked up speakers, but the tuner doesn't work. Before I could hook something up to Aux I noticed the heat sinks were hotter than I'd expect for just tuning bias/dc.

Hopefully the problems are exacerbated by the bad cord and things get a little easier when I take care of that.
Click to expand...
I was reading a thread that was written by
protect with the first board either even though it was adjusted for less then 1mV and 29.5mA in both channels when I took it out.

So I put it on the DBT again and noticed the light flicker and go off. Turned off the DBT and noticed the plug was a little loose, so I tightened everything up and turned the DBT on and the light didn't go on, I put my hand on the plug/cord and it came on. If I moved the cord it would go off. I think the cord/plug is bad so I'm going to replace it.

Also, when I got the first board adjusted I hooked up speakers, but the tuner doesn't work. Before I could hook something up to Aux I noticed the heat sinks were hotter than I'd expect for just tuning bias/dc.

Hopefully the problems are exacerbated by the bad cord and things get a little easier when I take care of that.
Click to expand...
JJCalvillo said:
What a day! :no:

Got it to come out of protect with a driver board in the plug for the front channels. So, on the DBT I set the bias and dc. Plugged it into the wall and reset the bias, dc, and 25Vdc to the quad boards, no problems. So I put the second board in the plug for the front again. and did the same, set things on the DBT, then live, and got to the last step, right channel bias at 120Vac and I measured no mA and the light was brighter, not screaming, but it wouldn't come out of protect.
I put the first board in and it would NOT come out of protect with the first board either even though it was adjusted for less then 1mV and 29.5mA in both channels when I took it out.

So I put it on the DBT again and noticed the light flicker and go off. Turned off the DBT and noticed the plug was a little loose, so I tightened everything up and turned the DBT on and the light didn't go on, I put my hand on the plug/cord and it came on. If I moved the cord it would go off. I think the cord/plug is bad so I'm going to replace it.

Also, when I got the first board adjusted I hooked up speakers, but the tuner doesn't work. Before I could hook something up to Aux I noticed the heat sinks were hotter than I'd expect for just tuning bias/dc.

Hopefully the problems are exacerbated by the bad cord and things get a little easier when I take care of that.
Click to expand...
I was reading where we have to be careful with the circuits that have the quad ic.
JJCalvillo said:
What a day! :no:

Got it to come out of protect with a driver board in the plug for the front channels. So, on the DBT I set the bias and dc. Plugged it into the wall and reset the bias, dc, and 25Vdc to the quad boards, no problems. So I put the second board in the plug for the front again. and did the same, set things on the DBT, then live, and got to the last step, right channel bias at 120Vac and I measured no mA and the light was brighter, not screaming, but it wouldn't come out of protect.
I put the first board in and it would NOT come out of protect with the first board either even though it was adjusted for less then 1mV and 29.5mA in both channels when I took it out.

So I put it on the DBT again and noticed the light flicker and go off. Turned off the DBT and noticed the plug was a little loose, so I tightened everything up and turned the DBT on and the light didn't go on, I put my hand on the plug/cord and it came on. If I moved the cord it would go off. I think the cord/plug is bad so I'm going to replace it.

Also, when I got the first board adjusted I hooked up speakers, but the tuner doesn't work. Before I could hook something up to Aux I noticed the heat sinks were hotter than I'd expect for just tuning bias/dc.

Hopefully the problems are exacerbated by the bad cord and things get a little easier when I take care of that.
Click to expand...
Last edited: Jun 5, 2016
•
2.jpg

Trnsfmr
Well-Known Member
• Mar 25, 2016
• Add bookmark
• #2
Fixing it
So... if you're now sure the outputs are good, plug the board in and see how it is. We like to monitor bias when we do this. If it's still broke... well... now you have to fix it.

With the 6,7,8-9001 models DO NOT, and I repeat DO NOT use a dim bulb tester or a variac, ever, to bring up the power slowly. If you do this, the practically irreplaceable IC's on the quad processing boards will blow. They want to see 25v. and nothing else.

If the outputs transistors were bad, check the last four driver transistors for that channel (TR11-14) (TR15-18). These are most likely culprits + TR5,6. If the output transistors were good, you will need to check all the transistors for that channel on the board. Trying to take readings while it is operating is useless, because of the aforementioned feedback circle effect. Some of them you can check in circuit (and unpowered) and some you cannot, because there are too many connected to each other. You must find out what is wrong.
 
Wow, that ain't good! I always put a unit on the dim bulb to make sure it's safe to plug it into the wall.

I wonder if the QRX-X001 models have the same chips on the CD-4 boards? If not, you could test with a DBT with the QS/SQ boards pulled, and possibly the CD-4 board that plugs in at the right front of the Tuner module could be pulled if the sensitive chip was on it.

Supposed to see a new cord today.
 
Installed the new cord and pulled the QS & SQ boards. Tested both driver boards in the plug for the front channels and both brought the unit out of protect.

Then I put a board in the plug for the back and got a spark. So something wrong on the back channels between the board and the OTs.

No doubt I now have a problem on the board I plugged in for the back channels, and/or the new OTs. :no:

Going to test the plugs to OTs and see if there's a problem there. Good news is I bought 10 of the OTs so I have two backups.
 
Tested the fuses on F-2456 and the 7A fuses #s 5, 7-9 (no fuse at #6) were all toast. They tested good previously, so I believe the "spark" was the flash from those fuses blowing.

The 1 amp fuses on the board were all good, as was #10.

Going to get fuses.

Any advice would be appreciated.
 
I restored a QRX-7001 a while back, and I used a DBT to bring it up. There was no harm done to the quad ICs, and the unit sounded really good. I wish I still had it!
You should not adjust the bias while on the DBT, because when you go to full wall voltage, it will be much higher You need to be able to power up from the wall before adjusting bias. The DBT gets you safely to full wall voltage. If you get more than a dim glow, you have a troubleshooting problem. A bright glow is a hard short. There are no “soft shorts”. Until you only get a dim glow, stay on the DBT.
 
No problem adjusting the bias with DBT, as long as one knows it is going to be higher without it... The advice was for checking if bias was too high causing the semi bright bulb.
 
You must log in or register to reply here.
Back
Top Bottom