Another Kenwood KR-9600 Power Supply / Protection Mode Repair

bhuskins

Super Member
I have a KR-9600 recently acquired that remains in protection upon power up and the relays do not engage. So I've read most of the threads about issues to look for and I'm not finding an obvious repair. Most all of the voltages are within a reasonable tolerance when compared to the schematic EW has posted that shows the power supply boards A and B and the relay board.

All of the Power Supply Board B voltages read properly.
Most of the Power Supply Board A reads properly (exception below)
The relay board shows pin2 less than 50mv and pin 7 at -8.2v which appear to be correct.

On Power Supply Board A all of the voltages around QK2, QK3, QK5, QK6 are correct as well as most of the pins that have a listed voltage which are pins 23, 15, 28, 33, 6/14, 17, 18, 19, 21, 7/22, 3, 9, 11 and 1

Pins with issues are
pin 30 reads fluctuating between 57v~59v (should read 67v)
pin 25 reads fluctuating between 57v~59v (should read 67v)
pin 10 reads -30.5v (should read -35v)

When reading voltages around QK7
C reads 13v (should read 0v)
B reads 36v
E reads .148v (should read .15v so that's ok)

Also both sides of Rk29 (1M resistor) reads 36v and the anode of Dk6 diode reads 13v and the cathode reads 36v. Also the side of Rk22 (220K resistor) that’s supposed to read 12v reads 36v and the other side reads 13v and should read 0v. I haven't measured the other 6 transistors on the board yet because of the issues discovered above. Rk22, Rk25 and Rk29 don't read correctly in circuit but I haven't removed them yet to confirm they are good or not. They look perfectly fine but looks can be deceiving I guess. Finally, diodes Dk6 and Dk7 test fine in circuit with a diode check.

Any ideas on what needs replacing? Maybe EW can chime in?
 
I followed most of that, and rather than dissect it all, some clarification is needed.

1. You say "The relay board shows pin2 less than 50mv and pin 7 at -8.2v which appear to be correct.". On the relay board schematic, pin 7 is incorrectly shown twice...Pin 2 is the input for the right channel, and pin 3 the input for the left channel (looking at the board, not the schematic). Pin 3 of the board is labeled Pin 7 on the schematic, in addition to the correct Pin 7. Anyway, the board should be properly silkscreened, and pins 1, 2, 3, and 4 should all be inputs and outputs from the speaker relay. So check pins 2 and 3 to see that they are low enough to prevent the protection from causing a fuss.

2. On Qk7, it cannot have a difference of more than about 0.7V between the base and emitter, or else the transistor is dead. I dunno why the scat is marked with the '12V' arrow right above Qk7, but if you follow the trace back you'll see it connects right to the output of the positive regulator on Power Supply (B), and thus a nominal reading of about 34V is what should be seen.
 
Relay board readings per silk screened locations...

pin 1 = -1.1mV
pin 2 = -1mV
pin 3 = 70.3v
pin 4 = 118 mV
pin 5 = -38mV
pin 6 = 8.4v
pin 7 = -8.4v
pin 8 = -8.4v
pin 9 = 7.8 mV
pin 10 = 1.2mV
pin 11 = -1.2mV

Give me some good news about the Amp board please:worried:

We can address Qk7 I suppose after we address the problem above...
 
Give me some good news about the Amp board please:worried:
There are failure modes that can result in such a reading, but the most likely one is that the output module on that channel is toast.

You can contact eBay seller pc_317 (In Israel) and ask if he has some (his will be labeled Sanken).
 
2 questions...what's the best way to investigate that amp board and module? and if I completely remove that amp from the circuit would that allow me to further test the protection mode on the amp while waiting on a module if need be? Or does it require minimal feedback from the amp module to work.
 
I sent pc_317 a message...he shows some on italy ebay site but none currently on USA ebay, not sure if they are still listed or not though.

Are there other options on building an alternative?
 
No reason to remove the whole board...it's wire-wrapped anyway and you DON'T want to be fooling with the wire-wrap.
 
That's what I figured...I'd never unwrap anyways and just unsolder the pin(s) if necessary (or when I restore the board with new caps). Once removed is there any 100% way to test the module to determine if it's good or not?
 
The 9600 manual has an internal schematic to show what the module consists of, and you can do some basic checks from there.
 
