QRX-7001 Refurb

JJCalvillo said:
When you say 4 channel discreet is that the same as CD-4? If so, is that the shielded board behind the Tone Control and the PS/Filter Boards?
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On the 7001 CD-4/4 channel discreet are the same setting. You'll want the source selector set to AUX with nothing connected to the AUX jacks and volume at minimum.

The quad boards do not pull significant current.

DC offset and bias are set with VR's on the driver board, so you can't set those without the driver board in. If it does not come out of protection with the driver boards in, you won't have any signal at the speaker outputs to set the offset.

JJCalvillo said:
Would pulling the quad boards pull down the bias? It stays in protect w/the QS/SQ boards in, comes out of protect when I pull those boards.
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You said it came out of protection with the quad boards out, but without the gray wire disconnected, but this is the same response with the quad boards in. So, the real test is to connect the gray wire and with the quad boards out, driver boards out, see if it comes out of protection and/or you get a dim DBT.
 
KeithD said:
On the 7001 CD-4/4 channel discreet are the same setting. You'll want the source selector set to AUX with nothing connected to the AUX jacks and volume at minimum.

The quad boards do not pull significant current.

DC offset and bias are set with VR's on the driver board, so you can't set those without the driver board in. If it does not come out of protection with the driver boards in, you won't have any signal at the speaker outputs to set the offset.


You said it came out of protection with the quad boards out, but without the gray wire disconnected, but this is the same response with the quad boards in. So, the real test is to connect the gray wire and with the quad boards out, driver boards out, see if it comes out of protection and/or you get a dim DBT.
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No it wasn't coming out of protect with the boards in. Also, I soldered the gray wire in w/the quad boards out and it comes out of protect and the bulb be dim in CD-4 mode, so the QS/SQ boards seem to be the problem.

Since the F-2087 board has so many hit list transistors I'll change those out and see what it does then.

Thanks for the advice amigos!
 
JJCalvillo said:
No it wasn't coming out of protect with the boards in. Also, I soldered the gray wire in w/the quad boards out and it comes out of protect and the bulb be dim in CD-4 mode, so the QS/SQ boards seem to be the problem.

Since the F-2087 board has so many hit list transistors I'll change those out and see what it does then.

Thanks for the advice amigos!
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OK, thanks for the clarification. That's good progress. :thumbsup:

Have you restored the driver boards yet (replace fusible resistors, bad diodes, differential pair transistors)?
 
KeithD said:
OK, thanks for the clarification. That's good progress. :thumbsup:

Have you restored the driver boards yet (replace fusible resistors, bad diodes, differential pair transistors)?
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Yes replaced all the transistors and caps and the 10 ohm, 1 watt fusibles which were headed to 12 ohms. Tested the other fusibles and they were good.
 
JJCalvillo said:
Yes replaced all the transistors and caps and the 10 ohm, 1 watt fusibles which were headed to 12 ohms. Tested the other fusibles and they were good.
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OK, if it were me I'd try putting the driver boards in with the quad boards out. If it comes out of protection and you get a dim bulb, you can be pretty confident the problem is on the quad boards.

Long term, I'd replace all fusibles on the driver boards. No reason not to. You'll also want to replace D05 and D06. They are VD1212 and are known to go bad. Replacement is two 1N4148 in series. You just want to make sure one of the driver boards is not the source of any problems.
 
Refurbed F-2087 and tested it and the unit takes a few seconds longer to come out of protect. Dim bulb

If I put in F-2088 (original parts) the bulb is slightly brighter and it DOES NOT come out of protect (F-2087 still in).

Brighter bulb with the driver boards in, stays in protect as well.
 
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Just in case there is still something amiss on F-2087, try putting just F-2088 in with 2087 and driver board out and see if you get dim bulb and it comes out of protection. There are no discreet transistors on 2088, so if there is a fault on that board with an IC, I know of no source for replacement ICs. The schematic in the QRX-6001 service manual has voltages for F-2088 at various points, so at least you can measure voltages. But if you get a dim bulb with 2087 out/2088 in, then 2087 might be feeding bad voltages to 2088 - you can check voltages on that board against the schematic in the 6001 manual. While you are at it, check PS voltages to make sure nothing is amiss there. In particular, supply voltage to the quad boards needs to be 25 V.
 
@KeithD , This morning I tried F-2088 in alone and it did come right out of protect, so I tried both in again w/both boards and the relay didn't click, but the bulb is barely brighter.

