Citation XX #2 also with issues......

wlhd1610

R.I.P. Penny
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OK ,so I have the other Citation XX amp that was purchased by another AKer from the Lansing site.

It's a good looking and extremely heavy beast!

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Like Wardsweb's it came in a custom box.

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It was purchased knowing that it wouldn't come out of it's protection circuitry.

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After a thorough visual inspection which included checking the main fuses.
Someone has "hamfisted"the left channel fuse cap!

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The fuses were fine and looked to be original.

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I hooked it up to my DBT but this amp requires a BIG dim bulb resistance because of it's two massive power transformers.

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The DBT glowed bright!!
(A 200 watt and 100watt bulb in parallel with an extra 100 watt bulb in reserve.)

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And then settled down after a few seconds as the four 10k caps charged up.

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I believe the "Infrasonic Protection" is a fancy way of saying "excessive DC voltage " on the speaker outputs.

A check of the simply massive speaker binding posts revealed 0.0 VDC on the right speaker terminals but a whopping 15.1 VDC on the left terminals!

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The amp has quite a bit of circuitry packed into very tight spaces so the only way to get readings on the amp boards was to split them apart.
Once you realized that the back plate was just a thin cover it was apparent that this was set up in a modular fashion.

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This allowed the individual amp modules to be separated enough to work on!

To protect all the beautiful black anodized surfaces from scratches I covered them with painters tape.

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I looked over the left channel amp board and didn't see anything burnt,etc.
In-circuit tested most of the transistors and all the outputs while getting acquainted.
It should be noted at this time that there is very little info out there on this amp.
The schematics that we have been able to find so far do not include ANY of the amp board circuitry,making troubleshooting a little harder.

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After finding 486 mv dc on the input signal wiring I isolated it at the amp board to see if it was coming from the headend circuitry or the amp module.

With that done the input of the amp remained at 486 mv while the headend section was 0.0 mv.

Also tested were the main high current dual power supplies for each channel.

They were both nearly identical at 150.1 and 150.2 vdc respectively.

This amp has secondary dual power supplies at 177 and 176 vdc each.

(In reference to each of their isolated grounds they are 75 vdc and 87 vdc.)


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The voltage output of the D3 and D4 bridge rectifiers is 177 vdc each when measured at the output of R1/R3 and R2/R4 respectively.

The right channel +HVR to G is +85vdc and -HVR to G is -87 vdc.

However the left channel +HVL to G is -16vdc and -HVL to G is -72 vdc.

Measurements on right channel Q2 are:
E +85vdc
C +65vdc
B +85vdc

Measurements on left channel Q1 are:
E -15.7vdc
C -15.0vdc
B -15.5vdc


Something is very wrong here!

IC1-4 have the same appearance as mje15033 transistors but not sure at this point if they have a different purpose.

I can swap IC1 and IC2 and see if the issue reverses.

Any input is always and greatly appreciated!!!!

Bob
 
Congratulations on getting such a legendary amp!

Are you familiar with the HK 775? I've heard that a 775 is 1/2 of a Citation XX (less some of the uber quality parts). Perhaps if any unobtainium parts are needed they could be sourced from a working 775.
 
I would not swap parts between channels until you have a better idea of what is happening because swapping a shorted IC or transistor could blow something else. It appears that the low negative supply voltage could be causing the offset at the speaker terminals.

Can the amplifiers be disconnected from +HVL and -HVL? If left channel -HVL then became normal, the amplifier is loading it excessively. If it remains low, then the problem is in the power supply.

>>>IC1-4 have the same appearance as mje15033 transistors but not sure at this point if they have a different purpose.

IC1-IC4 (if I am reading the parts list correctly) are 5 volt positive and negative regulators. MJE15033 are transistors. They are definitely NOT the same.
 
I'd expect some version of a LM317 here...what's the PN of the devices currently in the uit?
 
