SPEC-2 Refurb Help Please

Long time listener, first time caller...

I've been lurking here for quite some time and have finally decided to tackle a major restoration project on my vintage '77 hi-fi gear.

I'm starting my trial-by-fire with my 2 SPEC-2 power amps, which I use to bi-amp my Infinity QLS-1's. Both of these amps exhibit the same problem... They power-on and work perfectly when they've been off for a few days, but once turned off & back on within the same day they will show a static 10watt+ 'signal' on the power meters and stay in protection mode for a hour or more. During this time the 'signal' slowly dissipates down to 0, at which point they come out of protection mode (with a slight speaker 'thump') and once again proceed to work normally.

EchoWars' excellent posts on refurbing this amplifier indicate that replacing all the TO-220 transistors Q4/Q5/Q6/Q7 and Q12/Q13, along with replacing the problematic reed relay RL1, *should* solve this type of problem? Is this correct?

Forgive me but my background is in digital electronics, not analog, so after replacing the transistors above is the idle current adjustment mandatory?

Assuming the idle current adjustment is required, this is done with a dvm (I use a Fluke 187) with + connected to wire-wrap point 26 and - connected to wire-wrap point 13, then adjusting VR1 to obtain/maintain 30mv over 30 minutes? Correct? Is 25mv preferred over 35mv (i.e.: how much, if any, latitude is allowed)?

Is the current limiter sensitivity adjustment also mandatory? I have a Tektronix TDS380 400MHz scope; a 4ohm 200watt non-inductive load; and the Fluke 187 dvm... But I'm short the signal generator. I'm sure I can borrow one, but am curious as to if the software solutions, like this one - http://www.nch.com.au/tonegen/screenshots.html - would work OK? Further, I understand that a 1000Hz signal is used, but what type of waveform, square/sine/triangle/sawtooth, should I use? The one in the SPEC-2's Service Manual appears to be a highly-clipped triangle waveform -- is that what I'm looking for as I adjust VR2/VR3?

In addition to the precautionary warnings on unmounting the STV-3H/STV-4H temp sensing diode paks are there any other helpful hints or 'gotchas' that I should be aware of?

Since the amps work/sound perfect otherwise, are there any additional items I should check/replace?

Any problems using Deoxit D100L on the trim pots VR1/VR2/VR3, connectors, and main volume pots?

Since I prefer neatness, any problems using silicone (thermal) TO-220 insulators instead of micas-with-messy-heatsink-grease?

Also along the lines of neatness, wouldn't the relay pictured below be a better replacement for the reed relay RL1?

Known needed parts have been ordered, so I'll post pictures as I proceed with the repairs...

Thanks so much for the help!

-Surgeon-

Surgeon said:

Forgive me but my background is in digital electronics, not analog, so after replacing the transistors above is the idle current adjustment mandatory?

Known needed parts have been ordered, so I'll post pictures as I proceed with the repairs...

Thanks so much for the help!

-Surgeon-

Click to expand...

No big rush, since we're in a parts hold here....

Easy stuff first, Re: idle current adjust.... most assuredly YES, when anything is disturbed - better safe than sorry. It's EASY to do, especially on that type of amp (not a "non-switching" amp).

In that vein, a dim bulb tester for the first powerup can save a lot of heartache, and a trial adjustment of the idle current up AND BACK DOWN with the DBT connected the first time will catch any lurking problems that pop up with increased idle current - and remember that the unit ON the DBT is operating at a reduced line voltage , so no permanent adjustments - on full power you can get a nasty surprise doing that - LOTS of Idle current.

The waveform input for the power limiter test is mostly for a steady state signal, where you are trying to hit a particular level. A triangle waveform would show the clipping effect a little more distinctly than a sine imho but I suspect it's a sine wave drawn badly. edit - NO triangle, use SINE - it's a crappy drawing.

If the current limiter is set too low, or malfunctioning, it'll drive you nuts trying to figure out what's happening as you try to adjust idle UP, with it pulling DOWN. Personally my plan for working on that area in any specs (none yet - more's the pity...) that have a problem, is to pull the limiter transistors out, get everything squared away, THEN put them in and deal with them.

edit: as far as I know, EchoWars uses the good silicon type pads.

markthefixer said:

No big rush, since we're in a parts hold here...