So it looks like some basic diode tests could be performed between 3-8, 4-6, 6-7, 1-3, 3-10. It also looks like resistors are involved in all of those pin to pin layouts so I'd assume results could be iffy. Am I better to more thoroughly test it before removal from the amp board? I'm just trying to 100% confirm the module is bad before discarding the module being that it's fairly scarce. Or, should I look at what other causes could have pin 3 on the relay board reading 70v to rule out all other possibilities. Thoughts?
 
If your soldering/desoldering skills are decent, no big deal to remove the module. More than likely you'll find a short between 1 and 5, or 5 and 10.
 
So after removing te power module on the left channel pins 1 to 5 are definitely shorted and pins 5 to 10 are not shorted.

Also, with only the left module desoldered from the amp board the unit comes out of protection when powered on and the right channel as well as all other functions are working like a champ. So, at minimum I'm now on the hunt for a replacement TA-200W module. The last thing I would want to do is locate a hard to find amp module and solder it in to then fry it upon power up. What are the common reasons for these modules going bad? Should I be checking all the voltages on the amp board now with the module removed? Other tests I can do? Just looking for the safest way to test and install a "new" module once one is located.
 
To protect the new module, build a DBT. My own is even simpler than these, with no ON/OFF switch (less parts to break, in my estimation). A 100W bulb is appropriate. Ought to go bright, and quickly dim down as the big caps charge.

When I rebuild a 9600 amp section, it gets all new caps and all new semiconductors. Particularly, Qe6, 7, and 8 are undersized for the job. The Sanyo 2SA1209 and 2SC2911 (B&D Enterprises) are perfect for this position. For Qe1, 2, 3, 4, and 5 the Toshiba 2SC2240BL and 2SA970BL work great.

I also like to dump the two tantalum caps at the input and install a nice 1.5µf 250V Panasonic polypro film cap, or a 2.2µf stacked film.
 
I was able to find a new amp module so I'm going to rebuild both amp boards.

Here are the parts I plan to use for the amp boards being that I can source everything from mouser (local to me) and from what I have on hand.

Any issues with the parts list?

Qe1, Qe2 2sc1345 - KSC1845
Qe3, Qe4, Qe5 2sc1775 - KSC1845
Qe6,Qe7 2sa912 - KSA1013
Qe8 2sc1885 - KSC2383

Ce2, Ce13 1.5uf 250v - Panasonic 1.5uf 250v Poly Film Cap

Nichicon PW Caps for the rest
Ce3 220uf 10v
Ce6, Ce7, Ce11 10uf 50v
Ce9, Ce10 3.3uf 100v
 
With no offset adjustment available, keeping base current to a minimum on the input pair is critical in reducing offset. The high gain versions (the 'U' devices) of the C1845 are gone, the 'F' gain code is the only one now available. While these would certainly work, getting offset below 25mV might be tough with them, thus I recommended the 2SC2240BL for Q1 through Q5. A number of them might have to be bought to find a suitable matched pair.

The TO-92's you list for Qe6, 7, and 8, the A1013 and C2383, suffer from the same issue as the original transistors; they are undersized for the job at hand. A tougher TO-126 is needed here, and the Sanyo devices I listed in my previous post are the ideal replacement.

All these parts are available at B&D Enterprises.
 
What about KSA1220A/KSC2690A for Qe6~8? (I have those as well)

VCBO: - 160 V
VCEO Max: - 160 V
VEBO: - 5 V
Collector-Emitter Saturation Voltage: - 0.4 V
Maximum DC Collector Current: 1.2 A
Gain Bandwidth Product fT: 175 MHz
Maximum Operating Temperature: + 150 C
Package / Case: TO-126
DC Current Gain hFE Max: 320
 
Not the ideal part, but should be OK. I have those Fairchild parts as well, but instead recommended parts that I have experience with in this application.
 
I got ya...I order the parts from b+d...while I wait on them I figure I may experiment with the other options to see how they perform against the final solution.

I'd assume if using KSC1845 in Qe1~5...I'm looking to use the highest hFE parts and after install looking for an offset lower than 25mV (as close to zero as possible.)

With, Qe6~8, where I'm risking it is when stressing the amp with the smaller parts installed they might fail and the a1220a/c2690a although a tougher to-126 the hFE is slightly lower than the suggested parts...same risk with the T0-126 or just more of a preference and like you said, recommending a known solution you've had good luck with?
 
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