AU-999 Restoration & Modification

[Hipocrates]

OK, so we got this.

- Transistors on right place and correct pinout.
- Solder work cleaned .

What do you think guys?
Can it be that ZTX devices on TR11 and TR13, do not work?

Check wiring to F1277, 1231

 

[Hipocrates]

 

[leray1]

I haven't tested the cleanup work, yet. I'm still waiting for the deoxit in the board slots to dry. I'll update ASAP.

 

[kevzep]

For the amplifier to behave the way it is, there has to be a transistor incorrectly mounted, OR there is a NPN where there should be a PNP etc...
Have you checked the 2SC281 (Bias transistor), you can mount something else in there like a KSC1845 , the spec's for that transistor are not critical for testing, you might even be able to put one of those ZTX in there, that will do for the testing.
Check the pinouts of the transistors and make sure you have it right, I have seen it wrong sooooo many times....
Don't worry about the deoxit drying, just wipe it or blow it and you are good to go.....I'd never get anything done if I waited for deoxit to dry...

 

[stereofun]

Good advice from AnalogueBen - On my 999, after a full rebuild, I knew everything was correctly mounted, yet one channel remained dead. I did a thorough visual inspection and found a hairline crack in the trace 1-2 mm away from a solder joint. In other instances I've had a seemingly good solder joints covered a lifted trace, not making proper connection...and the list goes on. Whenever we solder away on these old boards.... stuff can happen.

I notices from one of your earlier post that you got a pretty decent offset and a high bias of 50'ish. Then in the next post you were suddenly quoting crazy high mV off the emitter resistors ? I highly highly recommend that at this stage you only set bias pr. service manual aka across the empty fuseholder looking for mA. The emitter resistors are my preferred method to set bias - however, they can be real tricky to get a good reading on sleeved resistor legs - I even use tiny spring loaded hooks, even then I get weird readings unless I have perfect contact - so here in the "newbie / diagnostic phase" - I'd be hesitant about introducing another way of measuring and potentially adjusting VR803 on a false reading.

Have you confirmed that you have 1k Ohm as VR803 - You can measure ohm on the two outer legs and check.

 

[gslikker]

I haven't tested the cleanup work, yet. I'm still waiting for the deoxit in the board slots to dry. I'll update ASAP.

use paper, and take it out


I did not see anything in the topic about the protection circuit.
You can take it out of the loop by taking out the speaker fuses, if it was not disabled already.
If it is in and it engages because of a moment of DC, it will stay alive, shorts itself and compromise your measurements until power off....

You also can consider blown fuses and resistors instead of the power fuses for testing.


Further, it always helps making big printouts of parts of the schematic, and write the voltages measurered at some specific situation down in the schematic.
Sometimes that way you suddently see something "impossible" which can lead you to solving the mystery.

 

[leray1]

I just tested again, the bulb pulses about 5 times before settling, bias is still high. Both boards installed separately give the same result (didn't check bias separately).

I checked and rechecked pinouts on the transistors. If something is wrong, I don't see it.

The amp worked fine before the work, although I never checked bias, would the bias transistors still be suspect? If they are, and I put in something else, how do I connect it to the metal sleeve that connects to the outputs?

both VR803s are 1Kohm - confirmed on multimeter.

I removed the protection circuit last night right before attempting to set bias and offset.

I will check bias via the SM method later. I'm in the middle of a honey-do right now.

 

[leray1]

SUCCESS! After kevzep recommended, and Hipocrates urged, testing the 2SC281s, I did and found them to be bad. I put a couple of ZTX694Bs in their place and the bulb lights up and goes out, just like with the boards removed.

Should I replace the 2SC281s with the same thing or is there a better replacement?

 

[Hipocrates]

I've read that you can use KSC1845 or even 2N2222 stuff, let's see what the more experienced fellows say.