Click to expand...

Actually, not so much, as tracking info shows the parts will be delivered on Monday which is why I hoped to get my questions/concerns addressed over the weekend...

And as far as the DBT goes, what wattage would be recommended? (Should I 'go green' and use CFL's? )

-Surgeon-

A 100W lamp is appropriate.

Surgeon said:

Actually, not so much, as tracking info shows the parts will be delivered on Monday which is why I hoped to get my questions/concerns addressed over the weekend...

And as far as the DBT goes, what wattage would be recommended? (Should I 'go green' and use CFL's? ) )

-Surgeon-

Click to expand...

I think you know the answer already......

it's low electronic wattage and all the circuitry inside will probably interact badly, could end up smoking it and the surges as they die could hurt the unit under test. I wouldn't risk it. Not for only 15 watts draw.

You're NOT replacing the trimpots?????????????????????????????

The rest of the answers I defer to EchoWars, or anyone else who has actually dug deeply into the Spec-2

Please, Pretty Please replace the trimpots. It's much smoother when adjudstment time comes. In the case of the current limiter things will be hot and a need to hurry is imperative. No sense fighting a cranky $1.29 pot. The Bourns 3386H-101LF for the 100 ohm and the Bourns3386H-501LF for the 500 ohm.
They're worth the trouble replacing.
Lee

laatsch55 said:

Please, Pretty Please replace the trimpots. It's much smoother when adjudstment time comes. In the case of the current limiter things will be hot and a need to hurry is imperative. No sense fighting a cranky $1.29 pot. The Bourns 3386H-101LF for the 100 ohm and the Bourns3386H-501LF for the 500 ohm.
They're worth the trouble replacing.
Lee

Click to expand...

There you go, the actual numbers, which are rather important as they specify in which direction the adjustment is accessed.. I wasn't sure about the direction....

laatsch55 said:

Please, Pretty Please replace the trimpots. Lee

Click to expand...

Thanks a lot Lee for the part#'s... I've ordered the trimpots and they should be here on Friday. That's exactly the kind of information I'm looking for from anyone who's been-there-done-that on the Spec's...

I got another tip that I shoud also replace the meter lamps while I'm at it so I've ordered replacements for them also.

And thanks to Mark for the DBT recommendation & the test waveform information. Speaking of which, if I am using a 1KHz triangle to adjust the current limiter what exactly am I looking for in terms of 'clipping' -- adjusting VR2 to the point where the peaks of the upper triangles begin to slightly flatten out and then adjusting VR3 to do the same for the lower peaks?

The relays I mentioned/pictured in my 1st post came in and they look like they will make a nice looking replacement for RL1. I also ordered some open-frame Form-1A relays that may be a 'perfect fit' replacement, but I won't know for sure until I rip the old ones out (which *should* be this weekend). They all have 2K-ohm coils, so I assume they sholud be driven properly?

I was also planing on removing/cleaning/reseating all the TO-3 output power transistors. Is this suggested/worthwhile? Are the sockets likely to be brittle?

Any other last minute advice before I plunge into the deep end???

THANKS!
-Surgeon-

Surgeon said:

And thanks to Mark for the DBT recommendation & the test waveform information. Speaking of which, if I am using a 1KHz triangle to adjust the current limiter what exactly am I looking for in terms of 'clipping' -- adjusting VR2 to the point where the peaks of the upper triangles begin to slightly flatten out and then adjusting VR3 to do the same for the lower peaks?

Click to expand...

You absolutely, positively, do NOT use a triangle wave to set the current limit. If Pioneer had wanted you to use something other than a sine wave, they would have made it abundantly clear in the service manual.

Yes...you must remove the power transistors and clean them, as well as the mica pads and the heatsinks. Replace the mica if they don't clean nicely (I use WD-40).

The current limiter adjustment procedure is pretty much like the manual says. What they don't say (and bless EW's heart for saying so) is that the amp will GET WAY HOT WAY FAST. Don't dwaddle, get it adjusted and shut down.
With a 1khz sine wave out of the sig generator, amp pots on full gain get 30 volts on the outputs, adjust VR2 until the limiterts kick in. It's not a subtle thing when it happens you'll KNOW. That's done. That was just the positive part of the waveform, the negative is adjusted through VR3, the only difference being fed 28.3 volts from the generator.
You're not looking for anything exotic, when the limiters kick, leave the pot there, you're done, and again , have your poop in a group and don't screw around getting it done. It's a wee bit intimidating till you do it once, then you'll understand.