7A fuses seem low for a massive amp like this, what kind of power does this push? I ask because my WOPL 500w amps run 8A in the speaker lines and and 10A in the power supply. Nice amp, hope you get her fixed!
 
if both HV supplies in the left channel are goofy, then in my somewhat limited experience, you likely have either: separate issues in both supply circuits, a bad rectifier, or bad secondary windings.
 
I was able to find a schematic but it appears to be the same one you have. This, obviously, does not include the actual power amplifier because it would have to have many output transistors in parallel. This appears to be only the power supply, control functions, and the input stages.

It appears that the points marked +/-MVL and MVR are the main power for the output stage. The circuit shown appears to regulate a boosted rail to supply driver stages in order that the output stage can achieve a maximum output voltage swing. So, the points labeled +/-HVL and HVR are the boosted high voltage.

The first place to check would be voltages at MVL and MVR and you report that they are +/-75 volts, so that is good.

For some reason, the +75 volts at +MVL is not getting to the base of Q1. If C13 was shorted, the voltage would be zero, not negative. The fact that this voltage is negative indicates that it is somehow being pulled down by the negative supply. I suspect a shorted Q1 and/or Q3. Diode D9 should be holding +HVL close to the 75 volts at +MVL, so there is a problem here as well.

Additionally, operating the unit in this condition is putting a reverse polarity across C13 and a very high voltage across IC1. This may have blown IC1 and if something has not completely let go, then resistors R1 and R141 should be quite hot. Note that what I have said here assumes that everything is connected on the circuit board. If there are open connections, then the situation is different.

As for the 7 amp fuse comment, those are AC line fuses, one for each channel, and 7 amps would be about right.

What are the voltages if all loads are disconnected from +/- HVL? This would rule out the possibility that the amplifier itself is driving this voltage negative.
 
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I feel like I'm in the middle of an Apollo 13 movie! We got the technical side and then just Dave's Avatar. This place Rocks!
 
Great stuff there Bob. I've been home sick, so very little trouble shooting here. Contact me on parts you may need and I will check my inventory. I have a fair collection of transistors, IC's and stuff beyond the ordinary caps and resistors.
 
:lurk: R1 and R141 are probably toast. Ic1 is a +5 volt regulator (print says UPC7805H) , referenced to the MV+ voltage (output is 5 volts over MV+) Ic3 is a -5 volt regulator, but is being used to track the positive voltage (I would guess to improve start up and shut down functions). Since there are no positive voltages (presumably because of open resistors), diode d11 keeps HV- close to the negative MV- voltage. IC1 is probably toast, but you won't know until you get voltages on it. You won't be able to tell anything about the negative supply until the positive supply is working. Good luck
 
After spending a few hours with it tonight this is what I have done:

Since the voltage at the +HVL output was -16 vdc (instead of the proper +85vdc) in reference to ground I decided to disconnect the +feed to the amp board as suggested.

But first I wanted to know if any sort of load was present.
I inserted a dc ma meter in series and the amp only showed a minimal 4 ma draw so I proceeded.

With the +wire off the +HVL output terminal ,
the reading was 0.0 v so the + side is totally dead.

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Now the voltages on Q1 E , C and B ,which were previously - 15.7 vdc, are now all 0.0 v .

However when looking at the schematic you can see that D1 (the main high current bridge rectifier that supplies the four 10K uf caps for the left channel)
also feeds diodes D9 and D11 through R141 and R143 at the tail end of this circuit.

(D1 is actually mounted at the main filter caps fed by huge #12 ga transformer secondary wires and backfeeds this board with a very small #22 ga twisted pair.)

We should have had some + voltage at D9 but there was none.

I looked for R143 and found it but in R141's location was a solid jumper.

A check of the working right channel side showed the same component layout.

I checked for continuity between D9's anode and +MVL and had none.

I checked for continuity between D10's anode and +MVR on the right side and had 4.8 ohms.

Somethings not right.

It was time to loosen up the board and take a peek underneath.

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The heavy gauge wiring made it difficult to raise more than a few inches but in following the trace from the R141 jumper it didn't go directly to D9.

