Pioneer SX 2500 (No AM/FM)

[cbertrand]

Hi all, I recently picked up a Pioneer SX 2500 to use as a phono preamp. I took it apart and cleaned everything and it is working well as a preamp. The speaker outputs also work when it is switched in to amp mode.

However, I get no sound for AM or FM, no fuzz, nothing. I imagine that power is not making it there but I need someone to point me in the right direction to start troubleshooting. I am not experienced (yet) in component level electronic repair so please talk slow

So far in my new hobby I have gotten a Technics SL-1900 pluged into this Pioneer SX 2500 as a preamp and that is going into my Denon reciever for my surround sound. So far, so fun! I would love to fix the tuner, then I would feel justified buying the bulbs/leds to fix all the missing lights.

 

[Punker X]

Usually there is a separate power supply for the tuner sections. 12 ish volts. Find the manual and start investigating. Could be a fuse. No time this morning to look over the manual myself.

 

[cbertrand]

I will pull it apart tomorrow, I already have the manual I am just worried I will fry something. Is there a good tutorial you would recomend on tracing the power flow? I have a good multi meter. Also what is the best way to ID the incoming power to a given board? Sorry for the n00b questions

 

[Punker X]

Should have asked if there is any meter movement at all. Do the tuning or signal meter move when trying to tune in a station. Assumed they were dead. If they are probable power supply.

If you have clips attach leads with the power off. Many a unit has been made worse by errant probes. I would start by measuring the output of the power supply. You would be mainly concerned with B3 and 4.. 12 and 13 volts. If there. Then you may have to check each section and check for voltage in the circuit. If the voltage is no there, then check the resistors and transistors in the power supply.

 

[cbertrand]

No, no movement on the meter or signal when I attempt to tune. Where is the best place to connect the ground/common?

 

[cbertrand]

Okay, I found the E terminal and grounded to that.

B3 = 0.72 volts
B4 = 12.58 volts

Seems like B3 is the problem circuit. What is my next step?

 

[cbertrand]

Okay, I tried testing the transistors and resistors in circuit but that is not working. I am a bit intimidated with the number of wires coming off of this board. I don't have access to both sides of the board without taking it off. Any tips on how to properly unwind and mark all the wires on the board so I can get it back together properly? If I take this thing off I suppose I will also try to recap it while I am at it.

A few questions:

1. Should I take it off and try to then take to transistors out of circuit to test them properly?
2. Should I just buy a variable DC power supply and hot wire the terminal to see if the radio will even work after I do all this? If so how many amps should I put to the B3 terminal?
3. Should I just buy a cheap 12v dc power supply and permanently hotwire it? (Not take the board off) If so how many amps should I put to the B3 terminal?
4. Where should I buy components?

I appreciate all the help.

 

[Punker X]

Wire wrap can be a bitch to work with, they sell an unwrapping and wrapping tool, but even after years I still mess it up trying to undo and redo them. Most of the time you can disconnect the board however it is mounted. Screws or plastic standoff. Take the wires out of any clips and cut the banding or wrapping. Most the time it can be twisted to get to the back of the board. It may require a wire or two be disconnected. You can try to loosen the wrap with needle-nose pliers and slip them off the post. If it just a few, I would probably recommend cutting the wire and re-solder the break and cover with shrink wrap.

So not having at B3 there is a limited number of things that could cause this.

Measure R2 and R4, both sound be low 10 and 33 ohms. If good then measure the anode of of D1 or base of Q1. Should be 13v. If the resistors are good it is either Q1 or D1. If the resistors are open it could be a short condition with Q1 and blew the resistor.

While you have access to the back of the board I would recommend replacing all the electrolytic caps and check all the solder joints.

Good luck..

 

[39cross]

You already have good advice on what to do, but out of curiosity I took a look as well and have a complementary thought. Here is a snippet from the schematic. What do you measure at B1? If B1 reads low, that may directly implicate double diode D1 as bad. The schematic shows two diodes, but these are in a package. It's possible I guess that one may be bad and one good, but if D1 is bad, you can make a replacement using two 1n4007's. See the link: sx-828

 

[cbertrand]

Hey Guys, Thanks for all the help, I will check B1's power output when I get home this evening. In the mean time I was wondering if you folks would mind looking over my shopping list for equivilant components? I figured I would just order everything that could be bad. That a way once I get the board off I will have what I need to move forward. Being new to all of this I made my best attempt to find modern components that have the same values as the oldies but I would like some more experienced eyes on the list before I solder these things on my precious receiver

 

[39cross]

I would recommend using Nichicon PW capacitors in the power supply. You can go slightly up in voltage if needed, but keep the capacitance values the same (i.e. 100uf stays 100uf). Also, the 1n4007's are cheaper by the 10, so why not buy some extras.

 

[cbertrand]

Just ordered the parts, i appreciate the help. Ill post back my results once I am done!

BTW, I had a 12 volt wall adapter lying around and I hardwired that to B3. FM radio came on! So at least I know once I fix the supply things should work! Next step after that is to change the lamps! I already re-oiled the walnut cabinet and it looks great!