Pioneer SPEC 2 restoration help
- Thread starter slipstream55
- Start date
slipstream55
Active Member
Stupid question time (please have mercy on me)...the SM doesn't indicate which pin the + meter probe is supposed to be connected to. Since the scanned SM is b/w, I'm only seeing a black or white lead going to unmarked meter inputs. I'm checking idle current now and have 25 minutes to go for warm-up. My black probe is on pin 26 and red probe is on pin 13, pin-wise, the same pins as in the SM. I'm getting -3.7mV on the RH amp board but it isn't warmed up yet. I'm waiting...thanks, anyone.
Mark
Mark
When measuring offset voltage at the amplifier output, the sign ( + or - ) of the voltage isn't as important as it's magnitude, and it's difference from the ideal reading of zero.
When measuring bias current of the power output transistors across emitter resistors, the sign of the voltage will always be constant, as curent flows in a specific direction between the positive supply and the negative supply. Thus if you have an analog meter, you would know immediately to reverse the leads, because the needle would swing below zero, where it cannot be accurately read. With a modern DMM, that is not as important, as most meters will automatically compensate for the negative voltage. You could as a matter of good form, reverse the leads if the reading is a negative voltage. See if there is any change to the magnitude of the reading after the lead reversal. There shouldn't be...
When measuring bias current of the power output transistors across emitter resistors, the sign of the voltage will always be constant, as curent flows in a specific direction between the positive supply and the negative supply. Thus if you have an analog meter, you would know immediately to reverse the leads, because the needle would swing below zero, where it cannot be accurately read. With a modern DMM, that is not as important, as most meters will automatically compensate for the negative voltage. You could as a matter of good form, reverse the leads if the reading is a negative voltage. See if there is any change to the magnitude of the reading after the lead reversal. There shouldn't be...
slipstream55
Active Member
Hi, markthefixer. Based on your response, if the lead polarity doesn't matter, could I not adjust VR1 for +30mV as well as -30mV based on the direction VR1 is turned (cw v.s. ccw)? Which voltage reading would be right? Thx.
Mark
Mark
slipstream55
Active Member
I swapped leads (Fluke 8024B). The absolute value didn't change but the sign (+/-) did. Red is now on pin 26, black on pin 13. Idle current is reading 6.3mV. Tried adjusting VR1 cw and got as far as 17.6mV and stopped as this was a pretty good turn on VR1. How much play (# of turns) does this adjustment have? I'm thinking not very much.
Mark
Mark
slipstream55
Active Member
As it stands now, RH channel will only adjust up to about 17mV and LH channel does not adjust at all. I returned both adjustments to where they were originally, physically. Idle Current values are: RH (6.3mV), LH (65.7mV).
ity:
ity:
No bias? Re-read post #8.
And I'll reiterate that the bias current on the Spec 2 is very dependant on the temperature of the pre-drivers, drivers, and output transistors. It can start out at a very low value, and climb over a period of an hour or more till it reaches its stable point.
And I'll reiterate that the bias current on the Spec 2 is very dependant on the temperature of the pre-drivers, drivers, and output transistors. It can start out at a very low value, and climb over a period of an hour or more till it reaches its stable point.
slipstream55
Active Member
Thanks, EW. Actually, I was reading those very threads this afternoon. I didn't expect I was going to have to use the information, though. I guess this SPEC isn't in as good a shape as I was hoping. DRAT! :tears::tears::tears:As it stands now, RH channel will only adjust up to about 17mV and LH channel does not adjust at all. I returned both adjustments to where they were originally, physically. Idle Current values are: RH (6.3mV), LH (65.7mV).
The SPEC 2 was sitting powered "on" for over an hour when I took the readings so it should have been fairly stable. Those Idle Current pots are 1-turn pots, aren't they? :yes:
Anyway, I had been monitoring the meter and the values hadn't changed for the last 15 minutes past the 1 hour warm-up.Oh, well. Now I get to take it apart. It's pretty dirty anyway. I hope to take pix tomorrow. If I do, I'll post some. Thx.
slipstream55
Active Member
I've gotten around to taking some pictures of my SPEC 2 and I think I want to take back my previous comment about the amp NOT being in too bad a shape. "Rough" really doesn't quite describe it. I am surprised it worked as well as it did. Now I have to decide whether this is a candidate for restoration or for parts. :yes: I am including 5 of the "worst of the worst" pictures of the SPECs condition. Comments are welcome. :thmbsp: :thumbsdn: I'll post some more pix later.
Enjoy
I am including 5 of the "worst of the worst" pictures of the SPECs condition. Comments are welcome. :thmbsp: :thumbsdn: I'll post some more pix later.Enjoy
slipstream55
Active Member
Well, later came sooner. Here's 5 more pix of my SPEC 2. Some of the components don't look too bad as seen in the pictures. Some of the other ones, well.....
