So...I have a Marshall VS100R combo on the bench. Blown transistors, and also a bad J111 (T16) and a bad TIP29CH (T4). I already have the output transistors TIP 142 and 147s. Do these equivalent transistors need the mica spacer? I couldn't find the info from the datasheet.
If you mean the insulator between the transistor and heatsink then I would say yes.
Short answer: It depends.
Some transistors have the collector tab totally encapsulated in plastic.
These do not need a mica insulator.
Just heat grease.
If the collector tab is metal then, yes, it must be isolated from the heatsink IF the circuit calls for it.
Some amplifier topologies use a grounded collector.
Well the original transistors were BDV65 and BDV64 and there was no spacers. However the amp was worked on by a previous tech and he deemed it non-repairable, which of course is not the case. TIP 142 and TIP 147 are suitable replacements, I'm just confused as to if that spacer was there previously or if now with the transistor sub it may be required. I'll check the schematic to see if I can tell if the collector was originally grounded.
According to the schematic not grounded. I'll order the spacers.
Not to beat a dead horse but if the TIP 142/ 147 transistors are plastic enclosed at the collector then you do not need the mica. Just grease.
As a matter of fact, it may hinder the transfer of the heat.
It would be nice if you would indicate what you have as both the BDV & the TIP transistors come both ways.
The metal tab type has not been made for over 10 years, if you found some they are old stock or possibly fake.
Like Jazz said, you don't need the spacers for the plastic backed type.
Attached datasheet shows both types.
*EDIT TO-247 package does not have the back insulated and requires insulator.
If you do happen to have found some old style metal tab types, you not only need the mica spacers, but also special plastic washers for the screws.
It originally had transistors with the metal tab. Only held to the heat sink with a surface clamp. The replacements I have are the newer type.
If they are fully encapsulated in plastic then you just need some thermal grease.
A thin layer of grease and try to move the transistor around a bit against the heatsink to spread the grease evenly, clamp it and solder in.
Just poke the legs through the PCB enough to solder them in, it keeps the transistors more towards the center of the heatsink.
There is some metal exposed on the back of these newer transistors. I think it will be best to use the insulators.
Quote from: markorock37 on March 04, 2024, 01:18:36 PMThere is some metal exposed on the back of these newer transistors. I think it will be best to use the insulators.
Thanks for the update. Yes, you need the insulators. I was mistaken as far as the datasheet goes. I found pictures of other transistors with the same package (TO-247) and they are not insulated on the back either.
I replaced the output transistors (TIP 142, TIP 147) and installed with the micas. Also replaced TIP29C and a J111 that were bad. Im getting a low brightness (not really dim) on my bulb limiter and a buzz/hum through the speaker. No guitar signal coming through. Tested for DC at the output jack and it was at 33V! Shut it down and started testing components. All diodes test good, and all capacitors test good. Checked some resistors in areas i felt were critical and haven't found anything off. Do you think one of the TO92 transistors is at fault? Or did I blow an output again?
Looks like I'll have to wait until tomorrow to start testing this entire board.
What is the wattage of your bulb?
I doubt that the 33VDC at the output was when speaker connected as that would be over 130 watts and your speaker would surely be toast.
Never try to power anything up on a limiter bulb while a load is connected to the amp.
Power up with no load. Then, if no DC is present on the output, connect load while unit turned on.
Many amps will not power up properly on a bulb with a load connected.
100W bulb. DC was present with no load.
Check that T7 and T8 and their diodes are ok. Check all 4 of the 0R33 5W resistors.
Power up on the bulb with no load connected.
Measure DC volts at e,b,c, of T4, T6, T9, T12.
All diodes and .33 emitter resistors test good.
T4 E -35.7v
B -35.3v
C 31.5v
T6 E 31.6v
B 31.9v
C 32.1v
T9 E 30.9v
B 32.2v
C 32.1v
T12 E 30.9v
B 31.8v
C 30.8v
The collector on T12 should not be +30.8v, it is connected to the negative rail.
Are you keeping the common (Black) lead of your meter on 0V (ground) all the time ?
It is very important to clearly indicate the positive and negative readings so the experts (not me) can work out what is wrong.
Maybe worth re-measuring the voltages ?
Assuming that the T12 collector voltage TV mentioned is just a typo, T4 voltages do not seem right. E-B voltage indicates it should be turned on, but collector voltage is not pulling down.
T12 E 30.8
B 33.8
C -38.3
So I did have the collector wrong of T12.