 

[stereofun]

SUPER !! - just surprised both were bad at the same time. Ksc1815 is a good replacement, rather than overpay for some eBay originals or... fake. I saw an AK'er re-use the old 281 sleeves and long insulated legs. Maybe Kevzep or Hippocrates remember that post ? The neat thing was that with the new transistor inside the old sleeves (I think some resin was used to fill out gaps) - the new tranny would fit perfectly into the heatsink sleeve as before.

 

[kevzep]

SUCCESS! After kevzep recommended, and Hipocrates urged, testing the 2SC281s, I did and found them to be bad. I put a couple of ZTX694Bs in their place and the bulb lights up and goes out, just like with the boards removed.

Should I replace the 2SC281s with the same thing or is there a better replacement?

I've used KSC1845 for bias transistors in a recent restoration, its just what i had on hand, the amp is in daily use and working fine 12 months later, you do have to squeeze the metal tube for them to fit, and extend the legs with wire, and heat-shrink the exposed legs on the transistor so it doesn't short out on the metal tube or itself....

 

[leray1]

I have KSC1845's on hand but they're bound for another board. If I use them I'll have to place another order anyway. So, I'll order some KSC815's.

I'll move on to the other boards in the meantime.

 

[leray1]

Finished up the Head Amp., Tone Control & Driver Boards today. My Head Amp. board has C621 which wasn't on the parts list that I used to order all my parts. I'm replacing it with a UHE1J330MED (33µF 63V). I ordered one today along with the bias transistors. I'm hoping to get to the three Ripple Filter boards after work one day this week. All that's left after that will be the Bass EQ and Pre-amp mods (I'm a little intimidated by these as the tight spaces will make it fiddly) , then dialing it all in.

 

[leray1]

I ordered new outputs based on the parts list from this thread.

Drivers
TR815-16 Replaced with onsemi MJE15032 (NPN) x 2
TR817-18 ----------------------------- MJE15033 (PNP) x 2

What I got is what is pictured. What are the proper replacements?

 

[Hipocrates]

What are the proper replacements?

Those are the proper replacements for your drivers transistors.
TO-66, are almost unobtanium or very expensive or/and fake, so what you do is to mount TO-220 devices.
In your unit your driver transistors (TO-66) are fine, so you can left them be.

The outputs are the transistors (TO-3) mounted on your heathsink, which I believe are MJ21194G now.

 

[leray1]

I'm wrapping up the preamp mod right now and have a question about the resistor that is put on the trace side.

On this post there is the attached pic for the schematically challenged where it looks like one leg of the resistor is on the Emmitter of TR705 and the other is on one leg of C721 (green mylar). Am I looking at the pic wrong? From what I understand, the resistor should go on the same joints as the orange capacitor. i.e., one leg on the Base and the other on the Collector of TR705.

 

[leray1]

Never mind, I figured it out...pics shortly.

Preamp mod done. The new resistors blend right in. Looks like I have a couple of legs to trim

 

[stereofun]

I ordered new outputs based on the parts list from this thread.

Drivers
TR815-16 Replaced with onsemi MJE15032 (NPN) x 2
TR817-18 ----------------------------- MJE15033 (PNP) x 2

What I got is what is pictured. What are the proper replacements?

If your outputs and driver's are originals, I'd absolutely keep them. If your outputs are onsemi Mj21194's then, you can still keep your original driver's - infact that is the best for now, otherwise you have to modify the new driver a bit. I am probably the only one who replaces driver's when replacing outputs, so that they are onsemi all the way through.

 

[leray1]

If your outputs and driver's are originals, I'd absolutely keep them. If your outputs are onsemi Mj21194's then, you can still keep your original driver's - infact that is the best for now, otherwise you have to modify the new driver a bit. I am probably the only one who replaces driver's when replacing outputs, so that they are onsemi all the way through.

Yes, I replaced the outputs with onsemi MJ21194. The drivers will stay.

 

[leray1]

Working on the Ripple Filter Board, I ordered a KSC5603DTU as a replacement for TR001. Has anyone ever changed this transistor? Should I?

Also, D002 is three legged. How do I connect the 1N4004?