Hi! ok R64 is a 220 ω resistor & Q22 is a BD140 transistor, these 2 components are the final outputs for the -15V rail which feeds the pre-amp board. There are two scenarios here, firstly Q22 may have died of natural causes which has killed R64 or something has gone short on the pre-amp board which has taken both components out as a result. i would suggest replacing the two cooked components & if the amp then works ok it will be an easy repair, however if they go again then an investigation using an ohm meter will be needed on the pre-amp board to check for shorts on all any of the i.c's. let me know how you get on, if I can be of further assistance just ask!. Regards, acbva.
Hello again after posting the above solution I seemed to remember that this was a common problem on these amps, as it is a few years since I have repaired one I took out the circuit diagram again & came across a modification to the circuitry I designed to overcome this problem. Basically the components involved originally are underrated - this mod has to be carried out on both sets of components with regards to the + and - 15V rails so here we go. Replace R61 & R64 with 220 ohm / 3 Watt wirewound resistors. Replace Q23 with a TIP31C / Q22 with a TIP32C. Now the hard bit! I found that this mod lasted longer but found the amps were coming back in the summer after hot days with the same fault, therefore a re-think was needed. the only way I found to overcome this was to mount the two transistors on the reverse side of the PCB (print side) & fit silica pads to the back of each transistor & when the amp is re-assembled the transistors use the base of the amplifier to dissipate their heat - this is the only long term cure. If you need more details just ask please. Regards, acbvaHello again after posting the above solution I seemed to remember that this was a common problem on these amps, as it is a few years since I have repaired one I took out the circuit diagram again & came across a modification to the circuitry I designed to overcome this problem. Basically the components involved originally are underrated - this mod has to be carried out on both sets of components with regards to the + and - 15V rails so here we go. Replace R61 & R64 with 220 ohm / 3 Watt wirewound resistors. Replace Q23 with a TIP31C / Q22 with a TIP32C. Now the hard bit! I found that this mod lasted longer but found the amps were coming back in the summer after hot days with the same fault, therefore a re-think was needed. the only way I found to overcome this was to mount the two transistors on the reverse side of the PCB (print side) & fit silica pads to the back of each transistor & when the amp is re-assembled the transistors use the base of the amplifier to dissipate their heat - this is the only long term cure. If you need more details just ask please. Regards, acbva
Hello again, seems odd that the component numbers I supplied do not tally up to what you have on your PCB, I no longer have any 800.2's lying around to have a look either I am just going by my original kicker circuit diagrams. from what I remember there was no bias towards any one channel going faulty so I decided to just modify both. It certainly looks like the mod has been done as the original transitors (BD139/140) were mounted vertically on the pcb alongside all of the other components & relied on the air-flow drawn in by the fan for cooling purposes. As these were passing too much current in this circuit they naturally overheated until one or the other went short circuit. One thing I omitted to mention is that a heat-resistant rubber pad must be placed between the PCB & the transistor body to "push" the transistor onto the base of the amp for maximum heat dissipation, if this is not in place then the transistor will not sit completely flat & will cause hot spots & eventual destruction. You seem to have different ref. numbers for the resistors in question. The two concerned are each connected to the collector of both transistors & are as mentioned 220 ohm & must be rated at 3 Watts, not the one Watt jobs that came as standard, if memory serves me correct. If you like I can scan & send you the circuit diagram for the area in question if you like, just supply me you email address. If you find you do not have the rubber pads in place let me know & I can pop a couple in the post for you (Presuming you are in the UK!) Is the remaining working transistor a TIP31/32 as mentioned in the mod? All the best. acbva.Hello again, seems odd that the component numbers I supplied do not tally up to what you have on your PCB, I no longer have any 800.2's lying around to have a look either I am just going by my original kicker circuit diagrams. from what I remember there was no bias towards any one channel going faulty so I decided to just modify both. It certainly looks like the mod has been done as the original transitors (BD139/140) were mounted vertically on the pcb alongside all of the other components & relied on the air-flow drawn in by the fan for cooling purposes. As these were passing too much current in this circuit they naturally overheated until one or the other went short circuit. One thing I omitted to mention is that a heat-resistant rubber pad must be placed between the PCB & the transistor body to "push" the transistor onto the base of the amp for maximum heat dissipation, if this is not in place then the transistor will not sit completely flat & will cause hot spots & eventual destruction. You seem to have different ref. numbers for the resistors in question. The two concerned are each connected to the collector of both transistors & are as mentioned 220 ohm & must be rated at 3 Watts, not the one Watt jobs that came as standard, if memory serves me correct. If you like I can scan & send you the circuit diagram for the area in question if you like, just supply me you email address. If you find you do not have the rubber pads in place let me know & I can pop a couple in the post for you (Presuming you are in the UK!) Is the remaining working transistor a TIP31/32 as mentioned in the mod? All the best. acbva.
Answers & Comments
Hi! ok R64 is a 220 ω resistor & Q22 is a BD140 transistor, these 2 components are the final outputs for the -15V rail which feeds the pre-amp board. There are two scenarios here, firstly Q22 may have died of natural causes which has killed R64 or something has gone short on the pre-amp board which has taken both components out as a result. i would suggest replacing the two cooked components & if the amp then works ok it will be an easy repair, however if they go again then an investigation using an ohm meter will be needed on the pre-amp board to check for shorts on all any of the i.c's. let me know how you get on, if I can be of further assistance just ask!. Regards, acbva.
Hello again after posting the above solution I seemed to remember that this was a common problem on these amps, as it is a few years since I have repaired one I took out the circuit diagram again & came across a modification to the circuitry I designed to overcome this problem. Basically the components involved originally are underrated - this mod has to be carried out on both sets of components with regards to the + and - 15V rails so here we go.
Replace R61 & R64 with 220 ohm / 3 Watt wirewound resistors.
Replace Q23 with a TIP31C / Q22 with a TIP32C. Now the hard bit!
I found that this mod lasted longer but found the amps were coming back in the summer after hot days with the same fault, therefore a re-think was needed. the only way I found to overcome this was to mount the two transistors on the reverse side of the PCB (print side) & fit silica pads to the back of each transistor & when the amp is re-assembled the transistors use the base of the amplifier to dissipate their heat - this is the only long term cure.
If you need more details just ask please. Regards, acbva
Hello again, seems odd that the component numbers I supplied do not tally up to what you have on your PCB, I no longer have any 800.2's lying around to have a look either I am just going by my original kicker circuit diagrams. from what I remember there was no bias towards any one channel going faulty so I decided to just modify both. It certainly looks like the mod has been done as the original transitors (BD139/140) were mounted vertically on the pcb alongside all of the other components & relied on the air-flow drawn in by the fan for cooling purposes. As these were passing too much current in this circuit they naturally overheated until one or the other went short circuit. One thing I omitted to mention is that a heat-resistant rubber pad must be placed between the PCB & the transistor body to "push" the transistor onto the base of the amp for maximum heat dissipation, if this is not in place then the transistor will not sit completely flat & will cause hot spots & eventual destruction. You seem to have different ref. numbers for the resistors in question. The two concerned are each connected to the collector of both transistors & are as mentioned 220 ohm & must be rated at 3 Watts, not the one Watt jobs that came as standard, if memory serves me correct. If you like I can scan & send you the circuit diagram for the area in question if you like, just supply me you email address. If you find you do not have the rubber pads in place let me know & I can pop a couple in the post for you (Presuming you are in the UK!) Is the remaining working transistor a TIP31/32 as mentioned in the mod? All the best. acbva.