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The R141 jumper is circled in white while the actual R141 is unmarked and tucked away in between C13 and 14 as circled in black.

Closer inspection with a mirror under the board showed a bad solder joint, plus in addition to that ,the 4.7 ohm resistor is open.

So I'm assuming a possibly bad IC1 placed too much of a load on R141 (which btw does not look scorched/burned at all.) OR did a bad solder joint on R141 cause IC1 to fail OR is there another problem further down the line causing both component failures??

I'll replace the failed parts and then power it up on the franken dbt while monitoring current draw on the +HVL and -HVL supplies to the amp board and go from there.

IC1 is marked NEC 7805S (PC7805H on the schematic) would a digikey p/n MC7805CT-BPMS-ND be a suitable replacement?

As always , thanks for all your help and advice!!!

Bob
 
Holy crap ... it's the stuff of legends. Thanks for the pics ... I have always wanted to see one up close and personal. It's one of the few amps so rare, I have only read about it. I cant add much to this post other than to say I envy you, whatever it takes to get it back on the road.

Hats off to you ...
 
Digi-Key MC7805 is equivalent to any other 7805. I'm guessing at this point that the 4.7 ohm resistors are probably acting as fuses because there is a lot of power here and it could be a serious problem without some sort of short circuit protection. I see no other reason for their existence. The jumper in place of R141 could have been an earlier cobbled repair. Does the board look burned at that location?

You could try connecting the left amplifier to the right channel power supply and see if that is ok. There is a slight risk of damaging that power supply if the amplifier itself had a problem.

Also, replacing IC1, IC3, Q1, Q3, the diodes, and any resistors out of value should be relatively inexpensive. In other words, just rebuild that power supply board. The capacitors are probably all ok. You could check for shorts just to be safe. The diodes could be checked out of circuit with a meter. Replacements shouldn't be critical. 1N100x series with sufficient voltage ratings should be fine.

Neither Digi-Key nor Mouser show anything for the 2SB649 transistors, so that will require a substitution of some sort. Quick research does not turn up anything immediately equivalent but since this is only control for a low current power supply, the main thing would be voltage and power ratings. The originals are rated at Vcbo of 180 volts and Ic of 1.5 amps.


>>>Ic3 is a -5 volt regulator, but is being used to track the positive voltage<<<

No, it is basically a mirror image of IC1 and is regulating the boosted negative rail.
 
>>>Ic3 is a -5 volt regulator, but is being used to track the positive voltage<<<

>>No, it is basically a mirror image of IC1 and is regulating the boosted negative rail.<<

Unless your schematic is different than the one posted, they are not mirror images and the IC3 does not reference the negative rail But it does supply the boosted negative rail). You'd think they would do it this way, but they didn't.
 
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Not only is this the greatest thread ever on the Citation XX, but shows how great AK members are. We have some very smart and talented members, who willingness to help, renews my faith in mankind. It also reminds me of the days when you not only knew all your neighbors, but you helped each other out all the time.

Thanks guys - AK MEMBERS ROCK!
 
I'm on my lunch break so I thought I'd add a few things I forgot to say yesterday.

IC3 on the negative side is a NEC 7905 (print says PC7905S) whereas IC1 on the dead positive side is a 7805.

I believe the solid jumpers in place of R141 and R142 are factory as the original stenciling is next to them.

They were probably post production relocated to a "cooler" position between C13 and C14.

I did test R1 and R3 ,which feed IC1 and IC3 respectively, and they were both fine.

I had considered using the right side power supplies to feed the left amp board but there are just too many separate power supplies/feeds to the each amp board and feedback circuits that it would be a considerable effort (nightmare) to achieve that.

Keep in mind that these are basically two completely independent mono amps on one chassis.

I also didn't want to take the chance of "killing" the working right side power supplies by tying them into the left amp board which still may have issues.

At this point I need to pull together a bunch of parts because it's gonna be a pain to get under the PS board to solder so I'd only like to go in there once!

Thanks again to all!:yes:

Bob
 
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