I think there still IS a problem with F-2087. After doing the DBT a few times w/F-2087 in, it isn't coming out of protect. Replaced all the caps and all the transistors yesterday

I did find two of the three ICs (HA1327) at Ceitron and got a couple just in case. No doubt the third IC is unobtainium and is the QS control.

Also get the feeling the protection circuit is struggling.

I will get voltages sometime today, got a guy coming over for some speakers and then have a geetar lesson.
 
I used 5 film caps 1, 2.2, 3.3 uf/50v on the F-2087 when I recapped. Would that cause problems? Went back over the boad and according to the screen all the transistors are in right, as well as the caps. Caps were marked against on edge of the board, and the screen agreed with the marks in all cases.
 
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@KeithD do you know where the voltage from the PS comes in for F-2087 and F-2088?

About to start checking V on F-2088 as it doesn't make the bulb any brighter and the unit pops outta protect pretty quick when the board is in.
 
JJCalvillo said:
@KeithD do you know where the voltage from the PS comes in for F-2087 and F-2088?

About to start checking V on F-2088 as it doesn't make the bulb any brighter and the unit pops outta protect pretty quick when the board is in.
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I've not worked on a 7001, and the PS is different than the 8001/9001. From what I can tell from the schematic, F2428 is supplying 25V (red circle in image), which is controlled by VR01 on that board (blue circle).

F-2428.png

The 25V output is marked 40 in a circle, which is shown on F-2088 as connecting at pins 1 & 5.

F-2088.png
 
Adjusted VR01 to get 24.8Vdc at the pin 5 end of the first resistor on F-2088. Then dropped in F-2087 to see what happens w/the V correct and both boards in through the DBT, and... :beerchug: it came out of protect with the bulb dim. Do I dare give it a test straight into the wall?

VR01 is fully clockwise/minimum so I have to clean it and see if that changes anything, or think about a new VR. Refurbed that board w/caps and transistors. Used the heavier weight transistor KSC2690 for TR03, vs KSC945C. Wonder if that was overdoing it?
 
Cleaned VR01 and have it 2/3 to 3/4 clockwise set to 22.4 Vdc on the bulb. Unit comes out of protect in 3 or 4 seconds.
With both F-2087/2088 connected.
 
Moving on, if the bulb doesn’t dim next time w/ driver boards in, is it possible one or more of the OTs is bad? Tested them w/ Peak DCA55 and they all tested ok though the Hfe was pretty low, 12 on one OT, and nothing above 28.

TR13/14 on the driver boards have a heat sink and a can transistor (varister?) mounted to it. Sink is isolated on the board, not to any trace, and there was no mica between any of those 4 transistors and the sinks when this arrived. Figured no mica was alright since the sink was isolated, not grounded.

EDIT: With the varistor mounted does that require mica between it and the transistor’s sink?
 
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Went ahead and put mica and past between the transistors and varistors/heat sinks on the driver boards and it didn't dim the bulb. Didn't think it would because the screws don't have the plastic washer/separator keeping the screw from making a connection anyway.

Do I try new OTs with the DBT?
 
JJCalvillo said:
Adjusted VR01 to get 24.8Vdc at the pin 5 end of the first resistor on F-2088. Then dropped in F-2087 to see what happens w/the V correct and both boards in through the DBT, and... :beerchug: it came out of protect with the bulb dim. Do I dare give it a test straight into the wall?

VR01 is fully clockwise/minimum so I have to clean it and see if that changes anything, or think about a new VR. Refurbed that board w/caps and transistors. Used the heavier weight transistor KSC2690 for TR03, vs KSC945C. Wonder if that was overdoing it?
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Well, that's good progress. Don't know if your replacement transistor choices are correct, as I have not replaced those particular transistors before. You'll need to confirm by looking at the spec sheets. Be aware that when you power up the unit without DBT you will need to adjust the voltage again, as it will likely be higher than 25V on line voltage. So, make sure your trimmer has some room to dial down the voltage. If it does not, then I'd suspect those are not the right transistor replacements.

If you get a dim bulb and it comes out of protection with everything in except the driver board, that points to a fault on the driver board. Probably would be best to list what you have replaced and what the replacements were.
 
See post #22.

There are multiple lists of transistor replacements on AK I reference, if the original isn’t on the list I do a search and usually find multiple threads and suggested subs.

I’ve gone back over the boards two or three times and I’m still clueless.
 

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