For Pioneer SA-9100 Integrated Amps with Intermittent Protection Faults

[pustelniakr]

This is not a complete restoration of this model, but only addresses a common problem with these units at this age. Truth be told, I consider this model to be one of the sweetest sounding amps that have passed over my restoration bench. If I may go out on a limb, it is pretty much from just this side of the tube era, and does satisfy the tube attuned ear quite nicely.

I should have never begun to sing the praises of this model. Since I started, prices really began to shoot up. If you are lucky enough to come across one you can obtain, I fervently recommend it.

What follows will be the most frequent causes for intermittent protection faults for this model.

 

[pustelniakr]

The 2 390 ohm, 1/2 watt resistors on the power supply B (regulator) board are just a bit under-sized and tend to fracture and crack, becoming intermittent. Replace with 1W, metal oxide resistors. they will fit in the original space, and add a bit of de-rating, which is greatly needed.

The big hitter for this kind of problem is Q1, which is a 2SD313. The heatsink is undersized for this part, and eventually you will get the transistor encapsulation to crack, exposing it's innards to the air. There is where most of you will find the source of intermittent protection faults. Frequently, when the transistor is on its way out, it will become vibration sensitive. Light taps on its heatsink will cause protection faults of various lengths.

2SD313 transistors are still available, if you look.

For SA-9100s, in addition to recapping and refreshing all circuit board solder joints, as well as DeOxiting user controls, the following should be done, as a matter of course:

• Lightly burnish the protection relay contacts
• Replace protection relay driver, Q7, on the protection board (2SC1384, still available from Digikey as ROHS part: 2SC13840. This one is likely stressed by overvoltage, due to flyback voltage from relay coil upon release.)
• Replace Q6 on the protection board (2SC945, use ZTX-694B from Digikey...relay coil voltages again)
• Replace Q5 on the protection board (2SA733, use ZTX795A from Digikey...relay coil voltages again)
• Add 1N4004 across the protection relay coil, cathode to the high (+), to snub flyback votages when relay is released)
• Replace Q1 on Power Supply Circuit-B board (2SD313, available from Newark/MCM, heatsink is undersized and this one is either bad, or going bad)
• Replace Q2 on the Power Supply Circuit-B board (2SB507, available from Newark/MCM also likely to be thermally stressed, but not as bad as Q1)
• Replace resistors, R12 & R13, as stated above.

Of all the parts to replace, I suggest that the main hitters for intermittent SA-9100 protect faults are (in order of priority): Q1 on the power supply board, and Q7 on the protection board. Also, I would expect Q5 on the protection board to go before Q6, as supplemental places to suspect.

Please, replace all 'lytic caps on the power supply circuit-B board. Particularly the ones anywhere near the heatsinks and hot transistors. Use 105 degC parts instead of the standard 85 degC parts.

Enjoy,
Rich P

 

[pustelniakr]

Supplemental:

If your amp operates without intermittent protection faults, as received, I suppose you could enjoy it for a while, but watch it carefully. If such faults occur, do at least this:

Lightly burnish the protection relay contacts

Replace protection relay driver, Q7, on the protection board (2SC1384, still available from Digikey as ROHS part: 2SC13840. This one is likely stressed by overvoltage, due to flyback voltage from relay coil upon release.)

Replace Q6 on the protection board (2SC945, use ZTX-694B from Digikey...relay coil voltages again)

Replace Q5 on the protection board (2SA733, use ZTX795A from Digikey...relay coil voltages again)

Add 1N4004 across the protection relay coil, cathode to the high (+), to snub flyback votages when relay is released)

Replace Q1 on Power Supply Circuit-B board (2SD313, available from Newark/MCM, heatsink is undersized and this one is either bad, or going bad)

Replace Q2 on the Power Supply Circuit-B board (2SB507, available from Newark/MCM also likely to be thermally stressed, but not as bad as Q1)

Replace resistors, R12 & R13, as stated above.

Of all the parts to replace, I suggest that the main hitters for intermittent SA-9100 protect faults are (in order of priority): Q1 on the power supply board, and Q7 on the protection board. Also, I would expect Q5 on the protection board to go before Q6, as supplemental places to suspect.

Please, replace all 'lytic caps on the power supply circuit-B board. Particularly the ones anywhere near the heatsinks and hot transistors. Use 105 degC parts instead of the standard 85 degC parts.

Enjoy,
Rich P