Remeasured T4 and voltages listed are correct. Originally had a TIP29CH replaced with TIP29C.
The T4 voltages indicate either T3 is bad and not letting T4 turn on fully, T4 is bad, or something is wrong elsewhere in it's string (shown in red).
bias.jpg
That helps, will report back with my findings..
Everything in that string is good. Retested T4 and T3 are good. Replaced T6. Made sure pinouts are all correct. Still showing voltage at the output.
Can you post E,B,C voltages for TR4 and TR6 ?
Had a few other projects to tend to, but finally got around to getting those voltages.
T6 MJF122
E 34.6V
B 35.5v
C 35.1v
T4 TIP29
E -39.5v
B -39.2v
C 35.2v
Do you have those reversed or is it a typo? T4 should be the TIP29.
I corrected that above, yes it was just a typo. Voltages are correct for the given transistors.
The E to B voltage of T4 (0.3V) seems to not be enough to turn it on. Maybe checking directly with probes at E and B will give a more accurate reading than checking voltage to ground.
The voltage to turn it on should be developed across R5. That is created because of current through T1. What are E,B,C voltages for T1 and T2 ?
T4 E to B 0.3V
T1 E 0.6v
B 0v
C -35.8v
T2 E 0.6V
B 15.1v
C -36.5v
R5 671 ohms
D1 checks good
So looks like T1 is bad?
Yes it would seem T1 is bad as you verified R5 and D1. But you also need to check their solder connections.
As T1 and T2 form a differential amplifier, it is best to replace them as a pair.
I don't see 2SA872 on Mouser, is KSA992 a good sub?
Quote from: markorock37 on April 13, 2024, 02:57:58 PMI don't see 2SA872 on Mouser, is KSA992 a good sub?
Yes, those should work.
Well, I've replaced T1 and T2 as well as D1. Still reading pretty much the same voltages. At this point, all transistors have been replaced in the amplifier portion. I hate to deem this unit a loss but I am leaning that way as it was quite a mess with the traces from prior techs. Im 99% sure I have all the traces repaired correctly.
Hang in there bud 8)
Don't give up before the miracle :P
If anybody can get your amp running these guys can.
Maybe post up some pics of the boards
:)
Yes, pictures should help. Especially of any trace repairs that have been done.
Also, e,b,c voltages for T3 and T5.
T3 E -40.1v
B -40.6v
C -40.6v
T5 E 0.6v
B 39.0v
C 31.4v
I'll get some pics up when I can, I'm out of town for a couple days. Had time to snag some voltages before i left.
Again, voltages that are impossible for e,b,c locations.
Is it another mistake, or is it possible you have some transistors in backwards?
Well shoot. I was assuming the same pinouts as T1 and T2. Here it is corrected.
T3 E -40.6v
B -40.6v
C -40.1v
T5 E 0.6v
B 39.0v
C 31.4v
T3 pins 1,2,3=C,B,E
T5 pins 1,2,3=E,B,C
Quote from: markorock37 on May 02, 2024, 07:49:32 PMT3 pins 1,2,3=C,B,E
T5 pins 1,2,3=E,B,C
As far as I know, there is no such thing as CBE pinout for these. But, apparently there are 2 versions of each, and could be either EBC or ECB.
Can you post a link to the exact ones that you bought?
https://www.mouser.com/ProductDetail/Central-Semiconductor/BC182-PBFREE?qs=u16ybLDytRZNVcCOxCyJgQ%3D%3D (https://www.mouser.com/ProductDetail/Central-Semiconductor/BC182-PBFREE?qs=u16ybLDytRZNVcCOxCyJgQ%3D%3D)
https://www.mouser.com/ProductDetail/Central-Semiconductor/BC212B-PBFREE?qs=u16ybLDytRammG2LPoFOEA%3D%3D (https://www.mouser.com/ProductDetail/Central-Semiconductor/BC212B-PBFREE?qs=u16ybLDytRammG2LPoFOEA%3D%3D)
Actually looks like both have CBE pinouts
So T3
c -40.1v
b -40.6v
e -40.6v
T5
c 31.4v
b 39.0v
e 0.6v
Is it possible the new ones dont have the same pinout as the originals?
Quote from: markorock37 on May 07, 2024, 12:59:57 AMIs it possible the new ones dont have the same pinout as the originals?
Yes it is possible. Measure resistance from D4 cathode to T5. One of the T5 pins should read zero ohms to D4 cathode. Which pin is it, pin 1,2, or 3?
Which T5 pin reads short to R42?