spec2 pioneer power amp

[lateretroguy]

I have a spec2 pioneer that I was listening to records one day and the protection light came on both meters buried.I have checked all the transistors they are good I have also checked all the caps which hadn't been too long since they were replaced and so were the transistors.

 

[zebulon1]

Check the center speaker terminals at the amp boards for DC voltage. The terminals are Found at the top of the boards. See the scat for the proper pins. Edit: Pin 20 of the amp boards AWH-045.
Both channels is rare. Points to a power supply.
Check fuses 3 and 4 of the Power supply assembly AWR-093.

 

[lateretroguy]

Check the center speaker terminals at the amp boards for DC voltage. The terminals are Found at the top of the boards. See the scat for the proper pins. Edit: Pin 20 of the amp boards AWH-045.
Both channels is rare. Points to a power supply.
Check fuses 3 and 4 of the Power supply assembly AWR-093.

I found a blown fuse between the 2 protection relays I replaced it with the same size and it has not blown but still will not come out of protection mode on the left channel I have 458 mv and on the right channel I have 36.7 mv

 

[zebulon1]

You took the readings at the amp boards? Very good.
The 458mV's is high.
Probably shouldn't power it on until you can shore up that amp. Some resistance entered the circuit. Not a good sign.
Not that well known but I've seen a few:
The TO-220 drivers can get hot enough to desolder them self's.
It's going to need a freshening up.

 

[lateretroguy]

I checked the transistors and caps in the meter board and they checked good but I freshed it up again now the meters are both down when I switch it on but the lights flicker once and nothing else happens.I checked my pinout on the transistors and they show to be correct A992 pnp and a c1845 npn, mje15033g pnp, c2690a-y npn.

 

[ivandezande]

I checked the transistors and caps in the meter board and they checked good but I freshed it up again now the meters are both down when I switch it on but the lights flicker once and nothing else happens.I checked my pinout on the transistors and they show to be correct A992 pnp and a c1845 npn, mje15033g pnp, c2690a-y npn.

You need to do a lot more testing on the unit looking for bad parts, get some readings, and build a DBT.

 

[lateretroguy]

What is a dbt?

 

[lateretroguy]

I did check the power transistors in the amp boards and I had a couple blown I also had 2 733 and 2 c945 so I replaced them now the meters only go up to the 1 now

 

[lateretroguy]

I also checked the rest of the transistors and caps and they show to be good so I put them back in.On the diode setting on my meter they show 6.7 one way and nothing the other direction

 

[zebulon1]

DBT = Dim Bulb Tester
You use it before applying full line house power. It will limit the current and indicate a short in the amp and most of the time, save expensive components. It's always a good idea to use it after any work on the amp.
If the bulb remains bright a short exists and must be corrected before line power is applied.

 

[lateretroguy]

Now I know what you mean I have one when I apply current to the unit it starts out bright and goes out and the unit says illuminated but the protection light stays on and the meters go up real slow about a 1/4 of the way. I figured it would be a blown transistor so I checked them and I found several blown power transistors.I have a few spare so I put them in but I still have the same issue,it is better but not fixed

 

[ivandezande]

Now I know what you mean I have one when I apply current to the unit it starts out bright and goes out and the unit says illuminated but the protection light stays on and the meters go up real slow about a 1/4 of the way. I figured it would be a blown transistor so I checked them and I found several blown power transistors.I have a few spare so I put them in but I still have the same issue,it is better but not fixed

At this point check all transistors everywhere for shorts and be sure you're putting them in the correct way, sounds like the amp is really messed up.

 

[lateretroguy]

After I found some blown to3 transistors in the both channels of the amp boards and replaced one fuse the meters are now down all the way when you power it up but the protection light stays on?

 

[lateretroguy]

All fuses are good

 

[ivandezande]

All fuses are good

....did you adjust the offset? Is it biasing?

 

[lateretroguy]

How do I check that?

 

[ivandezande]

How do I check that?

I take it you've haven't bothered to read the service manual or read any other threads on the repair of a Spec 2.
Please do those things, this is a pretty big, expensive amp you're working on and for your safety and for the hope of getting it working again you should know a lot about what your dealing with.

 

[zebulon1]

 

[lateretroguy]

I looked once many I overlooked it I will look again.

 

[lateretroguy]

I looked once that was a typo sorry.