The TO-3 sockets for the outputs are high dollar and should not be brittle, I haven't seen any yet. And watch that STV4.

Hey Guys...

Well, it seems that the majority of the parts I ordered have arrived so I'm going to start ripping things apart over the weekend!

I'm not 100% sure that I can fix all the problems, but to help with the diagnosis I ordered a couple of Cat Scans anyway...





-Surgeon-

Looks like the doc's are hard at work.

4 footed Gynechologists

Nice Rack!

Ramundo said:

Nice Rack!

Click to expand...

If you think that's a "nice rack" then you ain't seen nothin' yet... Just wait until I upload a picture of my wife's... :thmbsp:

Just kiddin' of course and I do thank you for the kind comment! It's always been one of my pride & joys considering I went without food/clothing/gas when I was a young pup to purchase it all new from local stereo shops... It was BIG BUCKS back in the day for a married college student working part time for minimum wage!!!

-Surgeon-

I thought I'd eat some bandwidth & upload a little photo essay of my refurbing progress so far...



I expected to find more dust for 30+ years of accumulation, but my bottom amp was generally really clean:






This is the left-side amp (which was the most problematic):






Ouput transistors view of the amp:







NOTE: As per EchoWars, don't forget to remove ALL the output transistors & clean the old grease from them, both sides of their mica insulators, and the main heat sink itself. Then sparingly (trust me -- less is more!) apply a new coat of heat sink compound to both sides of the mica insulators & re-install them.




(CONTINUED NEXT MESSAGE)
-Surgeon-

This is the 24V SPST Reed Relay I used to replace the problematic RL1:




This relay looks really good when installed but it requires the pins to be 'formed' inward & apart slightly to fit the original holes (they need to be where I placed the red dots.) Pins 1 & 2 are the 24V coil and 3 & 4 are the SPST reed switch.

It's available as telco surplus for $1.75 each from: http://www.surplussales.com/Relays/REReed-1.html -- the part# is (KO) R5338-3 .

Once it's soldered in place you'd swear it was an original part (as I'll show in another view below).



(CONTINUED NEXT MESSAGE)
-Surgeon-

Since heat is no-doubt what kills the original TO-220 transistors, I wanted to see if I could possibly install some additional heat sinks to improve the heat dissipation and provide the new replacement transistors with a longer, happier life...

After a long search I came across these TO-220 winged-add-on sinks made by Aavid Thermalloy (Mfg Part# 507102B00000G) -- available from Allied Electronics for $0.27 each here: http://www.alliedelec.com/search/productdetail.aspx?SKU=6195071

In order to install them on the 4 individual TO-220 transistors, I chose to modify the original Pioneer heat sinks by grinding off the protruding part of their built-in threaded screw mount (see 1st photo below). I then applied a little heat sink compound between the two heat sinks & assembled them together as shown in the 2nd photo... In order to affix the new transistors you must now use a standard TO-220 fine-threaded mounting nut as shown in the "Assembled" photo below.

I also used the same add-on heat sinks mounted to the outside of the TO-220 tabs (their original design) for the double-mounted transistors. (With some slight 'forming' of their fins to clear nearby components.)

I believe that by increasing the size of the heat dissipation area the transistors can't help but run a little cooler, and a cooler transistor lives a longer life!!!



TO-220 Heat Sink modification to add additional heat-disipating area:






Assembled TO-220 transistors ready to be re-installed:






(CONTINUED NEXT MESSAGE)
-Surgeon-

All parts have been soldered in & ready to close:






Side view of the completed repair job:






(CONTINUED NEXT MESSAGE)
-Surgeon-

Close-up view of the new Reed Relay replacement for RL1:






ALL THE NEW GOODIES CAN BE SEEN HERE:






OK... So all I have to do is lather/rinse/repeat the above process 3 more times (because I have 2 amps) and then it's time to plug 'em in and see if we can get the trimpots adjusted to the correct levels...


Hopefully WITHOUT releasing any of that MAGIC BLUE SMOKE...



-Surgeon-