Again, comments welcome. Is this a candidate for a miracle or what?
Enjoy (or not).
Again, comments welcome. Is this a candidate for a miracle or what?
Enjoy (or not).
slipstream55
Active Member
EchoWars. I saw in some other threads regarding SPEC 2 restorations you have done for other AK members that you have a DC Offset adjustment circuit you have installed in said SPEC 2s. Is this circuit mod privy only to you or is it available to other DIY AK members? If available, can I get it from you? Regarding my SPEC restoration...I'm already pricing out a deep sea diving suit. I think I would like to acquire a second SPEC 2 in good physical condition but non-working and combine parts from both to make a good working as well as showable unit. Might be cheaper this way. Thanks.
slipstream55
Active Member
Thank you for the thread link on the DC Offset, EW. :ntwrthy:
BTW, I have removed both PA modules from my SPEC 2. I am posting pictures I took of each module. Pictures of the RH module are in this post. When you compare the pictures of the LH module I will be posting next, you'll notice some differences in the thermal sensors as well as the relays. My gut feeling is that the LH module has more original parts than the RH module and that the RH module is pretty much a hack job done by someone. :bash: Any comments?
I wanted to remove the P/S board for inspection and cleaning but it doesn't look like it is easily removed due to the wire density and no disconnects. Damn. (Though I'm thinking it wouldn't hurt to replace some of the wiring while it's apart, at least the worst of the wires...I can wire-wrap).
The big caps and transformer look great. At least that's something. Anyway, here's some pix.
BTW, I have removed both PA modules from my SPEC 2. I am posting pictures I took of each module. Pictures of the RH module are in this post. When you compare the pictures of the LH module I will be posting next, you'll notice some differences in the thermal sensors as well as the relays. My gut feeling is that the LH module has more original parts than the RH module and that the RH module is pretty much a hack job done by someone. :bash: Any comments?
I wanted to remove the P/S board for inspection and cleaning but it doesn't look like it is easily removed due to the wire density and no disconnects. Damn. (Though I'm thinking it wouldn't hurt to replace some of the wiring while it's apart, at least the worst of the wires...I can wire-wrap).
The big caps and transformer look great. At least that's something. Anyway, here's some pix.
slipstream55
Active Member
Here are pictures of the LH PA module. Some of the board components on both modules are showing signs of tarnish, rust or corrosion. Is there anything that I can use to clean them up a bit or should they be replaced?
slipstream55
Active Member
cbrworm:
I have no idea. That's the way it was when I bought it. If I'd had any idea what condition things were in under the hood, I might have had second thoughts about buying it in the first place.ity: What hooked me on it was simply finding a SPEC 2 in working condition in a pawn shop (or any store for that matter) for $200. I passed it up the first time I saw it and after a week of fighting with myself about whether to buy or not, I went back for it. Buy then the owner had raised the price and gave me a load of crap about not buying it the first time I saw it. 
I should have walked but didn't (oh, the lure of those Pioneer SPEC 2 amps). As it was, I talked him back down to $200 but had to eat crow in the process. I hate crow.:yuck:
I have no idea. That's the way it was when I bought it. If I'd had any idea what condition things were in under the hood, I might have had second thoughts about buying it in the first place.
ity: What hooked me on it was simply finding a SPEC 2 in working condition in a pawn shop (or any store for that matter) for $200. I passed it up the first time I saw it and after a week of fighting with myself about whether to buy or not, I went back for it. Buy then the owner had raised the price and gave me a load of crap about not buying it the first time I saw it. I should have walked but didn't (oh, the lure of those Pioneer SPEC 2 amps). As it was, I talked him back down to $200 but had to eat crow in the process. I hate crow.:yuck:I would have grabbed it too. I would still grab it.
It's just interesting to me that someone managed to replace the impossible to find diode packs with what looks like 3 diodes in a series (wrapped in electrical tape) and managed to (hopefully) get the bias current to track properly. As silly as it sounds, that is my biggest fear in these is breaking the diode pack during maintenance. AFAIK everything else can be replaced (at least on my SX)
It's just interesting to me that someone managed to replace the impossible to find diode packs with what looks like 3 diodes in a series (wrapped in electrical tape) and managed to (hopefully) get the bias current to track properly. As silly as it sounds, that is my biggest fear in these is breaking the diode pack during maintenance. AFAIK everything else can be replaced (at least on my SX)
There are two diodes remote-mounted on the heatsink on each driver board...one is a STV-3H, which is a pain to get but not impossible, and I have a few spares for use on gear that I work on. The other is a STV-4H, and I know of NO source for these except out of old gear. I think I have one device stashed away somewhere, and since many of my own personal units have one or two of these devices, I'm saving it for a rainy day.
The one STV-4H that I bought, I found on eBay a while back.
The one STV-4H that I bought, I found on eBay a while back.
